Regulation of lymphotoxin production by the p21(ras)-raf-MEK-ERK cascade in PHA/PMA-stimulated Jurkat cells

Although the production of lymphotoxin (LT) from activated Th1 lymphocytes has been reported extensively, the intracellular signaling mechanisms that regulate this T cell function remain totally undefined, We have examined wh ether the D21(ras)-raf-1-mitogen-activated protein kinase/extracellular sig nal-regulated protein kinase (ERK) kinase (MEK)-ERK cascade plays a role in regulating the production of LT, because the activity of these signaling m olecules is up-regulated in activated T lymphocytes, Transfection of Jurkat leukemic T cells with a dominant negative mutant of p21(ras) (ras17N or ra s 15A), raf-1 (raf 1-130), or ERK1 (Erk1-K71R) resulted in the suppression of the mitogen/phorbol ester-stimulated production/secretion of LT, This su ppression was accompanied by a parallel inhibition of mitogen-stimulated ER K activation. The selective antagonist of MEK1 activation, PD98059, also at tenuated the mitogen-stimulated or anti-CD3 Ab and phorbol ester-stimulated production of LT from Jurkat cells or peripheral blood T lymphocytes. This study provides, for the first time, direct evidence that the p21(ras)-raf- MEK-ERK cascade plays a vital role in regulating the production of LT.