Purushotham K R, Nakagawa Y, Kurian P, Patel R, Crews F T, Humphreys-Beher M G
Department of Oral Biology, University of Florida, Gainesville.
Biochim Biophys Acta. 1993 Jul 28;1178(1):40-8. doi: 10.1016/0167-4889(93)90107-z.
We have recently shown that beta-adrenergic agonist, isoproterenol-induced parotid acinar cell proliferation is in part mediated by elevated levels of surface galactosyltransferase which undergoes interaction with the EGF-R. The receptor subsequently undergoes autophosphorylation on the tyrosine residues in a manner similar to its 'receptor-ligand' interaction (Purushotham et al. (1992) Biochem. J. 284, 767-776). In this study, we provide evidence for phosphatidylinositol 3-kinase and 4-kinase as cytoplasmic signalling proteins involved in both the isoproterenol and EGF-stimulated signal transduction upon in vitro and in-vivo stimulation of parotid acinar cells. Total cell lysate activity for the PtdIns 4-kinase was 2- and 3-fold higher than unstimulated control cells, while the PtdIns 3-kinase was 1.4- and 2.8-fold higher following stimulation by isoproterenol or EGF, respectively. Increases of 6- and 2-fold in phosphatidylinositol 3-kinase were observed in anti-phosphotyrosine-antibody-immunoprecipitated cell lysates upon in-vitro growth stimulation with isoproterenol or EGF, respectively. There was an increase in tyrosine phosphorylation of the holoenzyme and association of the p85 subunit of phosphatidylinositol 3-kinase with EGF-R in response to both isoproterenol and EGF treatments. This corresponded with the mobilization of p85 from the cytoplasm to the plasma membrane upon growth stimulation. These results further implicate the phosphoinositide metabolites in the second messenger signalling pathways of isoproterenol-induced rat parotid cell proliferation. The parallel utilization of EGF indicate that the post-transductional mechanisms of isoproterenol-induced acinar cell proliferation are similar to the growth-factor-mediated activation of intracellular signalling pathways for cell growth.
我们最近发现，β-肾上腺素能激动剂异丙肾上腺素诱导的腮腺腺泡细胞增殖部分是由表面半乳糖基转移酶水平升高介导的，该酶与表皮生长因子受体（EGF-R）相互作用。随后，该受体以类似于其“受体-配体”相互作用的方式在酪氨酸残基上发生自身磷酸化（Purushotham等人，（1992年）《生物化学杂志》284卷，767 - 776页）。在本研究中，我们提供证据表明磷脂酰肌醇3激酶和4激酶作为细胞质信号蛋白，参与了体外和体内刺激腮腺腺泡细胞时异丙肾上腺素和表皮生长因子（EGF）刺激的信号转导。磷脂酰肌醇4激酶的总细胞裂解物活性比未刺激的对照细胞高2倍和3倍，而磷脂酰肌醇3激酶在分别用异丙肾上腺素或EGF刺激后比对照细胞高1.4倍和2.8倍。在用异丙肾上腺素或EGF进行体外生长刺激后，分别在抗磷酸酪氨酸抗体免疫沉淀的细胞裂解物中观察到磷脂酰肌醇3激酶增加了6倍和2倍。响应异丙肾上腺素和EGF处理，全酶的酪氨酸磷酸化增加，并且磷脂酰肌醇3激酶的p85亚基与EGF-R结合。这与生长刺激后p85从细胞质转移到质膜相对应。这些结果进一步表明磷酸肌醇代谢产物参与了异丙肾上腺素诱导的大鼠腮腺细胞增殖的第二信使信号通路。EGF的平行利用表明，异丙肾上腺素诱导的腺泡细胞增殖的转导后机制类似于生长因子介导的细胞生长细胞内信号通路的激活。
