Mau S E, Saermark T, Vilhardt H
Department of Medical Physiology, University of Copenhagen, Denmark.
Endocrinology. 1997 Apr;138(4):1704-11. doi: 10.1210/endo.138.4.5072.
We have investigated cross-talk between the cAMP/protein kinase A (PKA) and protein kinase C (PKC)/inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) messenger systems probed by vasoactive intestinal peptide (VIP) and substance P (SP), respectively, in rat pituitary cell cultures enriched in lactotrophs. VIP and forskolin had no effect on the basal distribution pattern of the four PKC isozymes (alpha, beta, delta, and zeta) detectable in lactotroph-enriched cell cultures derived from peripubertal male rats, whereas both compounds significantly increased translocation of PKC alpha and beta from the cytosol to the plasma membrane induced by SP. The delta and zeta subspecies were not affected by VIP and forskolin. Moreover, VIP and forskolin also stimulated SP-induced formation of Ins(1,4,5)P3 while having no effect on basal inositol phosphate turnover. The effects of VIP and forskolin on PKC isozyme distribution could be blocked by pretreating cells with the PKA inhibitor rp-cAMP. On the other hand, SP potentiated the effect of VIP and forskolin on cAMP formation while having no effect on the cAMP pathway when it was not triggered by an appropriate agonist. Down-regulation of PKC activity by long term 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment (24 h) diminished, but did not abolish, the effect of SP on VIP-stimulated cAMP production. Staurosporine and dopamine inhibited the potentiating effect of SP on cAMP accumulation. TPA, which translocates PKC alpha, beta, and delta in lactotrophs, had a synergistic effect on cAMP formation induced by VIP, but did also, unlike SP, display cAMP rising abilities when cells were not exposed to VIP and forskolin. Discharging intracellular Ca2+ by thapsigargin pretreatment had no effect on the basal cAMP concentration or the VIP-induced cAMP response, whereas exposure of cells to SP, thapsigargin, and VIP resulted in a decrease of the cAMP response compared with SP + VIP. The potentiating effect of SP on the VIP response could also be inhibited, but not blocked, by staurosporine. On the basis of these results, it is concluded that there exists substantial cross-talk between the cAMP/PKA and PKC/Ins(1,4,5)P3 messenger systems in lactotroph-enriched cell cultures. Key effectors seem to be PKA, one or more of PKC alpha, beta, deleta and Ins(1,4,5)P3-sensitive Ca2+ stores.
我们分别用血管活性肠肽（VIP）和P物质（SP）研究了富含催乳素细胞的大鼠垂体细胞培养物中，环磷酸腺苷/蛋白激酶A（PKA）和蛋白激酶C（PKC）/肌醇1,4,5-三磷酸（Ins(1,4,5)P3）信使系统之间的相互作用。VIP和福斯高林对从青春期前雄性大鼠获得的富含催乳素细胞的培养物中可检测到的四种PKC同工酶（α、β、δ和ζ）的基础分布模式没有影响，而这两种化合物均显著增加了由SP诱导的PKCα和β从细胞质向质膜的转位。δ和ζ亚型不受VIP和福斯高林的影响。此外，VIP和福斯高林还刺激了SP诱导的Ins(1,4,5)P3的形成，而对基础肌醇磷酸周转率没有影响。VIP和福斯高林对PKC同工酶分布的影响可通过用PKA抑制剂rp-cAMP预处理细胞来阻断。另一方面，SP增强了VIP和福斯高林对环磷酸腺苷形成的作用，而当它未被适当激动剂触发时，对环磷酸腺苷途径没有影响。通过长期（24小时）12-O-十四烷酰佛波醇13-乙酸酯（TPA）处理下调PKC活性，减少但并未消除SP对VIP刺激的环磷酸腺苷产生的作用。星形孢菌素和多巴胺抑制了SP对环磷酸腺苷积累增强作用。TPA可使催乳素细胞中的PKCα、β和δ转位，它对VIP诱导的环磷酸腺苷形成具有协同作用，但与SP不同的是，当细胞未暴露于VIP和福斯高林时，它也具有升高环磷酸腺苷的能力。用毒胡萝卜素预处理释放细胞内Ca2 +对基础环磷酸腺苷浓度或VIP诱导的环磷酸腺苷反应没有影响，而与SP + VIP相比，将细胞暴露于SP、毒胡萝卜素和VIP会导致环磷酸腺苷反应降低。SP对VIP反应的增强作用也可被星形孢菌素抑制，但不能被阻断。基于这些结果，可以得出结论，在富含催乳素细胞的培养物中，环磷酸腺苷/PKA和PKC/Ins(1,4,5)P3信使系统之间存在大量的相互作用。关键效应器似乎是PKA、PKCα、β、δ中的一种或多种以及Ins(1,4,5)P3敏感的Ca2 +储存。
