Abstract:
The object of the invention is based on inhibiting specific phosphorylation on Thr248 and/or Thr250 residues of human transcription factor E2F4 to inhibit somatic endoreduplication processes in postmitotic cells which may be associated with various pathological conditions. The invention covers all currently known methods for the specific inhibition of protein phosphorylation (including the expression of mutant forms of E2F4 without Thr residues phosphorylated by p38MAPK) or methods developed in the future that may be applied to Thr-248 and/or Thr-250 residues of human transcription factor E2F4.

Description:
FIELD OF THE ART 
       [0001]    The present invention belongs to the pharmaceutical sector, relating specifically to molecular target identification for developing therapeutic tools. 
       PRIOR STATE OF THE ART 
       [0002]    The association existing between cell cycle reactivation in postmitotic cells with subsequent de novo DNA synthesis and various pathological processes affecting both neurons (neurodegeneration, ischemia, etc.) and myocytes (hypertrophic cardiomyopathy, vascular pathologies associated with hypertension and aging) is known. In many cases, cell cycle reactivation does not involve cell division but rather is part of an endoreduplication mechanism (Ullah et al., 2009) which translates into the generation of somatic polyploidy (polyploidy that only affects certain cell types and is not passed on from generation to generation). Perhaps one example of a pathology associated with somatic polyploidy is Alzheimer&#39;s disease (AD). It is known that in this disease neurons reactivate the cell cycle before degenerating (Yang et al., 2003), increasing nuclear DNA content (Arendt et al., 2010). These neurons are likely to experience morphological and functional modifications compromising their survival (Frade and López-Sánchez, 2010). In fact, it has been described that hyperploid neurons are those that predominantly degenerate in the brain of patients with AD (Arendt et al., 2010). Cardiac muscle tissue also contains a percentage of polyploid myocytes, the proportion of which may be altered in pathological situations (Yabe and Abe, 1980; Vliegen et al., 1995). Vascular smooth muscle can also suffer impairments associated with polyploidy (McCrann et al. 2008). For these reasons, knowledge of the molecular base involved in endoreduplication will facilitate the design of therapeutic tools that prevent pathologies associated with somatic polyploidization. Therapeutic tools aiming to prevent somatic endoreduplication associated with human pathologies have not been developed until now, most likely because it is a very recent field of research in which new concepts are starting to emerge. 
         [0003]    US20080139517A1 proposes administering one or more agents capable of inhibiting neuronal cell cycle progression either in an early cell cycle phase or by reducing mitogenic stimulation in age associated memory impairment (AAMI), mild cognitive impairment (MCI), AD, cerebrovascular dementia and other retrogenic neurodegenerative conditions. However, said patent document assumes that the degenerative process is associated with conventional cell cycle progression and not endoreduplication. Furthermore, this patent document does not extend the spectrum to other nervous system and heart diseases in which polyploidy-generating cell cycle reactivation has been or may be described. 
         [0004]    It is indicated in Morillo et al., 2010, that the endoreduplication process in neurons leading to neuronal tetraploidy occurs naturally during embryonic development, giving rise to specific neuron populations that acquire a larger size, longer dendrites, and differential innervation regions in their target tissue (Morillo et al., 2010). Endoreduplication in these neurons is known to occur as a response to nerve growth factor NGF-mediated activation of neurotrophins receptor p75 (p75 NTR ). These neurons duplicate their DNA and remain in a G2-like state due to the effect of neurotrophin BDNF which acts through its TrkB receptor preventing G2/M transition. Therefore, neuronal tetraploidization is known to take place during NGF-mediated nervous system development through p75 NTR , the activity of transcription factor E2F1, to re-enter the cell cycle. Those tetraploid neurons that do not receive sufficient BDNF signal try to perform mitosis followed by apoptotic death. In the brain of Alzheimer&#39;s patients, the presence of p75 NTR  and NGF in the affected regions is known. This suggests that the hyperploidy observed in the affected neurons may be caused by the same mechanism that generates tetraploid neurons during nervous system development. Reduced TrkB levels observed in advanced stages of the disease could facilitate neuronal death (see the development of this model in Frade and López-Sánchez, 2010). 
         [0005]    Deschênes et al. 2004 makes reference to the mechanisms for regulating human intestinal epithelial cell proliferation and differentiation and indicates possible phosphorylation of transcription factor E2F4 by p38 MAPK . However, this document concludes that there is currently a need to investigate which residues of transcription factor E2F4 would be phosphorylated by p38 MAPK  as part of the mechanisms for regulating human intestinal epithelial cell proliferation and differentiation. 
         [0006]    None of these documents identifies candidate molecules as therapeutic targets for inhibiting pathological polyploidization. Therefore, there is currently a need to prevent endoreduplication causing pathological polyploidization in postmitotic cells as a therapeutic method by means of identifying new therapeutic targets. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0007]    The present invention relates to an inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , for use in the prevention and/or treatment of a pathology associated with somatic polyploidy. Likewise, the present invention relates to a method for the prevention and/or treatment of a pathology associated with somatic polyploidy, characterized in that it comprises administering to the patient a therapeutically effective amount of an inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 of SEQ ID No: 1. 
         [0008]    Finally, the present invention relates to the use of an inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , as a therapeutic target in the prevention and/or treatment of a pathology associated with somatic polyploidy. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0009]    In a preferred embodiment of the present invention, the inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , for use in the prevention and/or treatment of a pathology associated with somatic polyploidy, is characterized in that it is a mutant form of transcription factor E2F4, the amino acid sequence of which is identified as SEQ ID No: 1 (human). Said mutant form of transcription factor E2F4 with SEQ ID No: 1 is preferably substituted in Thr248 and/or Thr250 residues with an amino acid that cannot be phosphorylated by p38 MAPK , other than glutamate or aspartate. Said amino acid that cannot be phosphorylated is more preferably alanine. 
