RESUMO
Molecular events were studied in mouse L cells treated with etoposide (VP-16) a drug widely used in cancer therapy. Modulation of the expression of stress response genes belonging to the hsp70 family (hsp70, hsc73, grp78), growth- and cycle-related genes (c-myc, c-fos, c-jun, histone H3) and apoptosis-related genes (p53, TRPM-2, tTG) was monitored at different time points in the cells that remained adherent to the substrate up to 96 hours after exposure to VP-16. The steady state level of mRNA was determined by Northern blot analysis and hybridization with specific probes, and the relative rate of gene transcription was monitored by run on transcription with isolated nuclei. Our results indicate that protracted VP-16 treatment of 1. cells induces, within 24 hours, the arrest of DNA synthesis, repression of growth-related genes and transient induction of the tTG gene. Altogether these molecular events may contribute to the cytotoxic effect of VP-16. However in cells surviving a longer exposure to the drug, the expression of growth-related genes resumes, even if a blockade in DNA replication persists, and expression of the grp78 gene significantly increases. These data suggest that under continuous treatment with VP-16 a fraction of L cells showing increased resistance to the drug may emerge.
