Xian W, Rosenberg M P, DiGiovanni J
The University of Texas, MD Anderson Cancer Center, Science Park-Research Division, Smithville 78957, USA.
Oncogene. 1997 Mar 27;14(12):1435-44. doi: 10.1038/sj.onc.1200980.
In recent work we showed that the EGF receptor (EGFr) was activated in tumor promoter treated mouse epidermis (Cell Growth & Differentiation, 6: 1447-1455, 1995). In the present study, we have investigated the possible role of other erbB family members in the process of tumor promotion. Both erbB2 and erbB3, but not erbB4, were expressed in cultured mouse keratinocytes and in mouse epidermis in vivo. In cultured mouse keratinocytes, EGF stimulated rapid tyrosine phosphorylation of erbB2 followed by a time-dependent degradation of erbB2 protein. Furthermore, an increase in erbB2:EGFr heterodimer formation was also induced by EGF. In contrast to the results with erbB2, EGF did not induce tyrosine phosphorylation, the degradation of erbB3, or erbB3:EGFr heterodimer formation in cultured keratinocytes. Further analyses revealed that c-src kinase activity was dramatically elevated in cultured mouse keratinocytes exposed to EGF. In mouse epidermis following multiple treatments with 12-O-tetradecanoylphorbol-13-acetate (TPA), the phosphotyrosine content of erbB2 was significantly elevated in a dose-dependent manner. Concomittantly, erbB2:EGFr heterodimer formation and c-src kinase activity were also elevated in TPA-treated epidermis. Structure-activity relationships with several phorbol ester analogs showed that the elevated phosphorylation of erbB2 in mouse epidermis followed closely with tumor promoting ability. Activation of erbB2 and c-src kinase were also observed in the epidermis of TGF alpha transgenic mice where expression of human TGF alpha was targeted to basal keratinocytes with the human K14 promoter. Collectively, the current data suggest that the activation of erbB2 in phorbol ester treated skin can be explained solely by a mechanism involving elevation of EGFr ligands and activation of the EGFr. In addition, activation of c-src may be an important downstream effector in mouse keratinocytes both in vivo and in vitro, following activation of the EGFr, erbB2, or both.
在最近的研究中，我们发现表皮生长因子受体（EGFr）在肿瘤启动子处理的小鼠表皮中被激活（《细胞生长与分化》，6: 1447 - 1455，1995）。在本研究中，我们调查了其他erbB家族成员在肿瘤促进过程中可能发挥的作用。erbB2和erbB3在培养的小鼠角质形成细胞和体内的小鼠表皮中均有表达，而erbB4则不表达。在培养的小鼠角质形成细胞中，表皮生长因子（EGF）刺激erbB2迅速发生酪氨酸磷酸化，随后erbB2蛋白出现时间依赖性降解。此外，EGF还诱导erbB2:EGFr异二聚体形成增加。与erbB2的结果相反，EGF在培养的角质形成细胞中未诱导erbB3的酪氨酸磷酸化、erbB3降解或erbB3:EGFr异二聚体形成。进一步分析表明，暴露于EGF的培养小鼠角质形成细胞中，c-src激酶活性显著升高。在用12 - O - 十四烷酰佛波醇 - 13 - 乙酸酯（TPA）多次处理后的小鼠表皮中，erbB2的磷酸酪氨酸含量以剂量依赖方式显著升高。同时，在TPA处理的表皮中，erbB2:EGFr异二聚体形成和c-src激酶活性也升高。与几种佛波酯类似物的构效关系表明，小鼠表皮中erbB2磷酸化水平的升高与肿瘤促进能力密切相关。在人转化生长因子α（TGFα）转基因小鼠的表皮中也观察到erbB2和c-src激酶的激活，其中人TGFα的表达通过人K14启动子靶向基底角质形成细胞。总体而言，目前的数据表明，佛波酯处理皮肤中erbB2的激活可能仅由涉及EGFr配体升高和EGFr激活的机制来解释。此外，在体内和体外，EGFr、erbB2或两者激活后，c-src的激活可能是小鼠角质形成细胞中的一个重要下游效应器。
