PP2A:B56ϵ, a Substrate of Caspase-3, Regulates p53-dependent and p53-independent Apoptosis during Development (2010)

Protein phosphatase 2A (PP2A) is one of the most abundantly expressed serine/threonine protein phosphatases. A large body of evidence suggests that PP2A is a tumor suppressor and plays critical roles in regulating apoptosis. PP2A is a heterotrimeric protein complex. Its substrate specificity, localization, and activity are regulated by regulatory subunits of PP2A. A recent study has demonstrated that single nucleotide polymorphism in B56ϵ (PPP2R5E), a B56 family regulatory subunit of PP2A, is associated with human soft tissue sarcoma. This raises the possibility that B56ϵ is involved in tumorigenesis and plays important roles in regulating apoptosis. However, this hypothesis has not been tested experimentally. Our previous studies revealed that B56ϵ regulates a number of developmental signaling pathways during early embryonic patterning. Here we report novel functions of B56ϵ in regulating apoptosis. We provide evidence that B56ϵ has both anti- and pro-apoptotic functions. B56ϵ suppresses p53-independent apoptosis during neural development, but triggers p53-dependent apoptosis. Mechanistically, B56ϵ regulates the p53-dependent apoptotic pathway solely through controlling the stability of p53 protein. In addition to its function in regulating apoptosis, we show that B56ϵ undergoes proteolytic cleavage. The cleavage of B56ϵ is mediated by caspase-3 and occurs on the carboxyl side of an evolutionarily conserved N-terminal “DKXD” motif. These results demonstrate that B56ϵ, a substrate of caspase-3, is an essential regulator of apoptosis. So far, we have identified an alternative translation isoform and a caspase cleavage product of B56ϵ. The significance of post-transcriptional regulation of B56ϵ is discussed. Protein phosphatase 2A (PP2A) is one of the most abundantly expressed serine/threonine protein phosphatases. A large body of evidence suggests that PP2A is a tumor suppressor and plays critical roles in regulating apoptosis. PP2A is a heterotrimeric protein complex. Its substrate specificity, localization, and activity are regulated by regulatory subunits of PP2A. A recent study has demonstrated that single nucleotide polymorphism in B56ϵ (PPP2R5E), a B56 family regulatory subunit of PP2A, is associated with human soft tissue sarcoma. This raises the possibility that B56ϵ is involved in tumorigenesis and plays important roles in regulating apoptosis. However, this hypothesis has not been tested experimentally. Our previous studies revealed that B56ϵ regulates a number of developmental signaling pathways during early embryonic patterning. Here we report novel functions of B56ϵ in regulating apoptosis. We provide evidence that B56ϵ has both anti- and pro-apoptotic functions. B56ϵ suppresses p53-independent apoptosis during neural development, but triggers p53-dependent apoptosis. Mechanistically, B56ϵ regulates the p53-dependent apoptotic pathway solely through controlling the stability of p53 protein. In addition to its function in regulating apoptosis, we show that B56ϵ undergoes proteolytic cleavage. The cleavage of B56ϵ is mediated by caspase-3 and occurs on the carboxyl side of an evolutionarily conserved N-terminal “DKXD” motif. These results demonstrate that B56ϵ, a substrate of caspase-3, is an essential regulator of apoptosis. So far, we have identified an alternative translation isoform and a caspase