van Oosten Marijke, Stout Gerdine J, Backendorf Claude, Rebel Heggert, de Wind Niels, Darroudi Firouz, van Kranen Henk J, de Gruijl Frank R, Mullenders Leon Hf
Department of Toxicogenetics, Leiden University Medical Center, Wassenaarseweg 72, 2333 AL Leiden, The Netherlands.
DNA Repair (Amst). 2005 Jan 2;4(1):81-9. doi: 10.1016/j.dnarep.2004.08.008.
Nucleotide excision repair (NER), cell cycle regulation and apoptosis are major defence mechanisms against the carcinogenic effects of UVB radiation. NER eliminates UVB-induced DNA photolesions via two subpathways: global genome repair (GGR) and transcription-coupled repair (TCR). In a previous study, we found UVB-induced accumulation of tetraploid (4N) keratinocytes in the epidermis of Xpc(-/-) mice (no GGR), but not in Xpa(-/-) (no TCR and no GGR) or in wild-type (WT) mice. We inferred that this arrest in Xpc(-/-) mice is caused by erroneous replication past photolesions, leading to 'compound lesions' known to be recognised by mismatch repair (MMR). MMR-induced futile cycles of breakage and resynthesis at sites of compound lesions may then sustain a cell cycle arrest. The present experiments with Xpc(-/-)Msh2(-/-) mice and derived keratinocytes show that the MMR protein Msh2 indeed plays a role in the generation of the UVB-induced arrested cells: a Msh2-deficiency lowered significantly the percentage of arrested cells in vivo (40-50%) and in vitro (30-40%). Analysis of calyculin A (CA)-induced premature chromosome condensation (PCC) of cultured Xpc(-/-) keratinocytes showed that the delayed arrest occurred in late S phase rather than in G(2)-phase. Taken together, the results indicate that in mouse epidermis and cultured keratinocytes, the MMR protein Msh2 plays a role in the UVB-induced S-phase arrest. This indicates that MMR plays a role in the UVB-induced S-phase arrest. Alternatively, Msh2 may have a more direct signalling function.
核苷酸切除修复（NER）、细胞周期调控和细胞凋亡是抵御紫外线B（UVB）辐射致癌作用的主要防御机制。NER通过两条子途径消除UVB诱导的DNA光损伤：全基因组修复（GGR）和转录偶联修复（TCR）。在先前的一项研究中，我们发现UVB诱导四倍体（4N）角质形成细胞在Xpc（-/-）小鼠（无GGR）的表皮中积累，但在Xpa（-/-）小鼠（无TCR和无GGR）或野生型（WT）小鼠中未发现这种情况。我们推断，Xpc（-/-）小鼠中的这种停滞是由光损伤部位的错误复制导致的，从而产生了已知可被错配修复（MMR）识别的“复合损伤”。MMR在复合损伤部位诱导的断裂和重新合成的无效循环可能会维持细胞周期停滞。目前对Xpc（-/-）Msh2（-/-）小鼠及其衍生的角质形成细胞进行的实验表明，MMR蛋白Msh2确实在UVB诱导的停滞细胞的产生中发挥作用：Msh2缺陷显著降低了体内（40-50%）和体外（30-40%）停滞细胞的百分比。对培养的Xpc（-/-）角质形成细胞进行的毛喉素A（CA）诱导的早熟染色体凝聚（PCC）分析表明，延迟停滞发生在S期后期而非G2期。综上所述，结果表明在小鼠表皮和培养的角质形成细胞中，MMR蛋白Msh2在UVB诱导的S期停滞中发挥作用。这表明MMR在UVB诱导的S期停滞中发挥作用。或者，Msh2可能具有更直接的信号功能。