         [0010]    In another preferred embodiment of the present invention, the inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , for use in the prevention and/or treatment of a pathology associated with somatic polyploidy, is characterized in that it is an E2F4 fragment comprised in SEQ ID No: 1, with identical capacity for interfering with phosphorylation of endogenous E2F4 by p38 MAPK . 
         [0011]    In another preferred embodiment of the present invention, the inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , for use in the prevention and/or treatment of a pathology associated with somatic polyploidy, is characterized in that it is a form of E2F4 from another species with mutations on conserved Thr residues. Said form of E2F4 from another species is preferably selected from SEQ ID No 2 (chicken) and SEQ ID No 3 (mouse) (see  FIG. 1 ). 
         [0012]    In another preferred embodiment of the present invention, the inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , for use in the prevention and/or treatment of a pathology associated with somatic polyploidy, is characterized in that it is a synthetic molecule mimicking the mutant form of transcription factor E2F4 of SEQ ID No: 1, substituted with alanine on Thr248 and/or Thr250 residues. 
         [0013]    On the other hand, the present invention relates to the inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , for use in the prevention and/or treatment of a pathology associated with somatic polyploidy, characterized in that said somatic polyploidy occurs as a result of endoreduplication in postmitotic cells. Said postmitotic cells are preferably neurons and/or myocytes. 
         [0014]    Additionally, the present invention relates to the inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 by p38 MAPK , for use in the prevention and/or treatment of a pathology associated with somatic polyploidy, characterized in that said pathology associated with somatic polyploidy is selected from the following group: neurodegenerative disease, ischemia, hypertrophic cardiomyopathy, vascular pathology associated with hypertension and aging. Said pathology associated with somatic polyploidy is preferably a neurodegenerative disease. Said neurodegenerative disease is even more preferably Alzheimer&#39;s disease. 
         [0015]    In another preferred embodiment of the present invention, the method for the prevention and/or treatment of a pathology associated with somatic polyploidy, which comprises administering to the patient a therapeutically effective amount of an inhibitory agent for inhibiting phosphorylation on Thr248 and/or Thr250 residues of transcription factor E2F4 of SEQ ID No: 1, is characterized in that said inhibitory agent can be comprised in either a peptide or protein associated with another cell membrane-permeable peptide facilitating the intake thereof into the cell, or else in a vector capable of infecting neurons and/or myocytes, preferably suitable for gene therapy, said vector is more preferably a viral vector, and said viral vector is even more preferably a lentivirus. 
         [0016]    Our laboratory has unveiled the mechanism used by NGF/p75 NTR  to induce cell cycle reactivation in neurons of chicken during embryonic development, an effect which generates endoreduplication and neuronal tetraploidy (Morillo et al., 2010). Said mechanism is based on the activation of Ser/Thr kinase p38 MAPK  in the nucleus of affected cells ( FIG. 2 ), and subsequent phosphorylation on threonine residues of transcription factor E2F4 ( FIG. 3 ). Any other signaling pathway that activates p38 MAPK  in postmitotic cells could result in hyperploidization using transcription factor E2F4. In chicken, there are only two residues that can be phosphorylated by p38 MAPK , i.e., threonine residues Thr261 and Thr263 ( FIG. 1 ). The use of NetPhosK 1.0 software predicts that these threonine residues are immersed in a domain conserved with human and mouse E2F4 proteins ( FIG. 1 ). In the case of human E2F4 protein, the threonine residue that can be phosphorylated by p38 MAPK , as predicted by NetPhosk 1.0 software, is threonine residue Thr248 (the consensus site for phosphorylation by p38 MAPK  must have a consecutive Pro residue, a TP sequence, located after said threonine). Human Thr 250 residue has also been considered to be protected even though it lacks a consecutive Pro residue. The reason is its degree of conservation with mouse Thr251 threonine residue and chicken Thr263 threonine residue, both with a consecutive Pro residue and predicted by NetPhosK 1.0 software as threonine residues that can be phosphorylated by p38 MAPK . 
         [0017]    Phosphorylation of Thr261/Thr263 residues of E2F4 is crucial for cell cycle reactivation induced by NGF through p75 NTR  in chick embryo retinal cells in neuronal differentiation process ( FIG. 4 ). Such cell cycle reactivation leads to neuronal tetraploidy (Morillo et al., 2010). We have observed that the use of a constitutively active form of chicken E2F4, in which Thr261 and Thr263 residues have been substituted with Glu (a positively charged amino acid mimicking the phosphorylated state of Thr) is capable of mimicking the effect of NGF on retinal neurons ( FIG. 4A ,  FIG. 4B ). It has also been demonstrated that the use of a negative dominant form of chicken E2F4 (Thr261Ala/Thr263Ala) preventing phosphorylation thereof by p38 MAPK  is capable of inhibiting the effect of NGF on the cell cycle in neurogenic retinal cultures ( FIG. 4C ,  FIG. 4D ). Therefore, it is foreseeable that the expression of this mutant form Thr261Ala/Thr263Ala (or the human form Thr248Ala/Thr250Ala) in affected neurons or myocytes associated with the pathologies described above could inhibit the endoreduplication process and the subsequent hyperploidization, which could prevent, or at least slow down, disease progression. The present invention relates to the use of said mutant forms of E2F4 for preventing hyperploidization and the associated pathological effects in various diseases affecting postmitotic cells (neurons and muscle cells). 
         [0018]    Therefore, the present invention demonstrates that phosphorylation on conserved homologous Thr residues of Thr248 and Thr250 of human E2F4 is crucial for inducing endoreduplication in retinal neurons. 
         [0019]    This invention also protects any method for specifically inhibiting phosphorylation on Thr248 and/or Thr250 residues of human transcription factor E2F4 (hereinafter phosphoE2F4). The inhibition of said phosphorylation would hinder the capacity of E2F4 for inducing DNA synthesis in postmitotic cells, which has clear therapeutic benefits. 
         [0020]    The present invention also relates to any method for inhibiting p38 MAPK /phosphoE2F4 signaling, preferably by means of a mutant form of E2F4 in which the Thr 248 residue and/or Thr250 residue has/have been substituted with an Ala residue, as performed in our laboratory with chicken E2F4. 
         [0021]    Alternatively, the present invention also relates to any other method for inhibiting p38 MAPK /phosphoE2F4 signaling, such as for example:
   substitution of Thr248 and/or Thr250 residues with other amino acids that cannot be phosphorylated,   use of an E2F4 fragment with identical capacity for interfering with the phosphorylation of endogenous E2F4,   use of forms of E2F4 from other species with mutations on conserved Thr residues,   use of synthetic molecules mimicking the mutated form of E2F4, etc.   
 
