Juxtacrine Growth Control with HB-EGF Complex

HB-EGF是EGF家族生长因子家族的一员。膜锚固型HB-EGF(proHB-EGF)不仅是可溶性HB-EGF的前体，也是具有生物活性的分子。Prohib-EGF与其他膜蛋白形成复合体。CD9和硫酸肝素蛋白多糖(S)与前Hb-EGF结合并调节其生物学活性。ProHB-EGF还与整合素α3β1形成复合体。免疫荧光染色研究表明，由proHB-EGF、CD9和整合素α3beta1组成的复合体共定位于细胞-细胞接触部位，提示ProHB-EGF复合体以旁分泌的方式在细胞间通讯中发挥作用。为了了解proHB-EGF复合体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)CD9CD9上调proHB-EGF的活性，上调proHB-EGF的生物学活性。2)ProHB-EGF的生长抑制活性。因此，可溶性形式和膜锚定形式对细胞生长控制具有不同的生物学活性。3)CD9缺失小鼠CD9的分析将在连接proHB-EGF和整合素α3beta1方面发挥关键作用。为了分析proHB-EGF复合体的生理作用，建立了CD9缺失小鼠。CD9基因缺失的小鼠出生后看起来很健康，但表现出严重的生殖系统缺陷。进一步的研究目前正在进行中。

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.