Cortactin modulates RhoA activation and expression of Cip/Kip cyclin-dependent kinase inhibitors to promote cell cycle progression in 11q13-amplified head and neck squamous cell carcinoma cells.
The cortactin oncoprotein is frequently overexpressed in head and neck squamous cell carcinoma (HNSCC), often due to amplification of the encoding gene (CTTN). While cortactin overexpression enhances invasive potential, recent research indicates that it also promotes cell proliferation, but how cortactin regulates the cell cycle machinery is unclear. In this article we report that stable short hairpin RNA-mediated cortactin knockdown in the 11q13-amplified cell line FaDu led to increased expression of the Cip/Kip cyclin-dependent kinase inhibitors (CDKIs) p21(WAF1/Cip1), p27(Kip1), and p57(Kip2) and inhibition of S-phase entry. These effects were associated with increased binding of p21(WAF1/Cip1) and p27(Kip1) to cyclin D1- and E1-containing complexes and decreased retinoblastoma protein phosphorylation. Cortactin regulated expression of p21(WAF1/Cip1) and p27(Kip1) at the transcriptional and posttranscriptional levels, respectively. The direct roles of p21(WAF1/Cip1), p27(Kip1), and p57(Kip2) downstream of cortactin were confirmed by the transient knockdown of each CDKI by specific small interfering RNAs, which led to partial rescue of cell cycle progression. Interestingly, FaDu cells with reduced cortactin levels also exhibited a significant diminution in RhoA expression and activity, together with decreased expression of Skp2, a critical component of the SCF ubiquitin ligase that targets p27(Kip1) and p57(Kip2) for degradation. Transient knockdown of RhoA in FaDu cells decreased expression of Skp2, enhanced the level of Cip/Kip CDKIs, and attenuated S-phase entry. These findings identify a novel mechanism for regulation of proliferation in 11q13-amplified HNSCC cells, in which overexpressed cortactin acts via RhoA to decrease expression of Cip/Kip CDKIs, and highlight Skp2 as a downstream effector for RhoA in this process.
Croucher
David R
DR
Cancer Research Program, Garvan Institute of Medical Research, Sydney, NSW, Australia.
Rickwood
Danny
D
Tactacan
Carole M
CM
Musgrove
Elizabeth A
EA
Daly
Roger J
RJ
D001483:Base Sequence; D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology*; D002453:Cell Cycle / Q000235:genetics* / Q000502:physiology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics; D051356:Cortactin / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000502:physiology*; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000235:genetics* / Q000502:physiology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000502:physiology; D050760:Cyclin-Dependent Kinase Inhibitor p27; D050761:Cyclin-Dependent Kinase Inhibitor p57 / Q000235:genetics / Q000502:physiology; D017931:DNA Primers / Q000235:genetics; D005784:Gene Amplification; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D006258:Head and Neck Neoplasms / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology; D034741:RNA, Small Interfering / Q000235:genetics; D020742:rhoA GTP-Binding Protein / Q000235:genetics* / Q000502:physiology*
C493956:CDKN1A protein, human; C436291:CDKN1B protein, human; C493964:CDKN1C protein, human; C495868:CTTN protein, human; D051356:Cortactin; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050761:Cyclin-Dependent Kinase Inhibitor p57; D017931:DNA Primers; D047908:Intracellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; C066737:RHOA protein, human; D050760:Cyclin-Dependent Kinase Inhibitor p27; D020742:rhoA GTP-Binding Protein
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