cleavage product of B56ϵ. The significance of post-transcriptional regulation of B56ϵ is discussed. IntroductionAfter decades of research since the discovery of protein phosphorylation, it is now appreciated that reversible protein phosphorylation is one of the major mechanisms for regulating cellular behavior. Reversible protein phosphorylation is executed by protein kinases and protein phosphatases. The human genome contains more than 500 protein kinase genes (1Manning G. Whyte D.B. Martinez R. Hunter T. Sudarsanam S. Science. 2002; 298: 1912-1934Crossref PubMed Scopus (6126) Google Scholar), but only a small number of protein phosphatases. Interestingly, many protein phosphatases are multimeric enzymes, with a few catalytic subunits being associated with many different regulatory subunits. This gives rise to sufficient numbers of protein phosphatases with different catalytic activity, substrate specificity, or intracellular localization to counteract the activities of protein kinases. Protein phosphatases 2A (PP2A) 2The abbreviations used are: PP2Aprotein phosphatases 2ASNPsingle nucleotide polymorphismEGTearly gastrulation transitionp53 mormorpholino against p53. is one of the most abundantly expressed Ser/Thr protein phosphatases. PP2A holoenzymes consist of a catalytic subunit (PP2Ac), a structural subunit (PP2Aa), and a regulatory subunit (B). Although PP2Ac exhibits fairly poor specificity in vitro, its activity in vivo is tightly regulated by multiple families of PP2A regulatory subunits, including B55/B, B56/B′, and PR72/B″. Investigation into individual regulatory subunits is central to understanding the mechanisms by which PP2A functions in a variety of cellular events (2Cohen P.T. Trends Biochem. Sci. 1997; 22: 245-251Abstract Full Text PDF PubMed Scopus (453) Google Scholar, 3Shi Y. Cell. 2009; 139: 468-484Abstract Full Text Full Text PDF PubMed Scopus (1024) Google Scholar, 4Virshup D.M. Shenolikar S. Mol. Cell. 2009; 33: 537-545Abstract Full Text Full Text PDF PubMed Scopus (485) Google Scholar).PP2A is a tumor suppressor and is targeted by many tumor inducers (5Janssens V. Goris J. Biochem. J. 2001; 353: 417-439Crossref PubMed Scopus (1511) Google Scholar, 6Arroyo J.D. Hahn W.C. Oncogene. 2005; 24: 7746-7755Crossref PubMed Scopus (191) Google Scholar, 7Mumby M. Cell. 2007; 130: 21-24Abstract Full Text Full Text PDF PubMed Scopus (237) Google Scholar, 8Eichhorn P.J. Creyghton M.P. Bernards R. Biochim. Biophys. Acta. 2009; 1795: 1-15Crossref PubMed Scopus (406) Google Scholar), ranging from endogenous or viral proteins, such as SET (9Li M. Makkinje A. Damuni Z. J. Biol. Chem. 1996; 271: 11059-11062Abstract Full Text Full Text PDF PubMed Scopus (401) Google Scholar) or SV40 small t antigen (10Xu Y. Xing Y. Chen Y. Chao Y. Lin Z. Fan E. Yu J.W. Strack S. Jeffrey P.D. Shi Y. Cell. 2006; 127: 1239-1251Abstract Full Text Full Text PDF PubMed Scopus (336) Google Scholar, 11Cho U.S. Xu W. Nature. 2007; 445: 53-57Crossref PubMed Scopus (330) Google Scholar, 12Cho U.S. Morrone S. Sablina A.A. Arroyo J.D. Hahn W.C. Xu W. PLoS Biol. 2007; 5: e202Crossref PubMed Scopus (98) Google Scholar, 13Sablina A.A. Hahn W.C. Cancer Metastasis Rev. 2008; 27: 137-146Crossref PubMed Scopus (76) Google Scholar), to chemical compounds, including okadaic acid (14Suganuma M. Fujiki H. Suguri H. Yoshizawa S. Hirota M. Nakayasu M. Ojika M. Wakamatsu K. Yamada K. Sugimura T. Proc. Natl. Acad. Sci. U.S.A. 1988; 85: 1768-1771Crossref PubMed Scopus (592) Google Scholar). These tumor inducers either inhibit the activity of PP2A or disrupt holoenzyme assembly of PP2A. Consistently, mutations in the structural A subunit have been identified in a range of tumors (15Wang S.S. Esplin E.D. Li J.L. Huang L. Gazdar A. Minna J. Evans G.A. Science. 