Du X-L, Yang H, Liu S-G, Luo M-L, Hao J-J, Zhang Y, Lin D-C, Xu X, Cai Y, Zhan Q-M, Wang M-R
State Key Laboratory of Molecular Oncology, Cancer Institute (Hospital), Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, China.
Oncogene. 2009 Oct 22;28(42):3714-22. doi: 10.1038/onc.2009.237. Epub 2009 Aug 17.
We have shown earlier that overexpression of Calreticulin (CRT) contributed to a poor prognosis for patients with esophageal squamous cell carcinoma (ESCC). Here, we have shown an important role of CRT in tumorigenesis through enhancing cell motility and anoikis resistance. SiRNA-mediated knockdown of CRT caused impaired cell migration, invasion and resistance to anoikis. Notably, CRT downregulation decreased the expression of Cortactin (CTTN), which has been previously reported as a candidate oncogene associated with anoikis through the PI3K-Akt pathway. In addition, Akt phosphorylation was abolished after CRT downregulation and its activation can be refreshed by CRT upregulation, suggesting that CRT-enhanced cell resistance to anoikis through the CRT-CTTN-PI3K-Akt pathway. Moreover, the CTTN mRNA level was decreased in CRT-siRNA cells, coupled with the inactivation of STAT3. Expression of both CTTN and p-STAT3 was reduced in tumor cells following incubation with the JAK-specific inhibitor, AG490. Chromatin immunoprecipitation assay showed direct binding of p-STAT3 to the conservative STAT3-binding sequences in CTTN promoter. Furthermore, overexpression of CTTN in CRT-downregulated ESCC cells restored its motility and resistance to anoikis. This study not only reveals a role of CRT in motility promotion and anoikis resistance in ESCC cells, but also identifies CRT as an upstream regulator in the CRT-STAT3-CTTN-Akt pathway.
我们之前已经表明，钙网蛋白（CRT）的过表达会导致食管鳞状细胞癌（ESCC）患者预后不良。在此，我们展示了CRT在肿瘤发生过程中通过增强细胞运动性和抗失巢凋亡能力发挥的重要作用。小干扰RNA（SiRNA）介导的CRT敲低导致细胞迁移、侵袭及抗失巢凋亡能力受损。值得注意的是，CRT下调会降低皮层肌动蛋白（CTTN）的表达，此前已有报道称CTTN是通过PI3K-Akt途径与失巢凋亡相关的候选癌基因。此外，CRT下调后Akt磷酸化被消除，而CRT上调可恢复其激活，这表明CRT通过CRT-CTTN-PI3K-Akt途径增强细胞对失巢凋亡的抗性。而且，CRT-siRNA细胞中CTTN mRNA水平降低，同时STAT3失活。用JAK特异性抑制剂AG490处理肿瘤细胞后，CTTN和p-STAT3的表达均降低。染色质免疫沉淀分析表明p-STAT3直接结合CTTN启动子中保守的STAT3结合序列。此外，在CRT下调的ESCC细胞中过表达CTTN可恢复其运动性和抗失巢凋亡能力。本研究不仅揭示了CRT在促进ESCC细胞运动性和抗失巢凋亡方面的作用，还确定了CRT是CRT-STAT3-CTTN-Akt途径中的上游调节因子。