         [0026]    The present invention also protects any means for specifically transferring the aforementioned mutated forms of E2F4 into affected cells, such as for example, by means of suitable vectors, peptides that can go through the cell membrane, etc. 
         [0027]    The invention involves the following phases: 
         [0028]    1) Generating the blocking molecule which blocks phosphorylation of human transcription factor E2F4 in target cells 
         [0029]    The molecule chosen for blocking phosphorylation on Thr248 and/or Thr250 residues of human E2F4 (whether it is the gene coding sequence for human E2F4 or E2F4 from another species, the peptide sequence of human E2F4 or E2F4 from another species, the partial gene coding sequence for human E2F4 or E2F4 from another species, the partial peptide sequence of human E2F4 or E2F4 from another species, or another molecule mimicking the region or regions of interaction between E2F4 and p38 MAPK  capable of blocking phosphorylation on Thr248 and/or Thr250 residues of human E2F4) will be generated by chemical synthesis or by means of cloning the cDNA sequence in a plasmid that can generate suitable vectors for gene therapy. 
         [0030]    In this last case, the coding sequence must first be amplified with a heat stable enzyme with proof-reading capacity from cDNA derived from mRNA previously obtained from a cell line or from a tissue of human origin. To clone the sequence, primers in which restriction sites that are compatible with the polylinker of the vector chosen for cloning have been included, are used. Said vector is chosen based on the method used in Example 4 for introducing the chosen sequence into the target cells. Once the sequence is cloned, a standard site-directed mutagenesis process leading to the specific modification of ACT codon encoding Thr248 and/or Thr250 residues is performed in order to transform said codon into a codon specific for any amino acid except Glu or Asp. The plasmid thus generated is co-transfected into a suitable cell line capable of packaging the vector of interest. 
         [0031]    2) Expressing the blocking molecule which blocks phosphorylation of human transcription factor E2F4 in target cells 
         [0032]    In those cells in which the p38 MAPK -E2F4 signaling pathway is active, p3 MAPK  is expected to be inhibited upon binding to the excess molecules mimicking the mutated form of E2F4, capable of interacting with p38 MAPK  but incapable of being phosphorylated. The endoreduplication process in said cells is therefore blocked. The blocking molecules can be expressed by the same target cells if they are transferred in the form of DNA (using suitable vectors such as lentivirus, for example). Alternatively, the blocking molecules can be transferred by means of peptides capable of going through the cell membrane with greater or less target cell-type specificity. 
         [0033]    Throughout the description and claims, the word “comprises” and variants thereof do not intend to exclude other technical features, additives, components or steps. For persons skilled in the art, other objects, advantages and features of the invention will be inferred in part from the description and in part from the practice of the invention. The following drawings and examples are provided by way of illustration and they are not meant to limit the present invention. 
       DESCRIPTION OF THE DRAWINGS 
       [0034]      FIG. 1  shows the structure, functional domains and sequence conservation of transcription factor E2F4. The drawing illustrates the comparison between amino acid sequences of human transcription factor E2F4 ( H. sapiens ), mouse ( M. musculus ) transcription factor E2F4, chicken ( G. gallus ) transcription factor E2F4, frog  Xenopus laevis  ( X. laevis ) transcription factor E2F4 and zebrafish ( D. rerio ) transcription factor E2F4. The different known functional domains including the DNA-binding (DB) region, the dimerization (DIM) domain, the marked box (MB) and the transactivation (TA) domain are also indicated. The region including Thr248 and Thr250 residues of the human sequence conserved in other species (indicated by small rectangles) is also indicated: Thr249 and Thr251 residues in the mouse sequence, Thr261 and Thr263 residues in the chicken sequence, Thr228 residue in frog and Thr217 residue in zebrafish. This region is referred to as the regulator domain (RD). Amino acids completely conserved in the regulator domain are indicated with a dot. 
