Yang Guang, Curley David, Bosenberg Marcus W, Tsao Hensin
Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts 02114, USA.
Cancer Res. 2007 Jun 15;67(12):5649-57. doi: 10.1158/0008-5472.CAN-06-3806.
Despite an extensive body of evidence linking UV radiation and melanoma tumorigenesis, a clear mechanistic understanding of this process is still lacking. Because heritable mutations in both INK4a and the nucleotide excision repair (NER) pathway predispose individuals to melanoma development, we set out to test the hypothesis that abrogation of NER, by deletion of the xeroderma pigmentosum C (Xpc) gene, will heighten melanoma photocarcinogenesis in an Ink4a-Arf-deficient background. Experimentally, we generated a strain of mice doubly deficient in Xpc and Ink4a-Arf and subjected wild-type, Xpc-/-Ink4a-Arf+/+, Xpc-/-Ink4a-Arf-/-, and Xpc+/+Ink4a-Arf-/- mice to a single neonatal (day P3) dose of UVB without additional chemical promotion. Indeed, there was a significant increase in the development of dermal spindle/epithelioid cell melanomas in Xpc-/-Ink4a-Arf-/- mice when compared with Xpc+/+Ink4a-Arf-/- mice (P = 0.005); wild-type and Xpc-/-Ink4a-Arf+/+ mice failed to develop tumors. These neoplasms bore a striking histologic resemblance to melanomas that arise in the Tyr-vHRAS/Ink4a-Arf-/- context and often expressed melanocyte differentiation marker Tyrp1, thus supporting their melanocytic origination. All strains, except wild-type mice, developed pigmented and non-pigmented epidermal-derived keratinocytic cysts, whereas Xpc+/+Ink4a-Arf-/- mice exhibited the greatest propensity for squamous cell carcinoma development. We then screened for NRas, HRas, Kras, and BRaf mutations in tumor tissue and detected a higher frequency of rare Kras(Q61) alterations in tumors from Xpc-/-Ink4a-Arf-/- mice compared with Xpc+/+Ink4a-Arf-/- mice (50% versus 7%, P = 0.033). Taken together, results from this novel UV-inducible melanoma model suggest that NER loss, in conjunction with Ink4a-Arf inactivation, can drive melanoma photocarcinogenesis possibly through signature Kras mutagenesis.
尽管有大量证据表明紫外线辐射与黑色素瘤的肿瘤发生有关，但对这一过程仍缺乏清晰的机制理解。由于INK4a和核苷酸切除修复（NER）途径中的遗传突变会使个体易患黑色素瘤，我们着手测试这样一个假设：通过缺失着色性干皮病C（Xpc）基因来废除NER，会在Ink4a-Arf缺陷背景下加剧黑色素瘤的光致癌作用。在实验中，我们培育出了Xpc和Ink4a-Arf双缺陷的小鼠品系，并对野生型、Xpc-/-Ink4a-Arf+/+、Xpc-/-Ink4a-Arf-/-和Xpc+/+Ink4a-Arf-/-小鼠在出生后第3天给予单次剂量的UVB照射，且未进行额外的化学促进处理。事实上，与Xpc+/+Ink4a-Arf-/-小鼠相比，Xpc-/-Ink4a-Arf-/-小鼠中真皮梭形/上皮样细胞黑色素瘤的发生率显著增加（P = 0.005）；野生型和Xpc-/-Ink4a-Arf+/+小鼠未发生肿瘤。这些肿瘤在组织学上与Tyr-vHRAS/Ink4a-Arf-/-背景下产生的黑色素瘤有显著相似之处，且常表达黑素细胞分化标志物Tyrp1，从而支持了它们的黑素细胞起源。除野生型小鼠外，所有品系都出现了色素沉着和无色素沉着的表皮源性角质形成细胞囊肿，而Xpc+/+Ink4a-Arf-/-小鼠表现出最高的鳞状细胞癌发生倾向。然后我们在肿瘤组织中筛查NRAS、HRas、Kras和BRAF突变，发现与Xpc+/+Ink4a-Arf-/-小鼠相比，Xpc-/-Ink4a-Arf-/-小鼠肿瘤中罕见的Kras（Q61）改变频率更高（50%对7%，P = 0.033）。综上所述，这个新型紫外线诱导的黑色素瘤模型的结果表明，NER缺失与Ink4a-Arf失活共同作用，可能通过标志性的Kras诱变驱动黑色素瘤的光致癌作用。
