Expression of G1 cell cycle markers and the effect of adenovirus-mediated overexpression of p21Waf-1 in squamous cell carcinoma of the esophagus

To determine the crucial abnormality in the cell cycle regulatory proteins in human squamous cell carcinoma of the esophagus, we examined the cell gro wth ratio (CGR) and basal expression levels of G1 cyclins (cyclin D1, cycli n E), cyclin-dependent kinase (cdk) 2, cdk4, proliferating cell nuclear ant igen (PCNA), and p21Waf-1 using 9 cell lines (KE3, KE4, TE8, TE9, TE10, TE1 1, YES1, YES2, and YES6). Western blotting revealed an inverse linear corre lation between the basal levels of p21Waf-1 expression and CGR. The protein levels of G1 cyclins, cdks, and PCNA did not coordinately reflect the CGR. There was no relationship between p21Waf-1 expression levels and mutation of the p53 gene. Next, when the cells were stimulated with serum 48 h after the starvation, stimulated levels of the above G1 cell cycle markers were variously observed among cell lines irrespective of CGR,Serum stimulation m arkedly induced phosphorylated Rb in TE9 (a high CGR cell line, CGR>2.0), b ut not in KE4 (a low CGR cell line, CGR<1.5). Furthermore, adenovirus-media ted expression of exogenous p21Waf-1 effectively reduced cell growth in KE3 and TE9 (high CGR cell lines), but not in KE4 and TE11 (low CGR cell lines ). p21Waf-1-mediated growth suppression was associated with the induction o f involucrin, a marker of squamous cell differentiation. Our data suggested that the basal level, but not the stimulated level, of p21Waf-1 expression Flay a pivotal role in abnormal growth in human squamous cell carcinoma of the esophagus.