Intrinsic cooperation between p16INK4a and p21Waf1/Cip1 in the onset of cellular senescence and tumor suppression in vivo.
Although the p16(INK4a) and p21Waf1/Cip1 cyclin-dependent kinase (CDK) inhibitors are known to play key roles in cellular senescence in vitro, their roles in senescence remain rather poorly understood in vivo. This situation is partly due to the possibility of compensatory effect(s) between p16INK4a and p21Waf1/Cip1 or to the upregulation of functionally related CDK inhibitors. To directly address the cooperative roles of p16INK4a and p21Waf1/Cip1 in senescence in vivo, we generated a mouse line simply lacking both p16INK4a and p21Waf1/Cip1 genes [double-knockout (DKO)]. Mouse embryonic fibroblasts (MEF) derived from DKO mice displayed no evidence of cellular senescence when cultured serially in vitro. Moreover, DKO MEFs readily escaped Ras-induced senescence and overrode contact inhibition in culture. This was not the case in MEFs lacking either p16INK4a or p21Waf1/Cip1, indicating that p16(INK4a) and p21Waf1/Cip1 play cooperative roles in cellular senescence and contact inhibition in vitro. Notably, we found the DKO mice to be extremely susceptible to 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate-induced skin carcinogenesis that involves oncogenic mutation of the H-ras gene. Mechanistic investigations suggested that the high incidence of cancer in DKO mice likely reflected a cooperative effect of increased benign skin tumor formation caused by p21Waf1/Cip1 loss, with increased malignant conversion of benign skin tumors caused by p16(INK4a) loss. Our findings establish an intrinsic cooperation between p16INK4a and p21Waf1/Cip1 in the onset of cellular senescence and tumor suppression in vivo.
Divison of Cancer Biology, The Cancer Institute of Japanese Foundation for Cancer Research (JFCR), Tokyo, Japan.
Shinji
S
Takeuchi
Akiko
A
Takahashi
Noriko
N
Motoi
Shin
S
Yoshimoto
Tomoko
T
Tajima
Kimi
K
Yamakoshi
Atsushi
A
Hirao
Shigeru
S
Yanagi
Kiyoko
K
Fukami
Yuichi
Y
Ishikawa
Saburo
S
Sone
Eiji
E
Hara
Naoko
N
Ohtani
D015127:9,10-Dimethyl-1,2-benzanthracene / Q000633:toxicity; D000818:Animals; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002478:Cells, Cultured; D016922:Cellular Senescence; D050762:Cyclin-Dependent Kinase Inhibitor p15 / Q000235:genetics / Q000378:metabolism; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006657:Histones / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012878:Skin Neoplasms / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
D015127:9,10-Dimethyl-1,2-benzanthracene; D050762:Cyclin-Dependent Kinase Inhibitor p15; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D006657:Histones; D050814:Octamer Transcription Factor-3; D013755:Tetradecanoylphorbol Acetate; D018631:ras Proteins; C494174:Pou5f1 protein, mouse; C475961:gamma-H2AX protein, mouse