1998; 282: 284-287Crossref PubMed Scopus (325) Google Scholar, 16Colella S. Ohgaki H. Ruediger R. Yang F. Nakamura M. Fujisawa H. Kleihues P. Walter G. Int. J. Cancer. 2001; 93: 798-804Crossref PubMed Scopus (55) Google Scholar, 17Ruediger R. Pham H.T. Walter G. Oncogene. 2001; 20: 1892-1899Crossref PubMed Scopus (112) Google Scholar, 18Ruediger R. Pham H.T. Walter G. Oncogene. 2001; 20: 10-15Crossref PubMed Scopus (129) Google Scholar, 19Chen W. Arroyo J.D. Timmons J.C. Possemato R. Hahn W.C. Cancer Res. 2005; 65: 8183-8192Crossref PubMed Scopus (124) Google Scholar, 20Sablina A.A. Hahn W.C. Cell. Adh. Migr. 2007; 1: 140-141Crossref PubMed Scopus (32) Google Scholar, 21Sablina A.A. Chen W. Arroyo J.D. Corral L. Hector M. Bulmer S.E. DeCaprio J.A. Hahn W.C. Cell. 2007; 129: 969-982Abstract Full Text Full Text PDF PubMed Scopus (166) Google Scholar). The role of PP2A in tumor suppression appears to be complicated. Accumulating evidence demonstrates that interfering with PP2A may result in errors in chromosome segregation (22Kateneva A.V. Higgins J.M. Dev. Cell. 2009; 17: 303-305Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar, 23Kawashima S.A. Yamagishi Y. Honda T. Ishiguro K. Watanabe Y. Science. 2010; 327: 172-177Crossref PubMed Scopus (344) Google Scholar, 24Rivera T. Losada A. Bioessays. 2006; 28: 775-779Crossref PubMed Scopus (25) Google Scholar, 25Trinkle-Mulcahy L. Lamond A.I. Curr. Opin. Cell. Biol. 2006; 18: 623-631Crossref PubMed Scopus (99) Google Scholar), genomic instability (26Nojima H. Genome Dyn. 2006; 1: 131-148Crossref PubMed Scopus (17) Google Scholar), and insensitivity to apoptotic signals (5Janssens V. Goris J. Biochem. J. 2001; 353: 417-439Crossref PubMed Scopus (1511) Google Scholar, 6Arroyo J.D. Hahn W.C. Oncogene. 2005; 24: 7746-7755Crossref PubMed Scopus (191) Google Scholar, 7Mumby M. Cell. 2007; 130: 21-24Abstract Full Text Full Text PDF PubMed Scopus (237) Google Scholar, 8Eichhorn P.J. Creyghton M.P. Bernards R. Biochim. Biophys. Acta. 2009; 1795: 1-15Crossref PubMed Scopus (406) Google Scholar). At the molecular level, one of the most important pathways regulated by PP2A is the p53-dependent apoptotic pathway. In this pathway, p53 regulates the balance between the pro- and anti-apoptotic BCL family members through G. Nature. 2009; PubMed Scopus Google Scholar, A.V. Biochim. Biophys. Acta. 2009; PubMed Scopus Google Scholar) or Rev. Cancer. 2002; PubMed Scopus Google Scholar, Y. E. Cancer Res. 2001; PubMed Scopus Google Scholar) In the of a variety of p53 protein is and to the of pro-apoptotic BCL family This results in and of PP2A regulates this pathway multiple that PP2A and its S.S. H. M. Arroyo J.D. Hahn W.C. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). PP2A function of and p53 Mol. Cell. Biol. 2008; 28: PubMed Scopus Google Scholar, J. 2007; PubMed Scopus Google Scholar) or through controlling the activity of K. M. Mol. Cell. Biol. 1996; PubMed Scopus Google Scholar, K. Li H. T. Y. S.S. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, H. 2002; PubMed Scopus Google Scholar), the that triggers the of to the regulatory subunit family D.