title: The atr protein kinase controls UV-dependent upregulation of p16INK4A through inhibition of Skp2-related polyubiquitination/degradation.
abstract: The tumor suppressor p16(INK4A), a phosphoprotein that exists in human cells under both phosphorylated and nonphosphorylated forms, plays crucial roles during the cellular response to UV light. However, it is still unclear how this protein is activated in response to this carcinogenic agent. We have shown here that UVC upregulates p16(INK4A) and the phosphorylated form of the protein at the 4 serine sites; Ser-7, Ser-8, Ser-140, and Ser-152. This accumulation of p16(INK4A) occurred through increasing the stability of both forms of the protein. Importantly, phospho-p16(INK4A) showed much higher stability, and UV treatment strongly increased its level in absence of de novo protein synthesis. Furthermore, we have shown that the UV-dependent upregulation of both forms of p16(INK4A) is under the control of the protein kinase Atr, which suppresses their UVC-dependent proteasomal degradation. Interestingly, although this degradation is ubiquitin-related for p16(INK4A) through the Skp2 ubiquitin ligase protein, it is ubiquitin-independent for the phosphorylated form. In addition, we present clear evidence that Skp2 is upregulated in ATR-deficient cells, leading to the downregulation of the p27(Kip1) protein in response to UVC light. Moreover, we have shown a preferential association of endogeneous phospho-p16(INK4A) with Cdk4. This association increased following UV-treatment mainly for p16(INK4A) phosphorylated at Ser-140 and Ser-152. Besides, we have shown that Atr regulates UV-related p16/Cdk4-dependent and -independent phosphorylation of pRB and G1 cell cycle delay. Together, these results indicate that p16(INK4A) and p27(Kip1) are key targets in the Atr-dependent signaling pathway in response to UV damage.
authors.affiliation: King Faisal Specialist Hospital and Research Center, Department of Biological and Medical Research, Riyadh, KSA.
authors.forename: Huda H
authors.initials: HH
authors.lastname: Al-Khalaf
authors.forename: Siti-Faujiah
authors.initials: SF
authors.lastname: Hendrayani
authors.forename: Abdelilah
authors.initials: A
authors.lastname: Aboussekhra
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D051358:Cyclin-Dependent Kinase 4 / Q000235:genetics / Q000378:metabolism*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000235:genetics; D014466:Ultraviolet Rays / Q000009:adverse effects; D015854:Up-Regulation / Q000235:genetics
chemical_list: D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D016160:Retinoblastoma Protein; D044786:S-Phase Kinase-Associated Proteins; D016159:Tumor Suppressor Protein p53; D050760:Cyclin-Dependent Kinase Inhibitor p27; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D051358:Cyclin-Dependent Kinase 4