         [0035]      FIG. 2  shows that nuclear p38 MAPK  activation in response to NGF is necessary for cycle reactivation in chick embryo retinal cell neurogenic cultures in E6. These cells respond to NGF by inducing cell cycle reactivation that leads to somatic tetraploidy (endoreduplication) (Morillo et al., 2010). A. Western blot with anti-active p38 MAPK  (P-p38 MAPK ) and anti-p38 MAPK  in nuclear extracts of the mentioned neurogenic cultures treated for the indicated time with 100 ng/ml NGF. The normalized ratios between P-p38 MAPK  and p38 MAPK  levels are indicated at the bottom. B. Immunohistochemical staining with anti-active p38 MAPK  antibodies (P-p38 MAPK ) in the mentioned neurogenic cultures treated with 100 ng/ml NGF for 20 minutes. The nuclei were labeled with bisbenzimide (Bisb.). Note the signal increase in the nucleus of cells treated with NGF. C. Luciferase assay in extracts of chick embryo retinal cell neurogenic cultures E6 transfected with a plasmid expressing luciferase under the control of cMyc gene promoter, known for its response to E2F during G1/S transition, and another plasmid with the constitutive expression of β-galactosidase. The luciferase/β-galactosidase ratio values are depicted as “luciferase activity”. Treatment with 100 ng/ml NGF entails cMyc promoter activation, indicating cell cycle reactivation. This effect is blocked with selective p38 MAPK  inhibitor SB203580 (used at 5 μM). D. Incorporation of BrdU to indicate entry into S phase in chick embryo retinal cell neurogenic cultures E6. Treatment with 100 ng/ml NGF entails an increase in the proportion of cells in S phase, an effect which is blocked by selective p38 MAPK  inhibitor SB203580 (used at 5 μM), but not by selective JNK inhibitor, SP600125 (used at 7 μM). *p&lt;0.05; ***p&lt;0.005 (Student&#39;s t-test) 
         [0036]      FIG. 3  shows NGF-promoted phosphorylation on threonine residues of E2F4 in chick embryo retinal cell neurogenic cultures in E6. The top part shows a Western blot carried out with anti-phosphoThr antibodies (αp-Thr) in extracts immunoprecipitated with anti-E2F4 antibodies originating from the indicated cultures treated with different combinations of 100 ng/ml NGF and selective inhibitor SB203580 (used at 5 μM). The bottom part shows a Western blot carried out with anti-E2F4 antibodies in the same extracts without immunoprecipitation (INPUT). The presence of NGF can be seen to involve an increase in phosphorylation on threonine residues, while the presence of p38 MAPK  inhibitor inhibits such phosphorylation. 
         [0037]      FIG. 4  shows that phosphorylation on Thr261 /Thr263 residues of E2F4 is capable of inducing cycle reactivation in chick embryo retinal cell neurogenic cultures in E6. A. Luciferase activity analyzed as described in  FIG. 2C . The expression of the constitutively active form of E2F4 (E2F4-CA) characterized by Thr261Glu/Thr263Glu substitutions induces cMyc promoter activity, an effect that can be observed even in the presence of selective p38 MAPK  inhibitor SB203580 (used at 5 μM). B. The incorporation of BrdU increases significantly in cells transfected with the constitutively active form of E2F4 (E2F4-CA), an effect that can be observed even in the presence of selective p38 MAPK  inhibitor SB203580 (used at 5 μM). Based on the results shown in panels A and B, it is deduced that p38 MAPK  acts exclusively through Thr261/Thr263 residues. C. Luciferase activity analyzed as described in  FIG. 2C . The expression of the negative dominant form of E2F4 (E2F4-ND) characterized by Thr261Ala/Thr263Ala substitutions prevents the effect of 100 ng/ml NGF on cMyc promoter activity. D. The expression of the negative dominant form of E2F4 (E2F4-ND) prevents the effect of 100 ng/ml NGF on the incorporation of BrdU in retinal neurogenic cultures. 
         [0038]      FIG. 5  shows the diagram of the method for cloning E2F4 coding sequence into a plasmid that allows generating a suitable vector for gene therapy (lentivirus, etc.), for example. The mRNA obtained from human tissue or cells is converted into cDNA using reverse transcriptase. The human E2F4 coding sequence is depicted as a gray rectangle in which the position of the codon encoding Thr 248 residue is indicated. This codon is flanked by two specific restriction sites (C and D). Two primers are designed based on the sequence of the ends of the coding region with a specific restriction site at the 5′ ends (A and B) thereof. These targets also appear in the polylinker of the expression vector and are used for cloning the E2F4 coding sequence into said vector. P: promoter responsible for the transcription of E2F4 protein. pol: polyadenylation sequence used for introducing a poly(A) tail in the mRNA generated by the vector. 
         [0039]      FIG. 6  shows the diagram of the E2F4 coding sequence mutagenesis process. A pair of external primers flanking restriction sites C and D (external arrows) and another overlapping pair of internal primers including in the sequence thereof the mutagenized codon of Thr248 (internal arrows) are designed. Two PCR amplification reactions are performed with DNA polymerase Pfu and the reaction products are denatured together. After renaturing the DNA, the situation indicated in the diagram is obtained, among other possibilities. Elongation with DNA polymerase Pfu creates DNA double helices with the sequences of the external primers at the ends thereof. These sequences are exponentially amplified with said primers resulting in DNA fragments with Thr248 residue mutagenized to Ala, flanked by restriction sites C and D. The sequence containing the mutation can be sub-cloned into the expression vector using restriction sites C and D for that purpose. 
       References 
       [0000]    
       
