Juxtacrine Growth Control with HB-EGF Complex

HB-EGF是EGF家族生长因子中的一员。膜锚定形式的HB-EGF （proHB-EGF）不仅是可溶形式HB-EGF的前体，而且是具有生物活性的分子。禁止- egf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形成复合体。免疫荧光染色研究表明，由proHB-EGF、CD9和integrinalpha3beta1组成的复合物共定位于细胞-细胞接触部位，提示prohibition - 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，得到如下结果：1)CD9CD9上调proHB-EGF活性，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通过近胞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缺失小鼠的分析ecd9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。

HB-EGF is a member of EGF family growth factors. The membrane-anchored form of HB-EGF (proHB-EGF) is not only precursor of the soluble form of HB-EGF but also biologically active molecule. ProHIB-EGF 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 integrinalpha3beta1. Studies by immunofluorecence staining showed that the complex comprised of proHB-EGF, CD9 and integrinalpha3beta1 co-localizes at cell-cell contact sites, suggesting that the proHIB-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 CD9CD9 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-EGFWe 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 miceCD9 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.