ARF-induced downregulation of Mip130/LIN-9 protein levels mediates a positive feedback that leads to increased expression of p16Ink4a and p19Arf.
The ARF-MDM2-p53 pathway constitutes one of the most important mechanisms of surveillance against oncogenic transformation, and its inactivation occurs in a large proportion of cancers. Here, we show that ARF regulates Mip130/LIN-9 by inducing its translocation to the nucleolus and decreasing the expression of the Mip130/LIN-9 protein through a post-transcriptional mechanism. The knockdown of Mip130/LIN-9 in p53(-/-) and Arf(-/-) mouse embryonic fibroblasts (MEFs) mimics some effects of ARF, such as the downregulation of B-Myb, impaired induction of G2/M genes, and a decrease in cell proliferation. Importantly, although the knockdown of Mip130/LIN-9 reduced the proliferation of p53 or Arf-null MEFs, only p53(-/-) MEFs showed a senescence-like state and an increase in the expression of Arf and p16. Interestingly, the increase in p16 and ARF is indirect because the Mip130/LIN-9 knockdown decreased the transcription of negative regulators of the Ink4a/Arf locus, such as BUBR1 and CDC6. Chromatin immunoprecipitation assays also reveal that Mip130/LIN-9 occupies the promoters of the BubR1 and cdc6 genes, suggesting that Mip130/LIN-9 is necessary for the expression of these genes. Altogether, these results indicate that there is a feedback mechanism between ARF and Mip130/LIN-9 in which either the increase of ARF or the decrease in Mip130/LIN-9 causes a further increase in the expression of Arf and p16.
Song
J
J
Department of Pharmacology, University of Illinois, Chicago, IL, USA.
Sandoval
R
R
Pilkinton
M A
MA
Tian
X
X
Raychaudhuri
P
P
Colamonici
O R
OR
D000375:Aging / Q000235:genetics; D000818:Animals; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects*; D005347:Fibroblasts / Q000502:physiology; D016158:Genes, p53 / Q000502:physiology; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D041681:NIH 3T3 Cells; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; C512498:LIN-9 protein, mouse; D025521:Tumor Suppressor Proteins