Medema R H, Herrera R E, Lam F, Weinberg R A
Whitehead Institute for Biomedical Research, Nine Cambridge Center, MA 02142, USA.
Proc Natl Acad Sci U S A. 1995 Jul 3;92(14):6289-93. doi: 10.1073/pnas.92.14.6289.
p16ink4 has been implicated as a tumor suppressor that is lost from a variety of human tumors and human cell lines. p16ink4 specifically binds and inhibits the cyclin-dependent kinases 4 and 6. In vitro, these kinases can phosphorylate the product of the retinoblastoma tumor suppressor gene. Thus, p16ink4 could exert its function as tumor suppressor through inhibition of phosphorylation and functional inactivation of the retinoblastoma protein. Here we show that overexpression of p16ink4 in certain cell types will lead to an arrest in the G1 phase of the cell cycle. In addition, we show that p16ink4 can only suppress the growth of human cells that contain functional pRB. Moreover, we have compared the effect of p16ink4 expression on embryo fibroblasts from wild-type and RB homozygous mutant mice. Wild-type embryo fibroblasts are inhibited by p16ink4, whereas the RB nullizygous fibroblasts are not. These data not only show that the presence of pRB is crucial for growth suppression by p16ink4 but also indicate that the pRB is the critical target acted upon by cyclin D-dependent kinases in the G1 phase of the cell cycle.
p16ink4被认为是一种肿瘤抑制因子，在多种人类肿瘤和人类细胞系中缺失。p16ink4特异性结合并抑制细胞周期蛋白依赖性激酶4和6。在体外，这些激酶可磷酸化视网膜母细胞瘤肿瘤抑制基因的产物。因此，p16ink4可能通过抑制视网膜母细胞瘤蛋白的磷酸化和功能失活来发挥其肿瘤抑制功能。在此我们表明，在某些细胞类型中过表达p16ink4会导致细胞周期在G1期停滞。此外，我们表明p16ink4只能抑制含有功能性pRB的人类细胞的生长。而且，我们比较了p16ink4表达对野生型和RB纯合突变小鼠胚胎成纤维细胞的影响。野生型胚胎成纤维细胞受到p16ink4的抑制，而RB纯合缺失的成纤维细胞则不受影响。这些数据不仅表明pRB的存在对p16ink4的生长抑制作用至关重要，还表明pRB是细胞周期G1期细胞周期蛋白D依赖性激酶作用的关键靶点。