         Arendt T, Brückner M K, Mosch B, Lösche A. (2010) Selective cell death of hyperploids neurons in Alzheimer&#39;s disease.  Am. J. Pathol.  177:15-20. 
         Deschênes et al. 2004 “The Nucleocytoplasmic Shuttling of E2F4 Is Involved in the Regulation of Human Intestinal Epithelial Cell Proliferation and Differentiation”. 
         Frade J M, López-Sánchez N. (2010) A novel hypothesis for Alzheimer disease based on neuronal tetraploidy induced by p75NTR.  Cell Cycle  9:1934-1941. 
         McCrann D J, Nguyen H G, Jones M R, Ravid K. (2008) Vascular smooth muscle cell polyploidy: an adaptive or maladaptive response?  J. Cell Physiol.  215:588-592. 
         Morillo S M, Escoll P, de la Hera A, Frade J M. (2010) Somatic tetraploidy in specific chick retinal ganglion cells induced by nerve growth factor.  Proc. Natl. Acad. Sci. USA  107:109-114. 
         Ullah Z, Lee C Y, Lilly M A, DePamphilis M L. (2003) Developmentally programmed endoreduplication in animals.  Cell Cycle  8:1501-1509. 
         Vliegen H W, Eulderink F, Bruschke A V, van der Laarse A, Cornelisse C J. (1995) Polyploidy of myocyte nuclei in pressure overloaded human hearts: a flow cytometric study in left and right ventricular myocardium.  Am. J. Cardiovasc. Pathol.  5:27-31. 
         Yabe Y, Abe H. (1980) Changes in DNA synthesis in significantly hypertrophied human cardiac muscle.  Adv. Myocardiol.  1:553-563. 
         Yang Y, Mufson E J, Herrup K. (2003) Neuronal cell death is preceded by cell cycle events at all stages of Alzheimer&#39;s disease.  J. Neurosci.  23:2557-2563. 
       
