Juxtacrine stimulation of cellular communication by HB-EGF.

我们发现，肝素结合EGF样生长因子（proHB-EGF）的膜锚定形式具有促有丝分裂活性。ProHB-EGF与四跨膜蛋白CD 9结合。CD 9可增强proHB-EGF的促有丝分裂活性，并与整合素α 3 β 1形成复合物。本研究的目的是了解这种复合物的生理作用。我们做了几个实验，得到了以下结果。(1)使用特异性抗体proHB-EGF、CD 9、整合素α 3和整合素β 1，通过免疫荧光研究了源自猴肾的复合Vero细胞的定位。结果显示，proHB-EGF、CD 9和整合素α 3b 1定位于细胞-细胞连接区。(2)肝素结合结构域（KBD）的作用为了分析HBD结构域在proHB-EGF中的作用，制备了proHB-EGF的HBD缺失突变体。结果表明，HBD对促有丝分裂活性和白喉毒素结合活性不是必需的。硫酸乙酰肝素蛋白多糖可能通过与proHB-EGF的HBD结构域相互作用来调节proHB-EGF的促有丝分裂活性，提示proHB-EGF可能在一个大的复合体中起细胞-细胞相互作用的作用。

We have found that the membrane-anchored form of heparin-binding EGF-like growth factor (proHB-EGF) has a juxtacrine mitogenic activity. ProHB-EGF associates with tetramembrane-spanning protein CD9. CD9 was found to enhance the juxtacrine mitogenic activity of proHB-EGF.Furthermore, proHB-EGF forms a complex with integrin alpha3beta1. The aim of this study is to understand the physiological role of this complex. We have done sevaral experiments and obtained the following results.(1) Localization of the complexVero cell, derived from monkey kidney, was studied by immunofluorescence using specific antibodies to proHB-EGF,CD9, integrin alpha3, and integrin beta1. The results revealed that proHB-EGF,CD9 and integrin alpha3b1 localized at cell-cell junction region.(2) The role of heparin-binding domain (KBD)To analyze the role of HBD domain of proHB-EGF,the deletion mutants of HBD of proHB-EGF were produced. The results showed that HBD is not essential for the mitogenic activity and diphtheria toxin binding activity. Heparansulfate proteoglycans may modulate the mitogenic activity of proHB-EGF by interacting with the HBD domain of proHB-EGF.These results indicate that proHB-EGF may play the role of cell-cell interaction in a large complex.