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), which plays critical roles in regulating apoptosis A. A. D.M. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U.S.A. 2002; PubMed Scopus Google Scholar, W. H. Martinez Mol. Cell. 2007; Full Text Full Text PDF PubMed Scopus Google Scholar, T. F. Oncogene. 2009; 28: PubMed Scopus Google Scholar, J.A. J. Biol. Chem. 2008; Full Text Full Text PDF PubMed Scopus Google Scholar, T. M. 2007; PubMed Scopus Google Scholar). Our previous studies demonstrate that B56ϵ regulates a number of including and We to functions of B56ϵ into the and pathways Z. Shi J. A. W. Strack S. Yang J. J. Biol. Chem. 2009; Full Text Full Text PDF PubMed Scopus Google Scholar, W. Yang J. Dev. Biol. 2007; PubMed Scopus Google Scholar, J. J. 130: PubMed Scopus (76) Google Scholar). a recent which human single nucleotide that p53 identified a between B56ϵ and human soft tissue sarcoma. that a in the of B56ϵ, with but of human soft tissue A. P. H. Cancer Res. 2009; PubMed Scopus Google Scholar). Although it the of B56ϵ, it raises the possibility that B56ϵ plays an important role in regulating the p53-dependent apoptotic pathway. Interestingly, it has been that of both B56 family members in apoptosis in a p53-dependent A. A. D.M. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U.S.A. 2002; PubMed Scopus Google Scholar). by we the function of B56ϵ in regulating apoptosis during Our the evidence that B56ϵ is involved in apoptotic We show that B56ϵ has anti- and pro-apoptotic functions during B56ϵ suppresses p53-independent apoptosis, but plays a role in p53 and p53-dependent apoptosis. Interestingly, B56ϵ undergoes cleavage. The cleavage occurs on the carboxyl side of an evolutionarily conserved N-terminal “DKXD” and results in a of B56ϵ. These results demonstrate that B56ϵ, a substrate of caspase-3, is an essential regulator of demonstrate that B56ϵ has both anti- and pro-apoptotic functions. The anti-apoptotic of B56ϵ in the neural by B56ϵ not by of that B56ϵ is for p53-independent apoptosis during neural the by which B56ϵ suppresses apoptosis in the neural that B56ϵ is for of the neural W. Yang J. Dev. Biol. 2007; PubMed Scopus Google Scholar, J. J. 130: PubMed Scopus (76) Google Scholar), we the possibility that the apoptosis by B56ϵ is an of neural patterning. Interestingly, it has been that of SV40 small t which with B56 for the of the (10Xu Y. Xing Y. Chen Y. Chao Y. Lin Z. Fan E. Yu J.W. Strack S. Jeffrey P.D. Shi Y. Cell. 2006; 127: 1239-1251Abstract Full Text Full Text PDF PubMed Scopus (336) Google Scholar, 11Cho U.S. Xu W. Nature. 2007; 445: 53-57Crossref PubMed Scopus (330) Google Scholar, 12Cho U.S. Morrone S. Sablina A.A. Arroyo J.D. Hahn W.C. Xu W. PLoS Biol. 2007; 5: e202Crossref PubMed Scopus (98) Google Scholar), p53-independent apoptosis in J. 2001; PubMed Scopus Google Scholar). is that B56ϵ functions as a regulator of the p53-independent apoptotic In addition to its anti-apoptotic role during neural development, B56ϵ as a pro-apoptotic in the p53-dependent apoptotic pathway. We show that of B56ϵ the of p53 protein. This occurs in the of that B56ϵ regulates p53 protein through a with its role in of B56ϵ caspase-3, as by cleavage of B56ϵ, and triggers apoptosis in both caspase and apoptosis in to B56ϵ be by interfering with p53. This demonstrates that B56ϵ regulates the p53-dependent apoptotic pathway solely through controlling the stability of p53 p53 through phosphorylation of p53 which the between p53 and PP2A and results in of p53 by PP2A. of and p53 in to Mol. Cell. Biol. 2008; 28: PubMed Scopus Google Scholar, J. 2007; PubMed Scopus Google Scholar). In addition to the roles of B56ϵ and B56 family members a role in regulation of p53. The genome contains B56 regulatory subunits. Although of individual B56 genes of both and apoptosis in and and embryonic to the A. A. D.M. