Involvement of Ras and MAP kinase (ERK-1) in cisplatin-induced activation of murine bone marrow-derived macrophages.

Abstract

Cisplatin (cis-diamminedichloroplatinum II), a potent antitumor compound, stimulates immune responses by activating monocytes/macrophages and other cells of the immune system. However, the mechanism by which cisplatin activates these cells is poorly characterised. Our earlier findings indicate that cisplatin treatment stimulates rapid tyrosine phosphorylation in a number of cellular proteins in murine macrophages. This initial tyrosine phosphorylation is an important regulatory mechanism and is followed by activation of several other proteins. In the present study, we report the involvement of other key molecules and the role of tyrosine phosphorylation in their activation in the signaling cascade of cisplatin. We observed the involvement of Ras (a low molecular weight GTP-binding protein) and ERK-1 (a MAP kinase) in this signaling cascade. Cisplatin treatment results in an increase in the expression of both Ras and ERK-1 in a dose-dependent manner, which was dependent upon tyrosine phosphorylation. Genistein a PTK inhibitor inhibited the cisplatin induced expression of Ras and ERK-1. These findings indicate that Ras and ERK-1 are important signaling molecules involved in the tumoricidal activation of macrophages with cisplatin and is dependent on initial tyrosine phosphorylation.