Cellular Basis Of Action Of Gastrointestinal Peptides/Growth factors

最近的研究表明，胃肠道激素/生长因子可能通过刺激多种细胞内酪氨酸磷酸化（TyrP）信号级联反应来刺激细胞生长。然而，目前对许多胃肠道激素/生长因子激活胃肠道组织中这些级联反应的能力知之甚少。我们研究了各种GI激素引起新型丝氨酸/苏氨酸激酶蛋白激酶D（PKD）激活的能力和机制。我们发现只有激活磷脂酶C（PLC）激活PKD1的激素才能引起S916， S744/748的磷酸化，并且激活需要PLC级联的两个肢体。使用显性负PKC，只有PKC δ参与介导这种效应。胃肠道激素CCK通过pkc依赖性机制引起PKD的激活，正如其他组织中的其他刺激物广泛报道的那样，也是通过pkc独立的新型级联。由于存在多个PKC， PKC δ在各种组织中的作用难以确定。抑制剂rotlerin在文献中已被广泛用于此目的。我们在对其在胰腺腺泡中的作用的详细研究中发现，rotlerin引起的抑制并非针对PKC δ的特异性，事实上，各种细胞信号级联的大多数抑制都是由于它作为氧化磷酸化的解偶联剂。因此，该化合物的结果应在每个系统中仔细解释，并确定其特异性。据报道，HGF在胰腺腺泡细胞的生长和损伤恢复中发挥重要作用，并作为重要的生长因子在胰腺癌中发挥作用。我们的研究表明，HGF在GAB1的Y307和Y627 Tyr位点快速有效地刺激GAB1 TyrP。这不仅导致GAB1重新分布到膜上，还刺激了GAB1与许多下游效应物的关联，包括SHP2、PI3K、Shc和Crk亚型，但不包括PLC γ。这种刺激并不依赖于HGF刺激细胞钙变化或激活PKC的能力。这些结果表明，GAB1在HGF而不是其他G蛋白偶联受体改变胰腺腺泡细胞功能的能力中起核心作用。已完成的其他研究包括鉴定人类结肠细胞中调节收缩性的生长抑素受体亚型，以及研究Bombesin受体配体与组蛋白去乙酰化酶抑制剂联合抑制肺癌增殖的能力。

Recent studies show that gastrointestinal hormones/growth factors may stimulate cell growth by stimulating multiple intracellular tyrosine phosphorylation (TyrP) signaling cascades. However at present little is known about the ability of many gastrointestinal hormones/growth factors to activate these cascades in GI tissues. We have investigated the ability and mechanism of various GI hormones to cause activation of the novel serine /threonine kinase protein kinase D(PKD). We found only hormones activating phospholipase C(PLC) activated PKD1 cause phosphorylation of S916, S744/748 and activation required both limbs of the PLC cascade. Using dominant negative PKCs, only PKC delta was involved in mediating this effect. The GI hormone CCK, caused activation OF PKD through both a PKC-dependent mechanism, as is widely reported by other stimulants in other tissues, and also by a novel cascade which was PKC-independent. The role of PKC delta is difficult to define in the various tissues due to the presence of multiple PKCs. The inhibitor rottlerin has been widely used in the literature for this purpose. We found in a detailed study of its action in pancreatic acini the inhibition caused by rottlerin was not specific for PKC delta and in fact most of the inhibition of various cellular signaling cascades was due to it acting as an uncoupler of oxidative phosphorylation. Therefore results with this compound should be carefully interpreted in each system it is used and its specificity established. HGF has been reported to play an important role in growth as well as the recovery from injury of acinar cells as well as function as an important growth factor in pancreatic cancer. Our studies show HGF stimulates GAB1 TyrP rapidly and potently at both the Y307 and Y627 Tyr loci of GAB1. This not only caused a redistribution of GAB1 to the membrane it also stimulated the association of GAB1 with numerous downstream effectors including SHP2, PI3K, Shc and Crk isoforms, but not PLC gamma. This stimulation did not depend on the ability of HGF to stimulate changes in cellular calcium or activate PKC. These results show GAB1 plays a central role in the ability of HGF but not different G protein coupled receptors to alter pancreatic acinar cell function. Additional studies done include the the identification of the somatostatin receptor subtypes meditating contractility in human colonic cells, and studies of the ability of Bombesin receptor ligands in combination with histone deactylase inhibitors to inhibit lung cancer proliferation.