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U.S.A. 2002; PubMed Scopus Google Scholar). The of B56 on be by of p53 A. A. D.M. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar), that B56 regulates p53 to of B56 family members the of p53 in we that p53 or a regulator of p53 is a substrate by of this protein by is essential for p53 protein a to the B56 family this p53 individual B56 is However, the of of B56ϵ or is B56 family members are be of to this hypothesis in the is the molecular through which B56ϵ regulates the stability of of has on the of p53 in J. 2007; PubMed Scopus Google Scholar), of B56ϵ p53. is that B56ϵ and p53 through Interestingly, evidence suggests that B56 family members p53 by controlling the between p53 and In this a of p53 S. K. Y. H. Cell. PubMed Scopus (55) Google Scholar, A. A. M. Oncogene. Google Scholar), to and the between and p53 by and K. M. Mol. Cell. Biol. 1996; PubMed Scopus Google Scholar, K. Li H. T. Y. S.S. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, H. 2002; PubMed Scopus Google Scholar). A number of B56 family members have been to with K. M. Mol. Cell. Biol. 1996; PubMed Scopus Google Scholar, T. J.L. H. L. A.A. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). it is to that B56ϵ the stability of p53 through the addition to its role in regulating apoptosis, B56ϵ undergoes proteolytic cleavage. This cleavage occurs on the carboxyl side of a conserved and is mediated by appears that cleavage of B56ϵ has an on the stability of B56ϵ protein. Interestingly, cleavage of endogenous B56ϵ be but occurs of the p53-dependent apoptotic pathway. This it that cleavage of B56ϵ only during apoptosis. of B56ϵ, as a molecular for the of caspase-3 and p53-dependent apoptosis. However, it is important to that we the possibility that cleavage of B56ϵ occurs Although including caspase-3, in most have functions A. Curr. Opin. Biol. 2002; PubMed Scopus Google Scholar, K. Biochem. PubMed Scopus Google Scholar). In addition to function in the apoptotic pathway, caspase-3 is involved in and for P. K. Proc. Natl. Acad. Sci. U.S.A. 2002; PubMed Scopus Google Scholar). of caspase-3 in has been in a number of studies A. S. J. PubMed Scopus Google Scholar, S. S. E. Y. G. W. 2002; PubMed Scopus Google Scholar, V. F. A. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar, R. Cell. Res. 1998; PubMed Scopus Google Scholar, J. K. M. J. 2001; PubMed Scopus Google Scholar). it is that the of in is the of In this cleavage may provide an to the of B56ϵ. is that the of B56ϵ contains multiple conserved Ser/Thr phosphorylation on has been S. M. J. S. Chem. 2009; PubMed Scopus Google Scholar). Although the significance of phosphorylation it is that phosphorylation on N-terminal Ser/Thr has an important on the function of B56ϵ. the N-terminal cleavage results in a of B56ϵ that is regulated by the N-terminal is that cleavage as a to protein results are of studies of and from In E. M. S. P. P.J. F. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar) that an anti-apoptotic protein that the of is a substrate of The of by is for the anti-apoptotic function of The of exhibits a anti-apoptotic activity E. M. S. P. P.J. F. