Abstract 2901: Pdcd4 inhibits slug translation to suppress E-cadherin expression and invasion in colon tumor cells

Abstract

Abstract Programmed cell death 4 (Pdcd4) has been demonstrated to function as a tumor suppressor and protein translation inhibitor. We previously reported that knockdown of Pdcd4 down-regulated E-cadherin expression. E-cadherin is a key regulator for tumor cell invasion and metastasis, whose expression is controlled by transcription repressors Snail, Slug, ZEB1/2, and Twist. Both Slug and Snail have been shown to repress E-cadherin expression and contribute to tumor progression in various cancers including colon cancer. Here, we reported that knockdown of Pdcd4 increased Slug protein level but not SLUG mRNA level in colon tumor cells. Conversely, over-expression of Pdcd4 decreased Slug expression. Using sucrose gradient fractionation assays, Pdcd4 knockdown was found to increase the population of SLUG mRNA in the polysomal fractions. These results indicate that Pdcd4 translationally regulates Slug expression. To understand the mechanism by which Pdcd4 regulates Slug translation, the SLUG 5' untranslated region (5'UTR) was cloned and fused with luciferase reporter and named as 5'UTR-Slug-Luc. Knockdown of Pdcd4 significantly enhanced the translation of 5'UTR-Slug-Luc while ectopic expression of Pdcd4 repressed the translation of 5'UTR-Slug-Luc, suggesting that SLUG 5'UTR is an essential element for Pdcd4 to inhibit Slug translation. Moreover, cells treated with silvestrol, an inhibitor for translation initiation factor 4A (eIF4A), significantly suppressed Slug translation. In addition, ectopic expression of Pdcd4 inhibited Slug translation and thereby decreased E-cadherin expression. By contrast, Pdcd4(D418A), a mutant that does not bind with eIF4A, failed to suppress the expression of Slug and E-cadherin. These findings suggest that Pdcd4-inhibited Slug translation is through suppressing eIF4A. Furthermore, knockdown of Slug in Pdcd4 knockdown cells restored the E-cadherin expression and reversed the invasive capacity induced by Pdcd4 knockdown, indicating that up-regulation of Slug contributes to Pdcd4-knockdown enhanced invasion. Taken together, this study demonstrates that Pdcd4 inhibits translation of Slug to regulate E-cadherin expression and invasion in colon tumor cells. Citation Format: Qing Wang, Jiang Zhu, Hsin-Sheng Yang. Pdcd4 inhibits slug translation to suppress E-cadherin expression and invasion in colon tumor cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2901.