Department of Pathology, Arizona Cancer Center, Tucson, USA.
Cancer Biol Ther. 2010 Nov 15;10(10):1056-66. doi: 10.4161/cbt.10.10.13373.
Prostaglandin E₂ (PGE₂) levels are frequently elevated in colorectal carcinomas. PGE₂ is perceived via four transmembrane G protein coupled receptors (EP1-4), among which the EP4 receptor is most relevant. PGE₂/EP4-receptor interaction activates CREB via the ERK/MEK pathway. However, the downstream target genes activated by this pathway remained to be investigated.
METHODOLOGY/PRINICIPAL FINDINGS: Here, we have identified S100P (an EF-hand calcium binding protein) as a novel downstream target. We show by realtime RT-PCR that S100P mRNA levels are elevated in 14/17 (82%) colon tumor tissues as compared to paired adjacent normal colonic tissues. S100P expression is stimulated in the presence of PGE₂ in a time dependent manner at mRNA and protein levels in colon, breast and pancreatic cancer cells. Pharmacological and RNAi-mediated inhibition of the EP4 receptor attenuates PGE₂-dependent S100P mRNA induction. RNA(i)-mediated knockdown of CREB inhibits endogenous S100P expression. Furthermore, using luciferase reporter analysis and EMSA we show that mutation and/or deletion of the CRE sequence within the S100P promoter abolished PGE₂-mediated transcriptional induction. Finally, we demonstrate that RNA(i)-mediated knockdown of S100P compromised invadopodia formation, colony growth and motility of colon cancer cells. Interestingly, endogenous knock down of S100P decreases ERK expression levels, suggesting a role for ERK in regulating S100P mediated cell growth and motility.
CONCLUSIONS/SIGNIFICANCE: Together, our findings show for the first time that S100P expression is regulated by PGE₂/EP4-receptor signaling and may participate in a feedback signaling that perpetuates tumor cell growth and migration. Therefore, our data suggest that dysregulated S100P expression resulting from aberrant PGE₂/EP4 receptor signaling may have important consequences relevant to colon cancer pathogenesis.
前列腺素 E₂（PGE₂）水平在结直肠癌中经常升高。PGE₂ 通过四个跨膜 G 蛋白偶联受体（EP1-4）被感知，其中 EP4 受体最为相关。PGE₂/EP4 受体相互作用通过 ERK/MEK 途径激活 CREB。然而，该途径激活的下游靶基因仍有待研究。
方法/主要发现：在这里，我们将 S100P（一种 EF 手钙结合蛋白）鉴定为一种新的下游靶标。我们通过实时 RT-PCR 显示，与配对的相邻正常结肠组织相比，14/17（82%）结肠肿瘤组织中的 S100P mRNA 水平升高。在存在 PGE₂ 的情况下，S100P 在 mRNA 和蛋白质水平上以时间依赖性方式在结肠、乳腺和胰腺癌细胞中受到刺激。EP4 受体的药理学和 RNAi 抑制可减弱 PGE₂ 依赖性 S100P mRNA 诱导。CREB 的 RNAi 抑制可抑制内源性 S100P 表达。此外，我们使用荧光素酶报告分析和 EMSA 表明，S100P 启动子内 CRE 序列的突变和/或缺失消除了 PGE₂ 介导的转录诱导。最后，我们证明了 S100P 的 RNAi 介导敲低会损害结肠癌细胞的侵袭伪足形成、集落生长和运动性。有趣的是，内源性 S100P 敲低会降低 ERK 表达水平，表明 ERK 在调节 S100P 介导的细胞生长和运动性中起作用。
结论/意义：总之，我们的研究结果首次表明，S100P 的表达受 PGE₂/EP4 受体信号调节，并且可能参与促进肿瘤细胞生长和迁移的反馈信号。因此，我们的数据表明，由于异常的 PGE₂/EP4 受体信号导致的 S100P 表达失调可能对结肠癌的发病机制具有重要意义。
