Leukotriene D(4) activates MAPK through a Ras-independent but PKCepsilon-dependent pathway in intestinal epithelial cells.

We have recently shown that leukotriene D-4 (LTD4) increases cell survival in intestinal epithelial cells. Here we report and explore the complementary finding that LTD4 also enhances proliferation in these cells. This proliferative response was approximately half of that induced by epidermal growth factor (EGF) and its required activation of protein kinase C (PKC), Ras and the mitogen-activated protein kinase (MAPK) Erk-1/2. EGF also activated Erk-1/2 in these cells; however the EGF-receptor inhibitor PD153035 did not affect the LTD4-induced activation of Erk-1/2. In addition, LTD4 did not induce phosphorylation of the EGF receptor, nor did pertussis toxin (PTX) block EGF-induced activation of Erk-1/2, thus refuting a possible crosstalk between the receptors. Furthermore, LTD4-induced, but not EGF-Induced, activation of Erk-1/2 was sensitive to PTX, PKC inhibitors and downregulation of PKCepsilon. A definite role for PKCepsilon in LTD4-induced stimulation of Erk-1/2 was documented by the inability of LTD4 to activate Erk-1/2 in cells transfected with either the regulatory domain of PKCepsilon (an isoform specific dominant-negative inhibitor) or a kinase-dead PKCepsilon Although Ras and Raf-1 were both transiently activated by LTD4, only Raf-1 activation was abolished by abrogation of the PKC signal. Furthermore, the LTD4-induced activation of Erk-1/2 was unaffected by transfection with dominant-negative N17 Ras but blocked by transfection with kinase-dead Raf-1. Consequently, LTD4 regulates the proliferative response by a distinct Ras-independent, PKCepsilon-dependent activation of Erk-1/2 and a parallel Ras-dependent signaling pathway.