EGF MEDIATED SIGNAL TRANSDUCTION THROUGH COEXPRESSED ERBB2 AND ERBB3 RECEPTORS

白介素3(IL-3)依赖的小鼠32D细胞不能检测到 表达表皮生长因子受体(EGFR)，不增殖 作为对EGF、HERG或其他已知的EGF样配体的反应。 在这里，我们报告了EGF特异性地与之结合并且可以被交联 至32D共表达ErbB2和ErbB3的转基因细胞(32D.E2/E3)，但不 分别表达ErbB2或ErbB3的转染体。 [125I]在32D.E2/E3细胞中检测到的EGF交联物 被HRG和贝塔细胞蛋白(BTC)取代，但不被其他EGF样物取代 被分析的配基。EGF、BTC和HRG也可诱导受体 酪氨酸磷酸化，激活下游信号分子 32D.E_2/E_3细胞增殖。32D转染体也得到了 产生了单独表达ErbB3-EGFR嵌合体的(32D.E3-E1)或 与ErbB2(32D.E2/E3-E1)联合应用。而HRG刺激32D.E3- E1细胞DNA合成和受体磷酸化，EGF和 BTC处于非活动状态。然而，EGF和BTC与HRG一样有效。 ErbB2与嵌合体共表达时的信号传导 32D.E_2/E3-E_1转染体。这些结果提供了证据： EGF和BTC的ERBB2/ErbB3结合位点是由先前的 未描述的机制需要两个不同的共同表达 感受器。使用MDAMB134人乳腺癌的附加数据 在没有EGFR的情况下自然表达ErbB2和ErbB3的细胞， 支持使用32D细胞获得的结果，并表明EGF 而BTC可能有助于共表达的癌症的进展 ErbB2和ErbB3。

Interleukin-3 (IL-3)-dependent murine 32D cells do not detectably express epidermal growth factor receptors (EGFRs) and do not proliferate in response to EGF, heregulin (HRG) or other known EGF-like ligands. Here, we report that EGF specifically binds to and can be crosslinked to 32D transfectants co-expressing ErbB2 and ErbB3 (32D.E2/E3), but not to transfectants expressing either ErbB2 or ErbB3 individually. [125I]EGF- crosslinked species detected in 32D.E2/E3 cells were displaced by HRG and betacellulin (BTC) but not by other EGF-like ligands that were analyzed. EGF, BTC and HRG also induced receptor tyrosine phosphorylation, activation of downstream signaling molecules and proliferation of 32D.E2/E3 cells. 32D transfectants were also generated which expressed an ErbB3-EGFR chimera alone (32D.E3-E1) or in combination with ErbB2 (32D.E2/E3-E1). While HRG stimulation of 32D.E3- E1 cells resulted in DNA synthesis and receptor phosphorylation, EGF and BTC were inactive. However, EGF and BTC were as effective as HRG in mediating signaling when ErbB2 was co-expressed with the chimera in the 32D.E2/E3-E1 transfectant. These results provide evidence that ErbB2/ErbB3 binding sites for EGF and BTC are formed by a previously undescribed mechanism that requires co-expression of two distinct receptors. Additional data utilizing MDA MB134 human breast carcinoma cells, which naturally express ErbB2 and ErbB3 in the absence of EGFRs, supported the results obtained employing 32D cells and suggest that EGF and BTC may contribute to the progression of carcinomas that co-express ErbB2 and ErbB3.