Leone Vincenza, di Palma Antonella, Ricchi Paolo, Acquaviva Fabio, Giannouli Maria, Di Prisco Anna Maria, Iuliano Francesca, Acquaviva Angela M
Dipartimento di Biologia e Patologia Cellulare e Molecolare L. Califano, Università degli Studi di Napoli Federico II, Via Pansini, 5, 80131, Napoli, Italy.
Am J Physiol Gastrointest Liver Physiol. 2007 Oct;293(4):G673-81. doi: 10.1152/ajpgi.00584.2006. Epub 2007 Jul 19.
PGE2 plays a critical role in colorectal carcinogenesis. We have previously shown that COX-2 expression and PGE2 synthesis are mediated by IGF-II/IGF-I receptor signaling in the Caco-2 cell line and that the pathway of phosphatidylinositol 3-kinase (PI3K)/Akt protects the cell from apoptosis. In the present study, we demonstrate that PGE2 has the ability to increase Ras and PI3K association and decrease the level of apoptosis in the same experimental system. The effect of PGE2 on PI3K/Ras association is dependent on the activation of EP4 receptor, the increase of cAMP levels, and the activation of PKA. In fact, treatment of cells with the PKA inhibitor H89 decreases the association of Ras and PI3K and Ras-associated PI3K activity. PKA inhibitor H89 is able to decrease threonine phosphorylation of Akt and to increase serine phosphorylation of Akt by p38 MAPK and counteracts the cytoprotective effect induced by PGE2. In addition, PGE2 is able to activate p38 MAPK and the inhibition of p38 MAPK, with SB203580 specific inhibitor or with dominant negative MKK6 kinase, is able to revert the apoptotic effect of H89 and serine phosphorylation of Akt. The effect of PGE2 on Caco-2 cell survival through PKA activation is mediated and regulated by the balance of threonine/serine phosphorylation of Akt by p38 kinase and PI3K. In conclusion, our data elucidate a novel mechanism for regulation of colon cancer cell survival and provide evidences for new combinatory treatments of colon cancer.
前列腺素E2（PGE2）在结直肠癌发生过程中起关键作用。我们之前已经表明，在Caco-2细胞系中，环氧合酶-2（COX-2）的表达和PGE2的合成是由胰岛素样生长因子-II/胰岛素样生长因子-I受体信号介导的，并且磷脂酰肌醇3-激酶（PI3K）/蛋白激酶B（Akt）通路可保护细胞免于凋亡。在本研究中，我们证明在同一实验系统中，PGE2有能力增加Ras与PI3K的结合并降低凋亡水平。PGE2对PI3K/Ras结合的作用取决于EP4受体的激活、环磷酸腺苷（cAMP）水平的升高以及蛋白激酶A（PKA）的激活。事实上，用PKA抑制剂H89处理细胞会降低Ras与PI3K的结合以及Ras相关的PI3K活性。PKA抑制剂H89能够降低Akt的苏氨酸磷酸化水平，并通过p38丝裂原活化蛋白激酶（MAPK）增加Akt的丝氨酸磷酸化水平，从而抵消PGE2诱导的细胞保护作用。此外，PGE2能够激活p38 MAPK，用SB203580特异性抑制剂或显性负性MKK6激酶抑制p38 MAPK，能够逆转H89的凋亡作用以及Akt的丝氨酸磷酸化。PGE2通过PKA激活对Caco-2细胞存活的影响是由p38激酶和PI3K对Akt的苏氨酸/丝氨酸磷酸化平衡介导和调节的。总之，我们的数据阐明了一种调节结肠癌细胞存活的新机制，并为结肠癌的新联合治疗提供了证据。