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). In the of caspase cleavage a of which the p53 pathway and apoptosis. an of to caspase cleavage and its anti-apoptotic function E. S. G. S. P. J. P. J. G. F. 2010; 17: PubMed Scopus Google Scholar). appears that is an important regulatory to protein we identified an alternative translation isoform of B56ϵ Z. Shi J. A. W. Strack S. Yang J. J. Biol. Chem. 2009; Full Text Full Text PDF PubMed Scopus Google Scholar). In the we report that B56ϵ undergoes cleavage. into the significance of post-transcriptional regulation of B56ϵ, we the of to a with we to between and between PP2Ac and of B56ϵ the This suggests that is in a PP2A may with the catalytic subunit with a is for the pathway during Z. Shi J. A. W. Strack S. Yang J. J. Biol. Chem. 2009; Full Text Full Text PDF PubMed Scopus Google Scholar). is the by which regulates hypothesis is that functions as a and regulates signaling by of endogenous Interestingly, the N-terminal acid of B56ϵ, it contains for with and PP2Ac (10Xu Y. Xing Y. Chen Y. Chao Y. Lin Z. Fan E. Yu J.W. Strack S. Jeffrey P.D. Shi Y. Cell. 2006; 127: 1239-1251Abstract Full Text Full Text PDF PubMed Scopus (336) Google Scholar, 11Cho U.S. Xu W. Nature. 2007; 445: 53-57Crossref PubMed Scopus (330) Google Scholar). of between and raises the possibility that the of B56ϵ, which not with subunits of PP2A, plays a regulatory role during PP2A holoenzyme the study demonstrates that B56ϵ suppresses p53-independent apoptosis during neural and p53-dependent apoptosis through p53. B56ϵ undergoes to an cleavage study is to molecular mechanisms by which B56ϵ regulates apoptosis. IntroductionAfter decades of research since the discovery of protein phosphorylation, it is now appreciated that reversible protein phosphorylation is one of the major mechanisms for regulating cellular behavior. Reversible protein phosphorylation is executed by protein kinases and protein phosphatases. The human genome contains more than 500 protein kinase genes (1Manning G. Whyte D.B. Martinez R. Hunter T. Sudarsanam S. Science. 2002; 298: 1912-1934Crossref PubMed Scopus (6126) Google Scholar), but only a small number of protein phosphatases. Interestingly, many protein phosphatases are multimeric enzymes, with a few catalytic subunits being associated with many different regulatory subunits. This gives rise to sufficient numbers of protein phosphatases with different catalytic activity, substrate specificity, or intracellular localization to counteract the activities of protein kinases. Protein phosphatases 2A (PP2A) 2The abbreviations used are: PP2Aprotein phosphatases 2ASNPsingle nucleotide polymorphismEGTearly gastrulation transitionp53 mormorpholino against p53. is one of the most abundantly expressed Ser/Thr protein phosphatases. PP2A holoenzymes consist of a catalytic subunit (PP2Ac), a structural subunit (PP2Aa), and a regulatory subunit (B). Although PP2Ac exhibits fairly poor specificity in vitro, its activity in vivo is tightly regulated by multiple families of PP2A regulatory subunits, including B55/B, B56/B′, and PR72/B″. Investigation into individual regulatory subunits is central to understanding the mechanisms by which PP2A functions in a variety of cellular events (2Cohen P.T. Trends Biochem. Sci. 1997; 22: 245-251Abstract Full Text PDF PubMed Scopus (453) Google Scholar, 3Shi Y. Cell. 2009; 139: 468-484Abstract Full Text Full Text PDF PubMed Scopus (1024) Google Scholar, 4Virshup D.M. Shenolikar S. Mol. Cell. 2009; 33: 537-545Abstract Full Text Full Text PDF PubMed Scopus (485) Google Scholar).PP2A is a tumor suppressor and is targeted by many tumor inducers (5Janssens V. Goris J. Biochem. J. 2001; 353: 417-439Crossref PubMed Scopus (1511) Google Scholar, 6Arroyo J.D. Hahn W.C. Oncogene. 