Cellular Basis Of Action Of Gastrointestinal Peptides/Growth factors

最近的研究表明，在正常和肿瘤组织中，胃肠激素（GI）和GI生长因子（GF）可通过刺激多个细胞内酪氨酸/丝氨酸/苏氨酸磷酸化（TyrP）信号级联以及通过反式激活生长因子受体来引起细胞生长。然而，目前对许多胃肠激素/生长因子激活这些级联的能力知之甚少。在这一年中，我们进行了四项研究，研究各种胃肠激素通过反式激活EGF受体家族来刺激肿瘤生长级联的能力。 在第一项研究中证明，在肺癌细胞中，GI激素神经降压素（NT）刺激这些肿瘤生长的能力依赖于活性氧物质的活化，并且依赖于EGFR和相关EGFR受体HER 2的反式激活。NT刺激EGFR-HER 2异二聚体的形成，其促生长作用被EGFR/HER 2酪氨酸激酶双重抑制剂拉帕替尼阻断。在两项研究中，我们证明了激素垂体腺苷酸环化酶激活肽（PACAP）可以刺激肺癌细胞的生长，并且它通过反式激活EGF受体和HER 3来实现。EGFR反式激活需要磷脂酶C的激活、细胞Ca 2+的动员和活性氧的产生，并且HER 3激活通过与EGFR或HER 2的二聚化发生。在第四项研究中，我们证明在肺癌中蛙皮素通过MAPK依赖性机制以HER 3依赖性方式刺激生长。这些结果显示了新的细胞途径，可能证明可用于抑制这些肿瘤的生长。最近，我们已经证明，p21激活激酶（PAK），这已被广泛研究，其在癌症生长中的作用也是重要的，在正常组织中介导的GI激素/神经递质的一些细胞效应。在过去一年的两项研究中，我们扩展了以前的研究。在一项研究中，我们证明了两种GI激素/神经递质，血管活性肠肽和促胰液素，它们各自与特定的G蛋白偶联受体相互作用以介导它们在分散的胰腺腺泡细胞中的作用，两者都刺激腺泡Na 2+，K2+ ATP酶的激活，该ATP酶介导腺泡电解质/水分泌，并且它依赖于PAK 4机制，其在术语上需要腺苷酸环化酶的激活，随后刺激环AMP依赖性蛋白激酶以及EPAC信号级联的激活。在胰腺腺泡细胞的第二项研究中，我们探讨了PAK 4激活在介导胰腺腺泡细胞的生理激活剂CCK刺激这些细胞中的酶分泌或生长介导级联反应中的作用。我们发现这些细胞中的PAK 4被许多信号级联激活，包括PKC-，Src-，p44/42-和p38-依赖性级联。Pak 4激活所需的酶分泌和激活的MAP激酶，介导这些细胞中的生长级联。这些观察加上最近的研究表明p21激活激酶在胰腺癌生长和胰腺炎等胰腺疾病中也很重要，再加上目前的研究表明其在正常胰腺过程中的重要性，表明它们应该被认为是胰腺细胞中的重要信号分子，并包括在未来的研究中。

Recent studies show that in both normal and neoplastic tissues, gastrointestinal hormones (GI) and GI growth factors (GF) may cause cell growth by stimulating multiple intracellular tyrosine/serine/threonine phosphorylation (TyrP) signaling cascades as well as by transactivation growth factor receptors. However, at present little is known about the ability of many gastrointestinal hormones/growth factors to activate these cascades. During the year we have performed four studies into the ability of various gastrointestinal hormones to stimulate tumoral growth cascades by transactivating the EGF family of receptors. In the first study demonstrated that in lung cancer cells the ability of the GI hormone, neurotensin (NT) to stimulate growth of these tumors was dependent of the activation of reactive oxygen species and was dependent on transactivation of both EGFR and the related EGFR receptor, HER2. NT stimulated the formation of EGFR-HER2 heterodimers and its growth promoting affects were blocked by lapatinib, a dual EGFR/HER2 tyrosine kinase inhibitor. In two studies we demonstrated that the hormone pituitary adenylate cyclase activating peptide(PACAP) can stimulate growth of lung cancer cells and it does so by transactivating the EGF receptor and HER3. The EGFR transactivation requires activation of phospholipase C, mobilization of cellular Ca2+, and generation of reactive oxygen species and HER3 activation occurs via dimerization with EGFR or HER2. In the fourth study we demonstrate in lung cancer the bombesin stimulates growth in a HER3 dependent manner through a MAPK dependent mechanism. These results show novel cellular pathways that may prove useful in inhibitor the growth of these tumors. Recently we have demonstrated at that the p21-activated kinases (PAKs),which have been extensively studied for their roles in cancer growth are also important in mediating some of the cellular effects of GI hormones/neurotransmitters in normal tissues. In two studies over the last year we have extended our previous studies. In one study we demonstrate that the two GI hormones/neurotransmitters, vasoactive intestinal peptide and secretin, which each interact with specify G protein-coupled receptors to mediate their actions in dispersed pancreatic acinar cells, both stimulated activation of acinar Na2+,K2+ ATPase which mediates acinar electrolytes/ water secretion, and that it was dependent on a PAK4 mechanism which in term required activation of adenylate cyclase with subsequent stimulation of cyclic AMP-dependent protein kinase as well as activation of the EPAC signaling cascade. In a second study with pancreatic acinar cells, we explored the role of PAK4 activation in mediating the effects of the physiological activator of pancreatic acinar cells, CCK, to stimulate enzyme secretion or growth mediating cascades in these cells. We found that PAK4 in these cells was activated by numerous signaling cascades including PKC-, Src-, p44/42-, and p38-dependent cascades. Pak4 activation was required for both enzyme secretion and activation of MAP kinases, which mediate growth cascades in these cells. These observations coupled with recent studies showing the p21-activated kinases are also important in such pancreatic diseases as pancreatic cancer growth and pancreatitis, coupled with the present studies showing its importance in normal pancreatic processes, suggest they should be considered an important signaling molecule in pancreatic cells and included in future investigations.