The role of membrane-anchored HB-EGF on cell growth

HB-EGF是EGF家族生长因子中的一员。膜锚定形式的HB-EGF （proHB-EGF）也被认为是白喉毒素受体。因此，该蛋白一方面是一种膜锚定生长因子，另一方面是细菌毒素的特异性受体。Klagsbrun博士在细胞培养基中发现了HIB-EGF，并研究了HB-EGF可溶性形式的生物活性，而Mekada则研究了proHB-EGF作为白喉毒素受体。这次联合会议的目的是研究proHB-EGF在细胞生长和发育过程中的生理作用。ProHB-EGP与其他膜蛋白形成复合物。CD9和硫酸肝素蛋白聚糖与proHB-EGF结合并调节其生物活性。ProHB-EGF也与integrinalpha3beta1形成复合物。免疫荧光染色研究表明，由proHB-EGF、CD9和integrin# 3beta1组成的复合物在细胞-细胞接触部位共定位，表明proHB-EGF复合物以近距离的方式参与细胞间通讯。为了了解proHB-EGF复合物在细胞间通讯中的生理作用，我们做了以下研究，得到以下结果：1)CD9上调proHB-EGF活性：CD9上调proHB-EGF的生物活性。确定了CD9和proHB-EGF中上调所需的区域。2) proHB-EGF的生长抑制活性：我们观察到，在可溶形式的HB-EGF和EGF刺激细胞生长的培养条件下，proHB-EGF通过近碱机制表现出生长抑制活性。因此，可溶性形式和膜固定形式对细胞生长具有不同的生物活性。3) CD9缺失小鼠分析：CD9可能在proHB-EGF与integrinalpha3beta1的连接中起关键作用。为了分析proHB-EGF复合物的生理作用，我们制备了CD9小鼠。CD9缺失小鼠出生后健康，但生殖系统出现严重缺陷。进一步的研究正在进行中。少

HB-EGF is a member of EGF family growth factors. The membrane-anchored form of HB- EGF (proHB-EGF) is also known to be a diphtheria toxin receptor. Therefore this protein is a kind of membrane-anchored growth factors in one hand, the specific receptor of the bacteria toxin in the other hand. Dr. Klagsbrun identified HIB-EGF in the cell culture medium and studied biological activities of the soluble form of HB-EGF, while Mekada have studied proHB-EGF as the diphtheria toxin receptor. The aim of this joint meeting is to examine the physiological roles of proHB-EGF in cell growth and developmental processes.ProHB-EGP forms a complex with other membrane proteins. CD9 and heparan-sulfate proteoglycan(s) associate with proHB-EGF and modulate its biological activities. ProHB-EGF also forms a complex with integrincalpha3beta1. Studies by immunofluorescence staining showed that the complex cornprised of proHB-EGF, CD9 and integrina#3beta1 co-localizes at cell-cell contact sites, suggesting that … More the proHB-EGF complex plays a role in intercellular communication in a juxtacrine manner. In order to know the physiological role of the proHB-EGF complex in a intercellular communication, we have done the following studies and got the results as follows :1)Upregulation of proHB-EGF activity by CD9 : CD9 upregulates the biological activities of proHB-EGF.Regions in both CD9 and proHB-EGF necessary for the upregulation were determined.2)Growth inhibitory activity of proHB-EGF : We have observed that proHB-EGF shows growth inhibitory activity by juxtacrine mechanism under the culture conditions which soluble forms of HB-EGF and EGF stimulate cell growth. Thus, it is suggested that the soluble form and the membrane-anchored form have different biological activities for cell growth control.3)Analysis of CD9 null mice : CD9 would have a key role to connect proHB-EGF with integrinalpha3beta1 . To analyze the physiological role of proHB-EGF complex CD9 null mice were generated. CD9 null mice were born and seem healthy, but showed severe defect in reproductive system. Further studies are now in progress. Less