Deficient protein kinase a in systemic lupus erythematosus - A disorder of T lymphocyte signal transduction

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 (RIbeta) steady state mRNA by competitive polymerase chain reaction. This is associated with a 30% decrease in RIalpha protein and a 65% reduction in RIbeta protein. Indeed, T cells from similar to25% of SLE subjects have no detectable RIbeta protein. Transient transfection of T cells not expressing RIbeta protein with autologous SLE RIbeta cDNA bypassed the block in translation, reconstituting PKA activity and augmenting IL-2 production. Of importance was the initial identification of novel RIalpha 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 RIIbeta(2)C(2) holoenzyme, aberrant RIIbeta translocation to the nucleus from the cytosol, and retention of RIIbeta in the nucleus. In conclusion, distinct mechanisms account for deficient PKA-I and PKA-II isozyme activities in SLE T cells.