Joint Study on the Tumorigenicity of HGF and c-met Receptor

肝细胞生长因子(HGF)是一种多效性因子，可作为多种上皮细胞的有丝分裂原、运动原和形态原。C-Met原癌基因产物被确定为HGF的受体。在本研究中，我们分析了HGF和c-Met受体的致瘤性。多种肉瘤细胞株均表达高水平的c-Met受体，提示HGF-Met自分泌信号在肉瘤的发生过程中起重要作用。HGF转换酶是一种由65 kDa的重链和32 kDa的轻链组成的异二聚体蛋白，它能将失活的单链前体HGF转化为活性的双链HGF。合成的多肽衍生物Ac-Lys-Gln-Leu-Arg-氯甲基酮具有较强的抑制HGF转换酶活性和促有丝分裂活性的作用，但该抑制物不能抑制肉瘤细胞的生长，可能与其在条件培养液中的不稳定性有关。以鸡c-SEA酪氨酸激酶基因(与c-Met密切相关的基因)为探针，获得了编码c-SEA、Sky和LIMK三种新的蛋白激酶的cDNA。c-SEA与c-Met受体高度相关，可能是HGF相关生长因子的受体。SKY是一种与Ax1/UFO/Ark相关的新型受体酪氨酸激酶。确定c-Sea和Sky的配体是正在进行的研究的主题。LIMK是一种细胞质丝氨酸/苏氨酸激酶，在N端含有两个重复的LIM/双锌指基序，在C端含有一个蛋白激活域。LIMK可能通过与其他含LIM的蛋白质相互作用而参与肿瘤发生过程。

Hepatocyte growth factor (HGF) is a pleiotropic factor, which act as a mitogen, motogen, and morphogen for various epithelial cells. The c-Met protooncogene product was identified as the receptor for HGF.In this study, we analyzed the tumorigenicity of HGF and c-Met receptor. Various sarcoma cell lines were found to express high level of c-Met receptor, indicating that the HGF-Met autocrine signaling contributes to the tumorigenic process of sarcoma.HGF converting enzyme, which converts an inactive single-chain precursor (pro-HGF) to a two-chain active form HGF,was purified and identified as a heterodimer protein composed of a 65-kDa heavy chain and a 32-kDa light chain. A synthetic peptide derivative, Ac-Lys-Gln-Leu-Arg-chloromethylketone, containing the sequence of pro-HGF cleavage site strongly inhibited the converting enzyme activity, and the mitogenic activity of pro-HGF.However, this inhibitor could not block the growth of sarcoma cells, probably because of the instability in the conditioned medium. Using the chicken c-sea tyrosine kinase gene (the gene closely related to c-Met) as a probe, we obtained the cDNAs encoding three novel protein kinases, c-Sea, Sky and LIMK.c-Sea is highly related to the c-Met receptor and seems to be a receptor for a HGF-related growth factor. Sky is a novel receptor tyrosine kinase related to Axl/Ufo/Ark. Identification of the ligands for c-Sea and Sky is the subject of ongoing studies. LIMK is a cytoplasmic serine/threonine kinase containing two repeats of LIM/double zinc finger motif at the N-terminus and a protein kinase domain at the C-terminus. LIMK may be involved in the oncogenic process through interactions with other LIM-containing proteins.