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，胃肠道激素（GI）和胃肠道生长因子（GF）可能通过刺激细胞内多种酪氨酸/丝氨酸/苏氨酸磷酸化（TyrP）信号级联以及通过反激活生长因子受体来促进细胞生长。然而，目前对许多胃肠道激素/生长因子激活这些级联反应的能力知之甚少。在这一年中，我们进行了四项研究，研究各种胃肠道激素通过激活EGF受体家族来刺激肿瘤级联生长的能力。第一项研究表明，在肺癌细胞中，GI激素，神经紧张素（NT）刺激这些肿瘤生长的能力依赖于活性氧的激活，并依赖于EGFR和相关EGFR受体HER2的反激活。NT刺激EGFR-HER2异源二聚体的形成，其促进生长的作用被双重EGFR/HER2酪氨酸激酶抑制剂拉帕替尼阻断。在两项研究中，我们证明垂体腺苷酸环化酶激活肽（PACAP）激素可以通过反激活EGF受体和HER3来刺激肺癌细胞的生长。EGFR的反式激活需要磷脂酶C的激活、细胞Ca2+的动员和活性氧的产生，HER3的激活通过与EGFR或HER2的二聚化发生。在第四项研究中，我们证明了在肺癌中，bombesin通过MAPK依赖机制以HER3依赖的方式刺激生长。这些结果显示了新的细胞途径，可能被证明对抑制这些肿瘤的生长有用。最近，我们已经证明，p21活化激酶（PAKs）在癌症生长中的作用已被广泛研究，在正常组织中介导GI激素/神经递质的一些细胞效应也很重要。在去年的两项研究中，我们扩展了之前的研究。在一项研究中，我们证明了两种GI激素/神经递质，血管活性肠肽和分泌素，它们各自与特定的G蛋白偶联受体相互作用，介导它们在分散的胰腺腺泡细胞中的作用，它们都刺激了介导腺泡电解质/水分泌的腺泡Na2+，K2+ atp酶的激活。它依赖于PAK4机制，这就需要激活腺苷酸环化酶，随后刺激环amp依赖性蛋白激酶，以及激活EPAC信号级联。在第二项针对胰腺腺泡细胞的研究中，我们探索了PAK4激活在介导胰腺腺泡细胞生理激活剂CCK的作用中的作用，以刺激这些细胞中的酶分泌或生长介导级联反应。我们发现这些细胞中的PAK4被许多信号级联激活，包括PKC-， Src-， p44/42-和p38依赖性级联。Pak4激活是酶分泌和MAP激酶激活所必需的，MAP激酶介导这些细胞的生长级联反应。这些观察结果加上最近的研究表明p21活化激酶在胰腺癌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，表明它们应被视为胰腺细胞中重要的信号分子，并纳入未来的研究。

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.