THIOREDOXIN INCREASES THE PROLIFERATION OF HUMAN B-CELL LINES THROUGHA PROTEIN-KINASE C-DEPENDENT MECHANISM

Thioredoxin (Trx) catalyzes thiol-disulfide oxidoreductions. We and ot hers recently showed that human Trx could function as an autocrine gro wth factor for human lymphoid cells immortalized by the human T-lympho tropic virus type I or the Epstein-Barr virus. Here we report that red uced Trx from Escherichia coli generated by NADPH and thioredoxin redu ctase increases the proliferation of an Epstein-barr virus((+))-B cell line 1G8, which constitutively produces low amounts of human Trx. Thi s proliferative effect involved the activation of protein kinase C thr ough its translocation to the membrane. Staurosporin and calphostin C, two inhibitors of protein kinase C, but not of H8, a protein kinase A inhibitor, were able to block Trx-dependent proliferation. The additi on of Trx to 1G8 cells resulted in the formation of inositol 1,4,5-tri phosphate and sn-1,2-diacylglycerol by a phosphoinositide-specific pho spholipase C, as well as increased free calcium concentration. Diacylg lycerol showed a biphasic increase; the first phase, corresponding to an early peak (30 s) of inositol 1,4,5-triphosphate and a second large r, prolonged phase. The second phase was inhibited by propranolol, a s pecific inhibitor of phosphohydrolase, indicating that it is most like ly derived from phosphatidylcholine hydrolysis by the sequential actio n of phospholipase D and phosphatidic acid phosphohydrolase. Our data suggest that enhanced phosphoinositide-specific phospholipase C activi ty induced by the dithiol form of Trx in 1G8 cells is associated to pr otein kinase C activation, and thus plays a role in the permanent grow th of Epstein-Barr virus-infected B cells.