Yu Hong, McDaid Ronan, Lee John, Possik Patricia, Li Ling, Kumar Suresh M, Elder David E, Van Belle Patricia, Gimotty Phyllis, Guerra Matt, Hammond Rachel, Nathanson Katharine L, Dalla Palma Maria, Herlyn Meenhard, Xu Xiaowei
Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, 3400 Spruce Street, Philadelphia, PA 19104, USA.
Am J Pathol. 2009 Jun;174(6):2367-77. doi: 10.2353/ajpath.2009.081057. Epub 2009 Apr 23.
Melanocytic nevi frequently harbor oncogenic BRAF mutations, but only a minority progress to melanoma. In human melanocytes, persistent BRAF(V600E) expression triggers oncogene-induced senescence, which implies that bypass of oncogene-induced senescence is necessary for malignant transformation of melanocytes. We show that a subpopulation of primary human melanocytes with persistent expression of BRAF(V600E) do not enter oncogene-induced senescence, but instead survive despite heightened MAPK activity. Disruption of the p53 pathway using short-hairpin RNA initiated rapid growth of these V600E(+) melanocytes in vitro. The resultant V600E(+)/p53(sh) melanocytes grew anchorage-independently in soft agar, formed pigmented lesions reminiscent of in situ melanoma in artificial skin reconstructs, and were weakly tumorigenic in vivo. Array comparative genomic hybridization analysis demonstrated that the transformed melanocytes acquired a substantial deletion in chromosome 13, which encodes the Rb1 tumor suppressor gene. Gene expression profiling study of nevi and melanomas showed that p53 target genes were differentially expressed in melanomas compared with nevi, suggesting a dysfunctional p53 pathway in melanoma in vivo. In summary, these data demonstrate that a subpopulation of melanocytes possesses the ability to survive BRAF(V600E)-induced senescence, and suggest that p53 inactivation may promote malignant transformation of these cells.
黑素细胞痣常常携带致癌性BRAF突变，但只有少数会进展为黑色素瘤。在人类黑素细胞中，持续的BRAF（V600E）表达会引发癌基因诱导的衰老，这意味着黑素细胞的恶性转化需要绕过癌基因诱导的衰老。我们发现，持续表达BRAF（V600E）的原代人类黑素细胞亚群不会进入癌基因诱导的衰老，而是尽管MAPK活性增强仍能存活。使用短发夹RNA破坏p53通路会引发这些V600E（+）黑素细胞在体外快速生长。产生的V600E（+）/p53（sh）黑素细胞在软琼脂中可独立于锚定生长，在人工皮肤重建物中形成类似于原位黑色素瘤的色素沉着病变，并且在体内具有弱致瘤性。阵列比较基因组杂交分析表明，转化的黑素细胞在13号染色体上出现了大量缺失，该染色体编码Rb1肿瘤抑制基因。痣和黑色素瘤的基因表达谱研究表明，与痣相比，p53靶基因在黑色素瘤中差异表达，提示体内黑色素瘤中p53通路功能失调。总之，这些数据表明黑素细胞亚群具有在BRAF（V600E）诱导的衰老中存活的能力，并提示p53失活可能促进这些细胞的恶性转化。
