title: Growth suppression by p16ink4 requires functional retinoblastoma protein.
abstract: 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.
authors.affiliation: Whitehead Institute for Biomedical Research, Nine Cambridge Center, MA 02142, USA.
authors.forename: R H
authors.initials: RH
authors.lastname: Medema
authors.forename: R E
authors.initials: RE
authors.lastname: Herrera
authors.forename: F
authors.initials: F
authors.lastname: Lam
authors.forename: R A
authors.initials: RA
authors.lastname: Weinberg
mesh_terms: D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000096:biosynthesis / Q000378:metabolism; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis / Q000378:metabolism*; D002455:Cell Division; D002460:Cell Line; D003001:Cloning, Molecular; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16; D018844:Cyclin-Dependent Kinases; D017931:DNA Primers; D015870:Gene Expression; D016147:Genes, Tumor Suppressor; D006801:Humans; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D015183:Restriction Mapping; D016160:Retinoblastoma Protein / Q000378:metabolism*; D014162:Transfection
chemical_list: D000952:Antigens, Polyomavirus Transforming; D002352:Carrier Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D017931:DNA Primers; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D016160:Retinoblastoma Protein; D017346:Protein Serine-Threonine Kinases; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases