Regulation of replicative and stress-induced senescence by RSK4, which is down-regulated in human tumors.
OBJECTIVE
The control of senescence and its biochemical pathways is a crucial factor for understanding cell transformation. In a large RNA interference screen, the RSK4 gene was found to be related to p53-dependent arrest. The purpose of the present study was to investigate the potential role of RSK4 as a tumor suppressor gene.


METHODS
RSK4 expression was determined by quantitative real-time PCR and immunoblot in 30 colon and 20 renal carcinomas, and in 7 colon adenomas. Two HCT116 colon carcinoma cell lines (p53 wt and p53 null), IMR90 human fibroblasts, and E1A-expressing IMR90 cells were infected with RSK4 cDNA and/or shRNA. RSK4 expression levels were analyzed in HCT116 p53 wt or p53 null and IMR90 after senescence induction by quantitative real-time PCR and Western blot.


RESULTS
The RSK4 gene was down-regulated in 27 of 30 colon carcinomas (P < 0.001), 16 of 20 renal cell carcinomas (P < 0.01), and 6 of 7 colon adenomas (P < 0.01). In vitro overexpression of RSK4 induced cell arrest and senescence features in normal fibroblasts and malignant colon carcinoma cell lines. Interestingly, in these cell lines RSK4 mRNA levels were increased both in replicative and stress-induced senescence. Moreover, IMR90 partially immortalized by RSK4 shRNA and HCT116 with this short hairpin RNA were more resistant to cisplatin treatment. Finally, cells expressing E1A or Rb short interfering RNA were resistant to RSK4-mediated senescence.


CONCLUSIONS
These results support the concept that RSK4 may be an important tumor suppressor gene by modulating senescence induction and contributing to cell proliferation control in colon carcinogenesis and renal cell carcinomas.
López-Vicente
Laura
L
Department of Pathology, Vall d'Hebron University Hospital, and Department of Biochemistry and Molecular Biology, and Unit of Biological Anthropology, Universitat Autònoma de Barcelona, Barcelona 08035, Spain.
Armengol
Gemma
G
Pons
Berta
B
Coch
Laura
L
Argelaguet
Elisabet
E
Lleonart
Matilde
M
Hernández-Losa
Javier
J
de Torres
Inés
I
Ramon y Cajal
Santiago
S
D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D016922:Cellular Senescence / Q000235:genetics / Q000502:physiology*; D002945:Cisplatin / Q000494:pharmacology; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004261:DNA Replication; D015536:Down-Regulation / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007680:Kidney Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D016160:Retinoblastoma Protein / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics* / Q000378:metabolism; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016877:Oxidants; D034741:RNA, Small Interfering; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D006861:Hydrogen Peroxide; C501305:RPS6KA6 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D002945:Cisplatin