Ribavirin-induced resistance to heat shock, inhibition of the Ras-Raf-1 pathway and arrest in G(1)

Ribavirin [1-(beta-D-ribofuranosyl) 1,2,4-triazole-3-carboxamide (virazole) ], a specific inhibitor of inositide 5'-monophosphate: dehydrogenase (IMPDH ), induces a strong depletion of GTP pools in IGR39 cells. After a 3-day tr eatment, the cell cycle was reversibly arrested in G(0)/G(1), suggesting th e involvement of GTP in the cell cycle process. The reduction of the GTP ce ll content modified the appearance of the microtubule network, as examined using immunofluorescence. However, the dynamics of repolymerisation were no t altered. When arrested in G(0)/G(1), cells displayed a surprising resista nce to a 3-h period of heat shock at 45 degrees C. Considering the lack of coimmunoprecipitation of p21 ras with Raf-1, the reduction of the level of GTP-associated p21ras and the decrease of the activation of the extracellul ar signal-regulated protein kinases (ERK), also known as mitogen-activated protein (MAP) kinase, in ribavirin-treated cells, we suggest a possible rel ationship between the expression of heat-shuck proteins and the change, in GTP-depleted cells, of the regulation of Raf kinase by ras protein. (C) 200 0 Elsevier Science B.V. All rights reserved.