Volakaki Aspasia-Athina, Lafkas Daniel, Kassi Eva, Schally Andrew V, Papavassiliou Athanasios G, Kiaris Hippokratis
Department of Biological Chemistry, University of Athens Medical School, 11527 Athens, Greece.
J Mol Endocrinol. 2008 Nov;41(5):389-92. doi: 10.1677/JME-08-0106. Epub 2008 Sep 2.
GHRH, besides its neuroendocrine action in controlling the release of GH from the pituitary, stimulates the growth of various cancers in vivo and in vitro by direct mechanism(s). However, the molecular mechanism that mediates these proliferative effects of GHRH in extrapituitary tissues remains poorly characterized. In the present study, we investigated whether the tumor suppressor p21/waf1 is involved in the mediation of the proliferative effects of GHRH in A549 human lung cancer epithelial cells. Exposure of A549 cells to the GHRH antagonist JMR-132 caused a significant inhibition in the rate of cell proliferation. In A549 cells, GHRH suppressed while JMR-132 increased the levels of p21 expression in a dose-dependent manner. This suggests that GHRH could regulate p21 levels. We then evaluated whether p21 is required in A549 cells for the regulation of cell proliferation by GHRH. To this end, we knocked-down p21 expression in A549 cells by siRNA and assessed the effects of antagonist JMR-132 on cell proliferation. We found that the loss of p21 expression abolished the anti-proliferative effects of JMR-132. Suppression of p21 expression by siRNA in human HT29 colon cancer cells and non-transformed mouse osteoblasts KS483 also blocked the anti-proliferative effects of JMR-132 suggesting that the regulation of cell proliferation by GHRH is p21 dependent. These results shed light on the molecular mechanism of action of GHRH antagonists in tumor tissues and suggest that the antineoplastic activity of GHRH antagonists could be considered for the treatment of cancers expressing p21.
生长激素释放激素（GHRH）除了在控制垂体生长激素释放方面具有神经内分泌作用外，还通过直接机制在体内和体外刺激多种癌症的生长。然而，介导GHRH在垂体外组织中这些增殖作用的分子机制仍不清楚。在本研究中，我们调查了肿瘤抑制因子p21/waf1是否参与介导GHRH在A549人肺癌上皮细胞中的增殖作用。将A549细胞暴露于GHRH拮抗剂JMR-132会导致细胞增殖速率显著抑制。在A549细胞中，GHRH以剂量依赖性方式抑制而JMR-132增加p21表达水平。这表明GHRH可以调节p21水平。然后我们评估了在A549细胞中p21对于GHRH调节细胞增殖是否是必需的。为此，我们通过小干扰RNA（siRNA）敲低A549细胞中的p21表达，并评估拮抗剂JMR-132对细胞增殖的影响。我们发现p21表达缺失消除了JMR-132的抗增殖作用。在人HT29结肠癌细胞和未转化的小鼠成骨细胞KS483中，通过siRNA抑制p21表达也阻断了JMR-132的抗增殖作用，这表明GHRH对细胞增殖的调节是p21依赖性的。这些结果揭示了GHRH拮抗剂在肿瘤组织中的分子作用机制，并表明GHRH拮抗剂的抗肿瘤活性可考虑用于治疗表达p21的癌症。
