Overexpression of G1/S cyclins and PCNA and their relationship to tyrosinephosphorylation and dephosphorylation during tumor promotion by metanil yellow and malachite green

Metanil yellow (MY) and Malachite green (MG) are textile dyes, which, despi te the ban, occur unscrupulously as food colouring agents. Accordingly they constitute a serious public health hazard and are of sufficient environmen tal concern. We have earlier reported that both MY and MG have tumor promot ing effects on the development of hepatic preneoplastic lesions induced by N-nitrosodielhylamine in rats. In order to understand the possible mechanis m(s) by which metanil yellow (MY) and malachite green (MG) promotes liver t umor development, we have studied the tyrosine phosphorylation and protein phosphatases during tumor promotion. We have also investigated the possible overexpression of G1/S cyclins and PCNA during tumor promotion by MY and M G. The present investigation indicates that enhanced tyrosine phosphorylati on is associated with no change in levers of tyrosine protein phosphatases. We have also observed an increase in the expression of PCNA and G1/S cycli ns during tumor promotion. These factors collectively may contribute to the abnormal cell proliferation during tumor promotion by MY and MG. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.