Activation of RB tumor suppressor protein and growth suppression of small cell lung carcinoma cells by reintroduction of p16(INK4A) gene

The p16(INK4A) tumor suppressor gene is frequently inactivated in non-small cell lung carcinoma (NSCLC) and is less frequently inactivated in small ce ll lung carcinoma (SCLC) by mutation, deletion or DNA methylation. There ar e several reports that the reintroduction of the p16(INK4A) gene into p16(( -)) NSCLC cells results in significant growth suppression. However, there h ave been no reports of reintroduction of the p16(INK4A) gene into SCLC cell s. To assess the biological significance of p16(INK4A) inactivation in the development of SCLC, full-length p16(INK4A) cDNA was introduced into an SCL C cell line, Ms-13, in which the p16(INK4A) protein was not detected. SCLC cells stably transfected with the p16(INK4A) expression vector formed only 2-16% of the number of neomycin-resistant colonies formed by cells transfec ted with a control vector, and no expression of exogenous p16(INK4A) protei n was detected in any of 16 expanded clones. Transient transfection of the p16(INK4A) gene into SCLC cells resulted in exogeneous p16(INK4A) protein e xpression and dephosphorylation of endogenous retinoblastoma (RB) protein. These results suggest that the restoration of the p16(INK4A) function suppr esses the growth of SCLC cells by dephosphorylation of the RE protein. Ther efore, inactivation of p16(INK4A) may play an important role in the enhance ment of growth of p16(INK4A)((-)) RB((+)) SCLC tumors in vivo.