The role of the tumor suppressors p53 and p16 genes in the cellular response to Ultraviolet light. SUMMARY Proliferating cells respond to DNA damage by concomitantly arresting cellular growth at checkpointsa nd activating DNA repair processesC. ell cycle arrestsa re mediated,i n part, by the inhibition of cyclin-dependent kinases (CDKs), whose function is required for cell cycle progression. p53, p21WAF' and p16`NK4aa re the products of tumor suppressor genes that play important roles during the cellular response to genotoxic stresses. p53 and p16 coding genes have been found mutated or transcriptionally silenced in different cancer types both sporadic and familial. Indeed, p16 has been found to be linked to familial melanoma, whose etiology is related to sun-light induced DNA damage. It is hence important to ascertain whether p53 and p16 are involved in the cellular response to UV damage. In this report I present evidence that p53 is not involved in UV-induced cellular growth arrest in late G1 phase. This has been demonstrated in HeLa cells synchronized at the G1/S border by aphidicolin, followed by UV exposure. Interestingly, the length of this p53-independent G1 arrest has been shown to be UV dose-dependent. Similar results were also obtained with other p53-deficient cell lines, including the human promyelocytic leukemia HL-60 and mouse p53 knock-out cells. As expected, all of these cell lines were defective in v-ray-induced cell growth arrest at late G1Using different assays I also show here that p16-compromised U20S osteosarcoma cells are deficient in the removal of UV damage, as compared to their isogenic derivatives EH1 and EH2 counterparts that express p16. This deficiency is associated with a high level of UV-induced apoptosis, which is significantly reduced in the p16-expressing EH I, EH2 and p16+/+ mouse embryonic fibroblast (MEF) cells, indicating that p16 protects cells from undergoing apoptosis in response to UV light. Importantly, this reduction in UV-mediated apoptosis was associated with down-regulation of the pro-apoptotic Bax protein, with no effect on Bcl-2 expression, suggesting that this anti-apoptotic role of p16 is mediated via the intrinsic p53-dependent mitochondrial pathway. On the other hand, p16 sensitized cells to cisplatin-mediated apoptosis through Bcl-2 decline. Furthermore, I show that p16 is involved in UV-related G1 checkpoint and controls the expression and UV-dependent activation of another CDK inhibitor, p21wAFI. Importantly, this relationship between p16 and p21 exists also in MEFs, suggesting that it is not cell type- or species-dependent. These results indicate that, in addition to its role in cell cycle control and senescence, p16 also plays an important role in the cellular response to UV damage, possibly by inhibiting apoptosis and facilitating cell cycle arrest and photolesion removal. The data presented here provide further insights into the role of p53 and p16, as tumor suppressors, in carcinogenesis and have potential implications for future therapy strategies

No description available.

Thesis (M.S. in biochemistry)--Washington State University, December 2009. / Title from PDF title page (viewed on Jan. 20, 2010). "School of Molecular Biosciences." Includes bibliographical references.

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 137-159).

Thesis (MS)--University of Montana, 2007. / Contents viewed on March 26, 2010. Title from author supplied metadata. Includes bibliographical references.

No description available.

Ionising radiation (IR) induces a wide spectrum of lesions in DNA, including double- and single-strand breaks, abasic (AP) sites and a variety of base lesions. IR-induced damage to DNA can range from simple, isolated lesions to clustered DNA damage in which multiple lesions are formed, usually within a single helical turn of the DNA. Individual lesions within a cluster are recognised by repair enzymes of the base excision repair (BER) pathway, however, clustered DNA damage may be recognised as a bulky lesion and be processed by nucleotide excision repair (NER). Additionally, the presence of other closely spaced lesions may affect the rate and fidelity of DNA repair and, in doing so, may contribute to the harmful effects of ionising radiation. The aim of this study is to gain further understanding of the repairability of clustered DNA damage and the effects of multiple lesions on cellular repair systems. 7, 8-dihydro-8-oxoguanine (8-oxoG), thymine glycol (Tg), AP sites and single-strand breaks (SSB), some of the most frequently formed IR-induced DNA lesions, were employed in synthetic oligonucleotides to model various types of clustered lesions and their repairability was studied using purified base excision repair enzymes and cell extracts. It was revealed that BER is the major repair system involved in the processing of clustered DNA lesions, and that some clustered lesions are repaired with decreased efficiency. Both the composition of lesions in a cluster and the positioning of the various lesions determine their repairability by base excision repair enzymes.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 114-136). Also available in print.

Thesis (M.Sc.)--York University, 2005. Graduate Programme in Biology. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11935

Undergraduate honors paper--Mount Holyoke College, 2007. Program in Biochemistry. / Includes bibliographical references (leaves 107-108).