Ashida Atsuko, Takata Minoru, Murata Hiroshi, Kido Kenji, Saida Toshiaki
Department of Dermatology, Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto 390-8621, Japan.
Int J Cancer. 2009 Feb 15;124(4):862-8. doi: 10.1002/ijc.24048.
Recent studies showed KIT gene aberrations in a substantial number of melanomas on acral skin and mucosa, suggesting the therapeutic benefit of tyrosine kinase inhibitors, such as imatinib. We therefore examined the expression and mutations of KIT in 4 primary and 24 metastatic acral and mucosal melanomas. Immunohistochemistry revealed moderate or strong KIT protein expression in 13 (48%) tumors. Sequence analysis revealed K642E and D820Y mutations in two metastases. Amplification of KIT was identified by real-time PCR in 4 tumors, including one that had K642E. Western blot analysis showed phosphorylation of the KIT receptor in 8 (62%) of 13 cryopreserved samples, indicating the frequent pathological activation of the receptor in vivo. Phosphorylation of KIT protein was detected in 2 tumors harboring KIT mutations, as well as in one tumor with KIT gene amplification. Furthermore, 5 tumors without detectable KIT gene aberrations showed phosphorylation of the KIT receptor. Expression of stem cell factor (SCF) in melanoma cells as well as stromal cells suggests SCF/KIT autocrine and paracrine activation in these tumors. Finally, we found significant growth suppressive effects of sunitinib in two acral melanoma cell lines; one harboring the D820Y mutation and one showing SCF-dependent KIT activation. These results show pathological activation of KIT in a substantial number of metastatic tumors of acral and mucosal melanomas, and suggest a potential therapeutic benefit of sunitinib for these melanomas.
近期研究显示，大量肢端皮肤和黏膜黑色素瘤存在KIT基因畸变，提示酪氨酸激酶抑制剂（如伊马替尼）具有治疗益处。因此，我们检测了4例原发性以及24例转移性肢端和黏膜黑色素瘤中KIT的表达及突变情况。免疫组化显示，13例（48%）肿瘤中有中度或强KIT蛋白表达。序列分析在2例转移灶中发现了K642E和D820Y突变。通过实时PCR在4例肿瘤中鉴定出KIT扩增，其中1例存在K642E突变。蛋白质印迹分析显示，在13份冻存样本中的8例（62%）检测到KIT受体磷酸化，表明该受体在体内频繁发生病理激活。在2例携带KIT突变的肿瘤以及1例存在KIT基因扩增的肿瘤中检测到KIT蛋白磷酸化。此外，5例未检测到KIT基因畸变的肿瘤也显示出KIT受体磷酸化。黑色素瘤细胞以及基质细胞中干细胞因子（SCF）的表达提示这些肿瘤中存在SCF/KIT自分泌和旁分泌激活。最后，我们发现舒尼替尼对2株肢端黑色素瘤细胞系具有显著的生长抑制作用；1株携带D820Y突变，另1株显示SCF依赖性KIT激活。这些结果表明，大量肢端和黏膜黑色素瘤转移瘤中存在KIT的病理激活，并提示舒尼替尼对这些黑色素瘤具有潜在的治疗益处。
