Several cAMP-elevating agents such as cholera toxin (CT), forskolin and 3-isobutyl-1-methylxanthine (IBMX) exhibited weak mitogenic activity on bovine undifferentiated mammary epithelial cells in three-dimensional collagen culture. CT and IBMX strongly synergized with epidermal growth factor (EGF), insulin-like growth factor I (IGF-I) or both, but not with 10% fetal calf serum (FCS). Permeable cAMP analogs also synergized with IGF-I. Other hormones such as ovine prolactin, bovine growth hormone, estrogen or progesterone were not mitogenic and not synergistic with EGF, IGF-I, CT and FCS. Pertussis toxin (PT) reduced the DNA synthesis in cells cultured in the basal medium and attenuated 40-90% of the mitogenic activity stimulated by 10% FCS. PT inhibition of DNA synthesis was accompanied by ADP-ribosylation of 40 kDa and 41 kDa membrane proteins. The 41 kDa protein cross-reacted with antibodies that recognize the Gi-protein of the adenylate cyclase system, indicating the involvement of the latter in the mitogenic process. The nature of the second protein remains unknown. The present results suggest that the mitogenesis of normal mammary epithelial cells which is stimulated by IGF-I, EGF and other factors found in FCS is mediated through both cAMP-dependent and independent pathways. These pathways include PT-sensitive GTP-binding proteins.

译文

:几种cAMP增强剂,例如霍乱毒素(CT),毛喉素和3-异丁基-1-甲基黄嘌呤(IBMX)在三维胶原蛋白培养物中对牛未分化乳腺上皮细胞显示出弱的促有丝分裂活性。 CT和IBMX与表皮生长因子(EGF),胰岛素样生长因子I(IGF-I)或两者均具有强效协同作用,但与10%的胎牛血清(FCS)没有协同作用。渗透性cAMP类似物也与IGF-I协同作用。其他激素,例如绵羊催乳激素,牛生长激素,雌激素或孕激素,没有促有丝分裂作用,也不与EGF,IGF-I,CT和FCS协同作用。百日咳毒素(PT)减少了在基础培养基中培养的细胞中的DNA合成,并减弱了10%FCS刺激的有丝分裂活性的40-90%。 PT对DNA合成的抑制作用伴随着40 kDa和41 kDa膜蛋白的ADP-核糖基化。 41 kDa蛋白与识别腺苷酸环化酶系统的Gi蛋白的抗体发生交叉反应,表明后者参与了促有丝分裂过程。第二种蛋白质的性质仍然未知。目前的结果表明,通过IGF-I,EGF和FCS中发现的其他因素刺激的正常乳腺上皮细胞的有丝分裂是通过cAMP依赖性和独立途径介导的。这些途径包括PT敏感的GTP结合蛋白。

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