EFFECT OF PHOSPHOTYROSINE PHOSPHATASE OVER-EXPRESSION ON GLUTATHIONE METABOLISM IN NORMAL AND ONCOGENE-TRANSFORMED CELLS

We measured the level of reduced glutathione (GSH) and oxidized glutat hione (GSSG) in normal and oncogene-transformed NIH/3T3 fibroblasts an d 32D hematopoietic cells. NIH/3T3 cells transformed by the activated oncogenes erbB, src, and raf showed increased levels of GSH with conco mitant alterations in the levels of GSH-related enzymes. Transfection and over-expression of a synthetic gene coding for a phosphotyrosine p rotein phosphatase (PTPase), which inhibited the proliferation of norm al and transformed NIH/3T3 cells, was accompanied by a decrease in GSH levels in normal and erbB-transformed fibroblasts, and by an increase in src and raf transformants. Among GSH-related enzymes, only gamma-g lutamylcysteine synthetase was altered in normal and erbB-transformed NIH/3T3 fibroblasts following PTPase transfection. Therefore, tyrosine phosphorylation could be selectively involved in the regulation of GS H metabolism in normal and oncogene-transformed NIH/3T3 fibroblasts, p ossibly by a dual-type effect on receptor/oncoprotein-mediated mitogen ic signal transduction. However, no relationship was observed between the GSH and PTPase effect on cell growth, either after oncogene transf ection or PTPase transfection. Moreover, the changes in GSH metabolism were specifically related to cell lineage. In fact GSH and related en zymes did not change in 32D hematopoietic cells transformed by the sam e activated erbB oncogene and in those - normal or transformed - over- expressing the PTPase: in these cells also, over-expression of the PTP ase gene was not accompanied by growth inhibition.