The tumor-suppressor gene FHIT is involved in the regulation of apoptosis and in cell cycle control

Alteration of the FHIT (fragile histidine triad) gene occurs as an early an d frequent event in lung carcinogenesis, FHIT gene transfer into lung cance r cell line H460 lacking Fhit protein expression resulted in reversion of t umorigenicity. To gain insight into the biological function of FHIT, we com pared the H460 cell line with its Fhit transfectants (H460/FHIT). A signifi cant inhibition of cell growth was observed in H460/FHIT cells. The analysi s of apoptosis by in situ terminal deoxynucleotidyltransferase-mediated dUT P nick end labeling revealed a high rate of apoptosis induced DNA strand br eaks in stable clones, In situ results mere confirmed by FACScan analysis t hat showed an apoptotic rate of 44-47% compared with a 15% level in the con trol H460 cells, Analysis of cell cycle phase distribution indicated a sign ificant G(0)/G(1) arrest and the presence of a sub-G(1) peak in the stable clones. No significant changes in Bcl2, BclX, and Bax protein expression le vel were observed in the transfected clones as compared with the control H4 60 cells whereas a 2-fold increase in Bak protein levels was noticed. An in creased level of p21(waf) protein paralleled by an up-regulation of p21(waf ) transcripts also was found in Fhit-expressing clones compared with the H4 60 cell line. No differences in p53 levels were observed in the same cells, suggesting a p53-independent effect, These data suggest that the observed growth-inhibitory effect in FHIT-reexpressing cells could be related to apo ptosis and cell cycle arrest and link the tumor-suppressor activity of FHIT to its proapoptotic function.