Deficient type I protein kinase A isozyme activity in systemic lupus erythematosus T lymphocytes.
Systemic lupus erythematosus (SLE) is an autoimmune disorder of indeterminate etiology characterized by a dysfunctional cellular immune response. We have previously identified a metabolic disorder of the adenylate cyclase/cAMP/protein kinase A (AC/cAMP/PKA) pathway characterized by impaired cAMP-inducible, PKA-catalyzed protein phosphorylation in intact T lymphocytes from subjects with severe SLE disease activity. Because this metabolic disorder may contribute to abnormal T cell immune effector functions, we tested the hypothesis that impaired PKA-dependent protein phosphorylation is the result of a PKA isozyme deficiency in SLE T lymphocytes. Compared with healthy and rheumatoid arthritis (RA) controls, subjects with severe SLE activity exhibited reduced PKA-catalyzed phosphorylation of proteins in the T lymphocyte plasma membrane where the type I isozyme of PKA (PKA-I) is predominantly localized. Both silver staining and biosynthetic labeling of membrane-associated proteins with [35S]methionine demonstrated that reduced protein phosphorylation was not due to either an altered distribution of or absence of proteins. Moreover, phosphorylation of SLE membrane-associated proteins with the PKA catalytic (C) subunit showed a similar distribution and extent of phosphorylation compared with membrane proteins from healthy T cells, suggesting that SLE T cell membrane proteins could be phosphorylated. Sequential column chromatography of the type I and type II isozymes of PKA (PKA-I, PKA-II) demonstrated a deficiency of PKA-I isozyme activity. Compared with a ratio of PKA-I to PKA-II activity of 4.2:1 in healthy T cells, the activity ratio in T cells from subjects with severe SLE disease activity was 0.99:1 (P = 0.01, SLE versus healthy controls for PKA-I). The deficient PKA-I activity was associated with a significant increase of free C-subunit activity (P = 0.04, SLE versus healthy controls for C-subunit). T cells from subjects with mild/moderate SLE disease activity also exhibited diminished PKA-I activity, yielding a ratio of PKA-I to PKA-II activity of 2.4:1. By contrast, T cells from RA controls possessed increased PKA-I, PKA-II, and free C-subunit activities compared with healthy controls, resulting in a ratio of PKA-I to PKA-II activity of 3.6:1. We conclude that the reduced PKA-catalyzed protein phosphorylation in the plasma membrane of SLE T cells is the result of deficient PKA-I isozyme activity. This is the first identification of a deficiency of PKA activity in SLE T lymphocytes; the deficiency, resulting in diminished protein phosphorylation, may alter cellular homeostasis, contributing to the cellular immune dysfunctions observed in SLE.
Kammer
G M
GM
Department of Internal Medicine, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, North Carolina 27157.
Khan
I U
IU
Malemud
C J
CJ
D000328:Adult; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000172:deficiency*; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000172:deficiency*; D008180:Lupus Erythematosus, Systemic / Q000201:enzymology*; D008297:Male; D008875:Middle Aged; D010766:Phosphorylation; D013601:T-Lymphocytes / Q000201:enzymology*
D007527:Isoenzymes; D000242:Cyclic AMP; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases