Analysis of the expression and roles of receptor-type tyrosine kinase in keloid tissue

瘢痕疙瘩是一种病因不明的真皮纤维增生性组织。蛋白酪氨酸激酶(PTKs)在调节细胞生长和分化中起着重要作用。在瘢痕疙瘩成纤维细胞中，PTK通路的激活被认为与细胞的异常增殖和迁移密切相关，为了检测正常和瘢痕疙瘩成纤维细胞中受体类型PTK的表达，我们采用了同源克隆的方法。虽然8个受体类型的PTK基因在两种成纤维细胞中都有表达，但胰岛素样生长因子-I受体(IGF-IR)仅在瘢痕疙瘩成纤维细胞中过表达。免疫组织化学分析证实了IGF-IR的高表达。为了检测IGF-I/IGF-IR通路的功能特性，我们研究了两种类型的成纤维细胞的细胞增殖、侵袭活性和凋亡。与血清刺激相比，IGF-I对两种成纤维细胞的促有丝分裂作用都很弱。相反，在IGF-I存在下，瘢痕疙瘩成纤维细胞的侵袭活性显著增加，并被抗IGF-IR的中和抗体抑制。瘢痕疙瘩成纤维细胞也能抵抗C2-神经酰胺诱导的细胞凋亡。外源性添加IGF-I可增强瘢痕疙瘩成纤维细胞对神经酰胺诱导的细胞凋亡的抵抗力。磷脂酰肌醇3-激酶(PI3-K)抑制剂Wortmannin抑制了IGF-I对瘢痕疙瘩成纤维细胞的抗凋亡作用，提示激活的IGF-I/IGF-IR信号可能通过增强成纤维细胞的侵袭活性和抗凋亡能力而参与瘢痕疙瘩的发病过程。

Keloid is a dermal fibroproliferative tissue of unknown etiology. Protein tyrosine kinases (PTKs) play an important role in the regulation of cell growth and differentiation. Activation of PTK cascade in keloid fibroblasts is thought to be closely linked to abnormal cell proliferation and migration.In order to examine the expression of receptor-type PTK in normal and keloid fibroblasts, we used the homology cloning method with a degenerated primer. Although 8 receptor-type PTK genes were expressed in both fibroblasts, insulin-like growth factor-I receptor (IGF-IR) was overexpressed only in keloid fibroblasts. Immunohistochemical analysis confirmed the high expression of IGF-IR.To examine the functional properties of the IGF-I/IGF-IR pathway, we investigated cell proliferation invasion activity and apoptosis of both types of fibroblasts. The mitogenic effect of IGF-I on both fibroblasts was very weak compared with serum stimulation. In contrast, the invasive activity of keloid fibroblasts was markedly increased in the presence of IGF-I, and inhibited by a neutralizing antibody against IGF-IR. Also keloid fibroblasts resisted apoptosis induced by C2-ceramide. Exogenously added IGF-I enhanced the resistance of keloid fibroblasts to ceramide-induced apoptosis. Wortmannin, a phosphatidylinositol 3-kinase (PI3-K) inhibitor suppressed the anti-apoptotic action of IGF-I in keloid fibroblasts.These findings suggest that the involvement of activated IGF-I/IGF-IR signal in the pathogenesis of keloid by enhancing the invasive activity and the resistance to apoptosis of fibroblasts.