2005; 24: 7746-7755Crossref PubMed Scopus (191) Google Scholar, 7Mumby M. Cell. 2007; 130: 21-24Abstract Full Text Full Text PDF PubMed Scopus (237) Google Scholar, 8Eichhorn P.J. Creyghton M.P. Bernards R. Biochim. Biophys. Acta. 2009; 1795: 1-15Crossref PubMed Scopus (406) Google Scholar), ranging from endogenous or viral proteins, such as SET (9Li M. Makkinje A. Damuni Z. J. Biol. Chem. 1996; 271: 11059-11062Abstract Full Text Full Text PDF PubMed Scopus (401) Google Scholar) or SV40 small t antigen (10Xu Y. Xing Y. Chen Y. Chao Y. Lin Z. Fan E. Yu J.W. Strack S. Jeffrey P.D. Shi Y. Cell. 2006; 127: 1239-1251Abstract Full Text Full Text PDF PubMed Scopus (336) Google Scholar, 11Cho U.S. Xu W. Nature. 2007; 445: 53-57Crossref PubMed Scopus (330) Google Scholar, 12Cho U.S. Morrone S. Sablina A.A. Arroyo J.D. Hahn W.C. Xu W. PLoS Biol. 2007; 5: e202Crossref PubMed Scopus (98) Google Scholar, 13Sablina A.A. Hahn W.C. Cancer Metastasis Rev. 2008; 27: 137-146Crossref PubMed Scopus (76) Google Scholar), to chemical compounds, including okadaic acid (14Suganuma M. Fujiki H. Suguri H. Yoshizawa S. Hirota M. Nakayasu M. Ojika M. Wakamatsu K. Yamada K. Sugimura T. Proc. Natl. Acad. Sci. U.S.A. 1988; 85: 1768-1771Crossref PubMed Scopus (592) Google Scholar). These tumor inducers either inhibit the activity of PP2A or disrupt holoenzyme assembly of PP2A. Consistently, mutations in the structural A subunit have been identified in a range of tumors (15Wang S.S. Esplin E.D. Li J.L. Huang L. Gazdar A. Minna J. Evans G.A. Science. 1998; 282: 284-287Crossref PubMed Scopus (325) Google Scholar, 16Colella S. Ohgaki H. Ruediger R. Yang F. Nakamura M. Fujisawa H. Kleihues P. Walter G. Int. J. Cancer. 2001; 93: 798-804Crossref PubMed Scopus (55) Google Scholar, 17Ruediger R. Pham H.T. Walter G. Oncogene. 2001; 20: 1892-1899Crossref PubMed Scopus (112) Google Scholar, 18Ruediger R. Pham H.T. Walter G. Oncogene. 2001; 20: 10-15Crossref PubMed Scopus (129) Google Scholar, 19Chen W. Arroyo J.D. Timmons J.C. Possemato R. Hahn W.C. Cancer Res. 2005; 65: 8183-8192Crossref PubMed Scopus (124) Google Scholar, 20Sablina A.A. Hahn W.C. Cell. Adh. Migr. 2007; 1: 140-141Crossref PubMed Scopus (32) Google Scholar, 21Sablina A.A. Chen W. Arroyo J.D. Corral L. Hector M. Bulmer S.E. DeCaprio J.A. Hahn W.C. Cell. 2007; 129: 969-982Abstract Full Text Full Text PDF PubMed Scopus (166) Google Scholar). The role of PP2A in tumor suppression appears to be complicated. Accumulating evidence demonstrates that interfering with PP2A may result in errors in chromosome segregation (22Kateneva A.V. Higgins J.M. Dev. Cell. 2009; 17: 303-305Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar, 23Kawashima S.A. Yamagishi Y. Honda T. Ishiguro K. Watanabe Y. Science. 2010; 327: 172-177Crossref PubMed Scopus (344) Google Scholar, 24Rivera T. Losada A. Bioessays. 2006; 28: 775-779Crossref PubMed Scopus (25) Google Scholar, 25Trinkle-Mulcahy L. Lamond A.I. Curr. Opin. Cell. Biol. 2006; 18: 623-631Crossref PubMed Scopus (99) Google Scholar), genomic instability (26Nojima H. Genome Dyn. 2006; 1: 131-148Crossref PubMed Scopus (17) Google Scholar), and insensitivity to apoptotic signals (5Janssens V. Goris J. Biochem. J. 2001; 353: 417-439Crossref PubMed Scopus (1511) Google Scholar, 6Arroyo J.D. Hahn W.C. Oncogene. 