Deficient Protein Kinase A in Systemic Lupus Erythematosus
Systemic lupus erythematosus (SLE) is an idiopathic autoimmune disease characterized by impaired T lymphocyte immune effector functions. We have identified a disorder of signal transduction in SLE T cells involving the cyclic AMP/protein kinase A (cAMP/PKA) pathway. Cyclic AMP-stimulated PKA-catalyzed protein phosphorylation is markedly diminished owing to profound deficiencies of both type I (PKA-I) and type II (PKA-II) isozyme activities. Deficient PKA-I isozyme is characterized by a significant reduction in the amount of type I regulatory beta subunit (RI?) steady state mRNA by competitive polymerase chain reaction. This is associated with a 30% decrease in RI? protein and a 65% reduction in RI? protein. Indeed, T cells from ?25% of SLE subjects have no detectable RI? protein. Transient transfection of T cells not expressing RI? protein with autologous SLE RI? cDNA bypassed the block in translation, reconstituting PKA activity and augmenting IL-2 production. Of importance was the initial identification of novel RI? mRNA mutations characterized by heterogeneous transcript mutations, including deletions, transitions, and transversions. Most mutations are clustered adjacent to GAGAG motifs and CT repeats. By contrast, deficient PKA-II activity is the result of spontaneous dissociation of the cytosolic RII?2C2 holoenzyme, aberrant RII? translocation to the nucleus from the cytosol, and retention of RII? in the nucleus. In conclusion, distinct mechanisms account for deficient PKA-I and PKA-II isozyme activities in SLE T cells.
autoimmunity t lymphocytes protein phosphorylation translation transcription