     
       EXAMPLES 
       [0049]    The following specific examples provided in this patent document serve to illustrate the nature of the present invention. These examples are included merely for illustrative purposes and must not be interpreted as limiting the invention herein claimed. The examples described below therefore illustrate the invention without limiting the field of application thereof. 
       Example 1 
     Cloning Human E2F4 Coding Sequence 
       [0050]    Human E2F4 coding sequence (positions 64-1305 of the sequence with NCBI accession number: NM — 001950) (SEQ ID No 4) is cloned into a plasmid that can generate suitable vectors for gene therapy (lentiviral vectors, for example). The coding sequence must be previously amplified with DNA polymerase enzyme Pfu from cDNA derived from mRNA previously obtained from a cell line or from a tissue of human origin. To clone the sequence, primers including EcoRV and PacI restriction sites (underlined in the sequences indicated at the end of this paragraph) that are compatible with the polylinker of lentiviral expression vector are used (see a simple diagram of said vector in  FIG. 5 , the EcoRV site would correspond to A and the PacI site would correspond to B in said diagram). Examples of these oligonucleotides are as follows: 
         [0000]    
       
         
               
               
             
           
               
                   
                 SEQ ID No 5: 5′ oligo:  
               
               
                   
                 5′-CAACA GATATC ATGGCGGAGGCCGGGCCACA-3′ 
               
               
                   
                   
               
               
                   
                 SEQ ID No 6: 3′ oligo:  
               
               
                   
                 5′-CCA TTAATTAA GGGTCCCAGCCACACAGGGC-3′ 
               
             
          
         
       
