p21 Cooperates with DDB2 Protein in Suppression of Ultraviolet Ray-induced Skin Malignancies

Abstract

Background:The p53-induced genes DDB2 and p21 play antagonistic roles in DNA repair and apoptosis. Results: In UV-induced skin carcinoma, DDB2 and p21 cooperate to prevent carcinoma by inducing premature senescence. Conclusion: Pro-senescence and anti-proliferative pathways are critical protection mechanism against skin malignancies. Significance: Although studies on skin cancer focus on DNA repair mechanisms, this study provides new insights.Exposure to ultraviolet rays (UV) in sunlight is the main cause of skin cancer. Here, we show that the p53-induced genes DDB2 and p21 are down-regulated in skin cancer, and in the mouse model they functionally cooperate to prevent UV-induced skin cancer. Our previous studies demonstrated an antagonistic role of DDB2 and p21 in nucleotide excision repair and apoptosis. Surprisingly, we find that the loss of p21 restores nucleotide excision repair and apoptosis in Ddb2 ؊/؊ mice, but it does not protect from UV-mediated skin carcinogenesis. In contrast, Ddb2 ؊/؊ p21 ؊/؊ mice are significantly more susceptible to UVinduced skin cancer than the Ddb2 ؊/؊ or the p21 ؊/؊ mice. We provide evidence that p21 deletion in the Ddb2 ؊/؊ background causes a strong increase in cell proliferation. The increased proliferation in the Ddb2 ؊/؊ p21 ؊/؊ background is related to a severe deficiency in UV-induced premature senescence. Also, the oncogenic pro-proliferation transcription factor FOXM1 is overexpressed in the p21 ؊/؊ background. Our results show that the anti-proliferative and the pro-senescence pathways of DDB2 and p21 are critical protection mechanisms against skin malignancies.The UV rays in sunlight cause DNA damage by generating cyclobutane pyrimidine dimers and 6-(1,2)-dihydro-2-oxo-4-pyrimidinyl-5-methyl-2,4-(1H,3H)-pyrimidinedione between two adjacent pyrimidines. Both DNA damages lead to distortion of DNA, predisposing cells to accumulate mutations. As a protective mechanism against UV-induced DNA damage, cells utilize nucleotide excision repair (NER) 6 pathway or they undergo apoptosis. Damaged DNA-binding protein 2 (DDB2), a subunit of the damaged DNA-binding protein DDB, encoded by the XP-E gene, plays important roles in both NER and apoptosis following exposure to UV irradiation (1-3). Ddb2 Ϫ/Ϫ mice develop UV-induced skin cancers with much higher incidence in comparison with wild type (WT) mice (4, 5). Enhanced expression of Ddb2 in mice also reduces UV-induced carcinogenesis by delaying the onset of tumor development and also by reducing the number of tumors per mouse, providing further evidence of the role of DDB2 in the inhibition of UV-induced skin tumorigenesis (6).We demonstrated that high accumulation of p21 following exposure to low doses of UV light is the cause for the NER deficiency in the fibroblasts derived from the Ddb2-deficient embryos. DDB2 regulates the level of p21 through multiple mechanisms. DDB2 targets p53 S18P for proteolysis upon low dose of UV irradiation, ensuring lower expression of its downstream transcriptional target p21 (7). DDB2 also targe...

DDB2 association with PCNA is required for its degradation after UV-induced DNA damage

“…The cells were lysed in hypotonic buffer containing 10 mM Tris-HCl (pH 7.4), 2.5 mM MgCl 2 , 1 mM PMSF, 0.5% Nonidet NP-40, 0.2 mM Na 3 VO 4 , and a mixture of protease and phosphatase inhibitor cocktails (Sigma). After 10 min on ice, the cells were pelleted by low-speed centrifugation (200 g, 1 min), and the detergent-soluble fraction was recovered.…”

Tumor regression by phenethyl isothiocyanate involves DDB2

“…4 Deletion of p21 in the DDB2 -/background restored NER activities in mouse embryonic fibroblasts (MEFs) as well as in mouse primary keratinocytes. 8 DDB2 is also an important mediator of apoptosis and senescence. 9,10 MEFs or human cells lacking DDB2 expression are deficient in apoptosis following DNA damage.…”

“…The DDB2 -/-p21 -/mice, on the other hand, exhibit efficient apoptosis. 8 High level of p21 has been implicated in senescence. 12 Despite highlevel p21 accumulation, DDB2 -/-MEFs were found to be deficient in replicative senescence.…”

FOXM1 is a critical driver of lung fibroblast activation and fibrogenesis

“…However, the fact that PGE 2 inhibition of FOXM1 persisted to a substantial degree in the presence of Myr-AKT as well as FOXO3A knockdown suggests an additional FOXO3A-independent mechanism by which PGE 2 interferes with FOXM1 binding to target gene-promoter elements. One possible mechanism that merits future exploration is induction of P21, originally described as a cyclin-dependent kinase inhibitor, but now also recognized as interfering with FOXM1 binding (52), which has been reported to be induced by forskolin (53). PGE 2 inhibition of fibroblast expression/activation of FOXM1 thus represents yet an additional mechanism for the antifibrotic actions of this prostanoid.…”