V-SIS INDUCES EGR-1 EXPRESSION BY A PATHWAY MEDIATED BY C-HA-RAS

The early growth response gene, Egr-1, is up-regulated transiently by mitogens and many other stimuli in all cells tested. Using NIH3T3 cell s conditionally expressing v-sis from a metallothionein promoter, we s how that the addition of Zn2+ stimulates the production of PDGF-B (v-s is) and elicits the expression of Egr-1 in a dose-dependent and time-r egulated manner. The signal is likely independent of protein kinase C, but depends on tyrosine kinase and other kinase activities and is med iated by c-Ha-Ras since the presence of dominant-negative mutants of R as and Raf abrogates the induction of Egr-1 expression by Zn2+. Transi ently activated Ras expression in NIH3T3 cells also stimulates the tra nsient expression of Egr-1, but cells that constitutively express Ras do not have elevated levels of Egr-1. Transient assays also demonstrat ed that Zn2+ or activated Ras expression stimulate the activity of a 9 50 bp Egr-1 promoter-reporter gene construct and this is abrogated in the presence of mutant Ras and Rai. The accumulated data show that Egr -1 gene expression is regulated by multiple mechanisms, as would be ne eded for putative roles in cell proliferation, in suppression of trans formation and in differentiation. (C) 1994 Wiley-Liss, Inc.