     
         [0051]    The first one corresponds to nucleotides in positions 64-83 and the second one is complementary to nucleotides in positions 1319-1338 of the human E2F4 sequence. 
         [0052]    The amplicon thus obtained is cloned into pGEM-Teasy vector (Promega) which does not have EcoRV or PacI restriction sites, in which site-directed mutagenesis described in Section 2 will be performed. 
       Example 2 
     Mutating Thr248 Residue (Thr250 residue can be mutated by means of a similar method once the Thr248Ala mutation is generated) 
       [0053]    Once the human E2F4 sequence is cloned into the pGEM-Teasy vector, oligonucleotides are designed in the region comprised between positions 731-754 of human E2F4 coding sequence, corresponding to SEQ ID No 4. 
         [0054]    These oligonucleotides include ACT codon encoding Thr248 residue (in positions 742-744 of human E2F4 coding sequence) that is mutated as Ala specific codon (GCT sequence). Examples of these oligonucleotides are: 
         [0000]    
       
         
               
             
           
               
                 SEQ ID No 7: 5′ mutated oligo:  
               
               
                 5′-TCAGCTC G CTCCCACTGCTG-3′ (positions 735-754). 
               
               
                   
               
               
                 SEQ ID No 8: 3′ mutated oligo:  
               
               
                 5′-CAGTGGGAG C GAGCTGAGGA-3′ (positions 732-751). 
               
             
          
         
       
     
         [0055]    These oligonucleotides (containing the underlined mutation) will be used as primers of two independent reactions indicated in  FIG. 6 . Another pair of primers flanking enzyme BspEI restriction sites (indicated as C and D in  FIG. 6 ) is designed for these reactions. The cDNA sequence encoding human E2F4 include two BspEI sites in positions 374-379 and 979-984 with TCCGGA sequence. Examples of these primers are: 
         [0000]    
       
         
               
             
           
               
                 SEQ ID No 9: 5′ non-mutated oligo:  
               
               
                 5′-AAGGTGTGGGTGCAGCAGAG-3′ (position 352-371) 
               
               
                   
               
               
                 SEQ ID No 10: 3′ non-mutated oligo:  
               
               
                 5′-GGTCTGCCTTGATGGGCTCA-3′ (position 1005-1025) 
               
             
          
         
       
     
         [0056]    Two PCR amplification reactions are subsequently performed with DNA polymerase Pfu as indicated in the diagram of  FIG. 6  ( 5 ′ non-mutated oligo with 3′mutated oligo and 5′mutated oligo with 3′ non-mutated oligo), and the reaction products are denatured together. After renaturing the DNA, the situation indicated in the diagram of  FIG. 6  is obtained, among other possibilities. Elongation of these hybrids with DNA polymerase Pfu creates DNA double helices that can be amplified with external primers (5′ non-mutated oligo and 3′ non-mutated oligo; see  FIG. 6 ). DNA fragments with Thr248 residue mutagenized to Ala, flanked by restriction sites C and D (see  FIG. 6 ), are therefore obtained. The sequence containing the mutation can then be sub-cloned into pGEM-Teasy plasmid generated in point 1, using restriction sites C and D (BspEI) for that purpose. After sequencing the modified clones, a clone in which the sequence has been incorporated in the suitable orientation is selected. 
       Example 3 
     Generating vectors for therapy that can infect the nervous system 
       [0057]    pGEM-Teasy plasmid with the mutated human E2F4 coding sequence (T248A) is cleaved with EcoRV and PacI enzymes to release said sequence and is sub-cloned into the polylinker of the lentiviral expression vector pSMPUW-Hygro (Cell Biolabs, Inc.) containing the EcoRV and PacI sites. The vector thus generated is co-transfected into a suitable cell line capable of packaging the vector of interest. 
       Example 4 
     Expressing the mutated form of E2F4 in target cells 
       [0058]    In those neurons or myocytes in which the p38 MAPK -E2F4 signaling pathway is active, p38 MAPK  is expected to be inhibited upon binding to an excess of mutated E2F4 molecules, similarly to that observed in neurons treated with NGF in the differentiation process. The endoreduplication process in said cells is thus blocked. Given that phosphorylation on Thr248 residue of E2F4 does not take place in other cell functions with the exception of endoreduplication, its presence in other cells should not have side effects.