Retinoic acid-mediated G1 arrest is associated with induction of p27(Kip1)and inhibition of cyclin-dependent kinase 3 in human lung squamous carcinoma CH27 cells

Retinoids are promising agents for the prevention and treatment of several human malignancies including lung cancer. In this study, the effect of reti noic acid (RA) on cell growth and the mechanism of growth modulation were e xamined in human lung squamous carcinoma CH27 cells. Here we report that RA mediated the dose-and time dependent growth arrest in G1 phase, accompanie d by the up-regulation of p27(Kip1) and the downregulation of the cyclin-de pendent kinase 3 (Cdk3) and p21(CIP1/Waf1) proteins. Furthermore, RA-induce d growth arrest of CH27 cells was also associated with increased retinoic a cid receptor beta (RAR beta) and reduced c-Myc expression. However, RA had no effect on the levels of cyclins A, D1, D3, E, or H, or on Cdk2, Cdk4, Cd k5, CDk6, Cdk7, p16(Ink4A), p15(Ink4B), p53, or pRb proteins in CH27 cells. Evaluation of the kinase activity of cyclin-Cdk complexes showed that RA i ncreases p27(Kip1) expression in CH27 cells leading to markedly reduced cyc lin A/Cdk2 kinase activity and slightly reduced cyclin E/Cdk2 kinase activi ty, with no effect on cyclin D/Cdk4 and cyclin D/Cdk6 activities. Moreover, coincident with the decrease in kinase activity was a drastic increase in cyclin A-bound p27(Kip1). These results suggest that increases in the level s of p27(Kip1) and its binding to cyclin A, as well as reduction of Cdk3 pr otein expression, are strong candidates for the cell cycle regulator that p revents the entry into the S phase in HA-treated CH27 cells, with prolongat ion of G1 phase and inhibition of DNA synthesis. (C) 2000 Academic Press.