Hewitt Chelsee, Lee Wu Chu, Evans Gareth, Howell A, Elles Robert G, Jordan Richard, Sloan Philip, Read Andrew P, Thakker Nalin
University of Manchester Department of Medical Genetics and Regional Genetic Service, Central Manchester Healthcare Trust, St. Mary's Hospital, Manchester, M13 OJH, UK.
Hum Mol Genet. 2002 May 15;11(11):1273-9. doi: 10.1093/hmg/11.11.1273.
Familial melanoma predisposition is associated with germline mutations at the CDKN2A/ARF locus in up to 40% of families. The exact role of the two proteins encoded by this complex locus in this predisposition is unclear. Most mutations affect either CDKN2A only or products of both genes. Recently a deletion affecting ARF-specific exon 1beta was reported in a family with melanoma and neural tumours. However, the possibility of this deletion also altering the CDKN2A transcript could not be excluded. More convincingly, a 16 base pair insertion in exon 1beta has been reported in an individual with multiple melanomas suggesting a direct role for ARF in melanoma predisposition. We report here a splice mutation in exon 1beta in a family with melanoma that results in ARF haploinsufficiency. The mutation was observed in a mother and daughter with melanoma. A sibling of the mother with breast cancer also had this mutation. Analysis of the melanoma from one individual revealed a 62 bp deletion in exon 3 of the wildtype allele and loss of the mutant allele; these somatic changes would affect both CDKN2A and ARF. These somatic events suggest that concomitant inactivation of both ARF and CDKN2A may be necessary for melanoma development and that mutations in ARF and CDKN2A possibly confer different levels of susceptibility to melanoma, with the former associated with lesser predisposition. In this situation, the events follow a 'three-hit' model as observed in tumours from FAP patients with an attenuated phenotype. Overall, the data suggest a direct role for ARF haploinsufficiency in melanoma predisposition and co-operation between ARF and CDKN2A in tumour formation, consistent with recent observations in Cdkn2a-specific knockout mice.
在高达40%的家族中，家族性黑色素瘤易感性与CDKN2A/ARF基因座的种系突变相关。该复合基因座编码的两种蛋白质在这种易感性中的确切作用尚不清楚。大多数突变仅影响CDKN2A或两个基因的产物。最近，在一个患有黑色素瘤和神经肿瘤的家族中报道了影响ARF特异性外显子1β的缺失。然而，不能排除这种缺失也改变CDKN2A转录本的可能性。更有说服力的是，在一个患有多发性黑色素瘤的个体中报道了外显子1β中的16个碱基对插入，提示ARF在黑色素瘤易感性中起直接作用。我们在此报告一个患有黑色素瘤的家族中外显子1β的剪接突变，该突变导致ARF单倍体不足。在患有黑色素瘤的母亲和女儿中观察到该突变。母亲患有乳腺癌的一个兄弟姐妹也有这种突变。对一名个体的黑色素瘤分析显示，野生型等位基因外显子3中有62 bp缺失，突变等位基因丢失；这些体细胞变化将影响CDKN2A和ARF。这些体细胞事件表明，ARF和CDKN2A的同时失活可能是黑色素瘤发生所必需的，并且ARF和CDKN2A中的突变可能赋予对黑色素瘤不同程度的易感性，前者与较低的易感性相关。在这种情况下，这些事件遵循在具有减弱表型的FAP患者的肿瘤中观察到的“三次打击”模型。总体而言，数据表明ARF单倍体不足在黑色素瘤易感性中起直接作用，并且ARF和CDKN2A在肿瘤形成中相互协作，这与最近在Cdkn2a特异性敲除小鼠中的观察结果一致。