2005; 24: 7746-7755Crossref PubMed Scopus (191) Google Scholar, 7Mumby M. Cell. 2007; 130: 21-24Abstract Full Text Full Text PDF PubMed Scopus (237) Google Scholar, 8Eichhorn P.J. Creyghton M.P. Bernards R. Biochim. Biophys. Acta. 2009; 1795: 1-15Crossref PubMed Scopus (406) Google Scholar). At the molecular level, one of the most important pathways regulated by PP2A is the p53-dependent apoptotic pathway. In this pathway, p53 regulates the balance between the pro- and anti-apoptotic BCL family members through G. Nature. 2009; PubMed Scopus Google Scholar, A.V. Biochim. Biophys. Acta. 2009; PubMed Scopus Google Scholar) or Rev. Cancer. 2002; PubMed Scopus Google Scholar, Y. E. Cancer Res. 2001; PubMed Scopus Google Scholar) In the of a variety of p53 protein is and to the of pro-apoptotic BCL family This results in and of PP2A regulates this pathway multiple that PP2A and its S.S. H. M. Arroyo J.D. Hahn W.C. J. Biol. Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Scholar). PP2A function of and p53 Mol. Cell. Biol. 2008; 28: PubMed Scopus Google Scholar, J. 2007; PubMed Scopus Google Scholar) or through controlling the activity of K. M. Mol. Cell. Biol. 1996; PubMed Scopus Google Scholar, K. Li H. T. Y. S.S. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, H. 2002; PubMed Scopus Google Scholar), the that triggers the of to the regulatory subunit family D.M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), which plays critical roles in regulating apoptosis A. A. D.M. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U.S.A. 2002; PubMed Scopus Google Scholar, W. H. Martinez Mol. Cell. 2007; Full Text Full Text PDF PubMed Scopus Google Scholar, T. F. Oncogene. 2009; 28: PubMed Scopus Google Scholar, J.A. J. Biol. Chem. 2008; Full Text Full Text PDF PubMed Scopus Google Scholar, T. M. 2007; PubMed Scopus Google Scholar). Our previous studies demonstrate that B56ϵ regulates a number of including and We to functions of B56ϵ into the and pathways Z. Shi J. A. W. Strack S. Yang J. J. Biol. Chem. 2009; Full Text Full Text PDF PubMed Scopus Google Scholar, W. Yang J. Dev. Biol. 2007; PubMed Scopus Google Scholar, J. J. 130: PubMed Scopus (76) Google Scholar). a recent which human single nucleotide that p53 identified a between B56ϵ and human soft tissue sarcoma. that a in the of B56ϵ, with but of human soft tissue A. P. H. Cancer Res. 2009; PubMed Scopus Google Scholar). Although it the of B56ϵ, it raises the possibility that B56ϵ plays an important role in regulating the p53-dependent apoptotic pathway. Interestingly, it has been that of both B56 family members in apoptosis in a p53-dependent A. A. D.M. Mol. Cell. Biol. 2002; 22: PubMed Scopus Google Scholar, Proc. Natl. Acad. Sci. U.S.A. 2002; PubMed Scopus Google Scholar). by we the function of B56ϵ in regulating apoptosis during Our the evidence that B56ϵ is involved in apoptotic We show that B56ϵ has anti- and pro-apoptotic functions during B56ϵ suppresses p53-independent apoptosis, but plays a role in p53 and p53-dependent apoptosis. Interestingly, B56ϵ undergoes cleavage. The cleavage occurs on the carboxyl side of an evolutionarily conserved N-terminal “DKXD” and results in a of B56ϵ. These results demonstrate that B56ϵ, a substrate of caspase-3, is an essential regulator of apoptosis.