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Updated: Feb 27, 2026
Assessment of Selective mRNA Translation in Mammalian Cells by Polysome Profiling
Published on: October 28, 2014
Tumor suppressor Pdcd4 attenuates Sin1 translation to inhibit invasion in colon carcinoma
1Department of Toxicology and Cancer Biology, College of Medicine, University of Kentucky, Lexington, KY, USA.
Abstract:
Programmed cell death 4 (Pdcd4), a tumor invasion suppressor, is frequently downregulated in colorectal cancer and other cancers. In this study, we find that loss of Pdcd4 increases the activity of mammalian target of rapamycin complex 2 (mTORC2) and thereby upregulates Snail expression. Examining the components of mTORC2 showed that Pdcd4 knockdown increased the protein but not mRNA level of stress-activated-protein kinase interacting protein 1 (Sin1), which resulted from enhanced Sin1 translation. To understand how Pdcd4 regulates Sin1 translation, the SIN1 5' untranslated region (5'UTR) was fused with luciferase reporter and named as 5'Sin1-Luc. Pdcd4 knockdown/knockout significantly increased the translation of 5'Sin1-Luc but not the control luciferase without the SIN1 5'UTR, suggesting that Sin1 5'UTR is necessary for Pdcd4 to inhibit Sin1 translation. Ectopic expression of wild-type Pdcd4 and Pdcd4(157-469), a deletion mutant that binds to translation initiation factor 4A (eIF4A), sufficiently inhibited Sin1 translation, and thus suppressed mTORC2 kinase activity and invasion in colon tumor cells. By contrast, Pdcd4(157-469)(D253A,D418A), a mutant that does not bind to eIF4A, failed to inhibit Sin1 translation, and consequently failed to repress mTORC2 activity and invasion. In addition, directly inhibiting eIF4A with silvestrol significantly suppressed Sin1 translation and attenuated invasion. These results indicate that Pdcd4-inhibited Sin1 translation is through suppressing eIF4A, and functionally important for suppression of mTORC2 activity and invasion. Moreover, in colorectal cancer tissues, the Sin1 protein but not mRNA was significantly upregulated while Pdcd4 protein was downregulated, suggesting that loss of Pdcd4 might correlate with Sin1 protein level but not mRNA level in colorectal cancer patients. Taken together, our work reveals a novel mechanism by which Pdcd4 inhibits Sin1 translation to attenuatemTORC2 activity and thereby suppresses invasion.
Insights
Programmed cell death 4 (Pdcd4) suppresses tumor invasion by inhibiting stress-activated-protein kinase interacting protein 1 (Sin1) translation via eIF4A. Loss of Pdcd4 upregulates Sin1, increasing mTORC2 activity and cancer cell invasion.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Signaling
Background:
- Programmed cell death 4 (Pdcd4) is a tumor suppressor frequently downregulated in colorectal cancer.
- Loss of Pdcd4 is linked to increased tumor invasion and progression.
- The precise mechanisms by which Pdcd4 exerts its tumor-suppressive functions are not fully elucidated.
Purpose of the Study:
- To investigate the role of Pdcd4 in regulating mammalian target of rapamycin complex 2 (mTORC2) activity and its downstream effect on tumor invasion.
- To identify the molecular targets and mechanisms through which Pdcd4 inhibits cancer cell invasion.
- To explore the correlation between Pdcd4 and Sin1 expression in colorectal cancer tissues.
Main Methods:
- Utilized cell culture models with Pdcd4 knockdown and knockout.
- Employed luciferase reporter assays to assess Sin1 translation.
- Investigated protein and mRNA levels of key signaling molecules including Sin1 and mTORC2 components.
- Used site-directed mutagenesis to study the interaction of Pdcd4 with translation initiation factor 4A (eIF4A).
- Administered silvestrol, an eIF4A inhibitor, to evaluate its effect on Sin1 translation and invasion.
Main Results:
- Pdcd4 deficiency led to increased mTORC2 activity and Snail expression.
- Pdcd4 knockdown enhanced the translation of stress-activated-protein kinase interacting protein 1 (Sin1) via its 5' untranslated region (5'UTR).
- Pdcd4 directly binds to eIF4A, inhibiting Sin1 translation and subsequently suppressing mTORC2 activity and colon tumor cell invasion.
- In colorectal cancer tissues, Pdcd4 protein was downregulated, while Sin1 protein was upregulated, suggesting a clinical correlation.
Conclusions:
- Pdcd4 suppresses tumor invasion by inhibiting Sin1 translation through its interaction with eIF4A.
- This mechanism is crucial for attenuating mTORC2 activity and preventing cancer cell invasion.
- The findings reveal a novel pathway involving Pdcd4, Sin1 translation, and mTORC2 signaling in colorectal cancer pathogenesis.
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