An evolutionarily conserved interaction of tumor suppressor protein Pdcd4 with the poly(A)-binding protein contributes to translation suppression by Pdcd4

miR-21-5p inhibits inflammation injuries in LPS-treated H9c2 cells by regulating PDCD4

OBJECTIVES

To explore the expression levels and the potential regulatory mechanism of miR-21-5p in LPS-treated H9c2 cells.

METHODS

The secretions of the inflammatory cytokines induced by LPS in H9c2 cells were evaluated using ELISA. We used RT-RCR and western blot to measure the relative mRNA and protein expression levels in LPS-treated H9c2 cells. CCK-8 and EdU assays showed the viability and proliferation profiles of the H9c2 cells. TUNEL assays demonstrated the apoptotic behaviors of the H9c2 cells, and a luciferase reporter analysis was used to investigate the interactions between miR-21-5p and programmed cell death protein 4 (PDCD4).

RESULTS

LPS induced damage to the H9c2 cells by reducing the cell viability and down-regulating miR-21-5p. On the other hand, miR-21-5p overexpression inhibited the LPS-induced inflammatory damage in the H9c2 cells. Moreover, PDCD4 was verified as a downstream target gene of miR-21-5p, and its expression was inhibited by the higher miR-21-5p content. Finally, miR-21-5p inhibited septic processes, and the PDCD4 overexpression rescued the miR-21-5p effect in the LPS-treated H9c2 cells.

CONCLUSION

Our findings suggest that miR-21-5p inhibits the LPS-induced progression of sepsis in H9c2 cells. Additionally, PDCD4 is a downstream target gene of miR-21-5p, and both molecules serve as potential therapeutic targets for heart sepsis patients.

Discovery of a novel role of tumor suppressor PDCD4 in stimulation of translation termination

Programmed cell death 4 protein (PDCD4) regulates many vital cell processes, although is classified as a tumor suppressor because it inhibits neoplastic transformation and tumor growth. For example, PCDC4 has been implicated in the regulation of transcription and mRNA translation. PDCD4 is known to inhibit translation initiation by binding to eukaryotic initiation factor 4A and elongation of oncogenic c- and A-myb mRNAs. Additionally, PDCD4 has been shown to interact with poly(A)-binding protein (PABP), which affects translation termination, although the significance of this interaction is not fully understood. Considering the interaction between PABP and PDCD4, we hypothesized that PDCD4 may also be involved in translation termination. Using in vitro translation systems, we revealed that PDCD4 directly activates translation termination. PDCD4 stimulates peptidyl-tRNA hydrolysis induced by a complex of eukaryotic release factors, eRF1-eRF3. Moreover, in combination with the PABP, which also stimulates peptide release, PDCD4 activity in translation termination increases. PDCD4 regulates translation termination by facilitating the binding of release factors to the ribosome, increasing the GTPase activity of eRF3, and dissociating eRF3 from the posttermination complex. Using a toe-printing assay, we determined the first stage at which PDCD4 functions-binding of release factors to the A-site of the ribosome. However, preventing binding of eRF3 with PABP, PDCD4 suppresses subsequent rounds of translation termination. Based on these data, we assumed that human PDCD4 controls protein synthesis during translation termination. The described mechanism of the activity of PDCD4 in translation termination provides a new insight into its functioning during suppression of protein biosynthesis.

Long non-coding RNA LINC01018 inhibits the progression of acute myeloid leukemia by targeting miR-499a-5p to regulate PDCD4

Acute myeloid leukemia (AML) is a highly heterogeneous disease with a very high mortality rate. In recent years, an increasing number of studies have proven that long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) may serve as useful biomarkers in various cancer types. However, the mechanism of LINC01018 and miR-499a-5p in AML requires further investigation. The mRNA expression of LINC01018, miR-499a-5p and PDCD4 in AML tissues and cells was detected using reverse transcription-quantitative polymerase chain reaction. Cell proliferation was measured using Cell Counting kit-8 and EdU assays. Cell apoptosis was monitored via a TUNEL staining assay. Protein expression of PDCD4, Bax and Bcl-2 was measured using western blot analysis. The interaction between PDCD4 and LINC01018 or miR-499a-5p was verified by RNA pull-down, RIP and dual-luciferase reporter assays. LINC01018 and PDCD4 were downregulated in AML, while miR-499a-5p was upregulated. LINC01018-overexpression suppressed AML cell proliferation and induced AML cell apoptosis, while miR-499a-5p transfection reversed these effects. LINC01018 acted as a sponge of miR-499a-5p, and PDCD4 was demonstrated to be targeted by miR-499a-5p. Knockdown of miR-499a-5p suppressed AML cell proliferation and promoted AML cell apoptosis, but silencing PDCD4 abolished this effect. LINC01018 inhibited AML cell growth by modulating PDCD4 through suppression of miR-499a-5p, providing a feasible theoretical basis for the treatment of AML.

WD Repeat Domain 77 Protein Regulates Translation of E2F1 and E2F3 mRNA

WD repeat domain 77 protein (WDR77) is required for cellular proliferation of lung and prostate epithelial cells during earlier stages of development and is reactivated during prostate and lung tumorigenesis. WDR77 plays an essential role in prostate tumorigenesis and cell growth mediated by growth regulatory factors. Here, we identified E2F1 and E2F3 mRNAs as translational targets of WDR77. We demonstrated that WDR77 regulated the translation of E2F1 and E2F3 mRNAs through the 5' untranslated regions (UTRs) of E2F1 and E2F3 (E2F1/3) mRNAs. WDR77 physically interacted with programmed cell death 4 (PDCD4) that suppresses translation of mRNAs containing structured 5' UTRs by interacting with eukaryotic translation initiation factor 4A (eIF4A) and inhibiting its helicase activity. Further, we demonstrated that the interaction between WDR77 and PDCD4 prevented the binding of PDCD4 to eIF4A and relieved PDCD4's inhibitory effect on eIF4A1. Overall, our work reveals for the first time that WDR77 is directly involved in translational regulation of E2F1/3 mRNAs through their structured 5' UTRs, PDCD4, and eIF4A1 and provides novel insight into the cell growth controlled by WDR77.

Programmed cell death factor 4 (PDCD4), a novel therapy target for metabolic diseases besides cancer

Programmed cell death factor 4 (PDCD4) is originally described as a tumor suppressor gene that exerts antineoplastic effects by promoting apoptosis and inhibiting tumor cell proliferation, invasion, and metastasis. Several investigations have probed the aberrant expression of PDCD4 with the progression of metabolic diseases, such as polycystic ovary syndrome (PCOS), obesity, diabetes, and atherosclerosis. It has been ascertained that PDCD4 causes glucose and lipid metabolism disorders, insulin resistance, oxidative stress, chronic inflammatory response, and gut flora disorders to regulate the progression of metabolic diseases. This review aims to summarize the latest researches to uncover the structure, expression regulation, and biological functions of PDCD4 and to elucidate the regulatory mechanism of the development of tumors and metabolic diseases. This review has emphasized the understanding of the PDCD4 role and to provide new ideas for the research, diagnosis, and treatment of tumors and metabolic diseases.

Programmed cell death 4 modulates lysosomal function by inhibiting TFEB translation

Transcription factor EB (TFEB) is a master regulator of autophagy and lysosomal biogenesis. The post-translational phosphorylation modulations of TFEB by mTOR and ERK signaling can determine its nucleocytoplasmic shuttling and activity in response to nutrient availability. However, regulations of TFEB at translational level are rarely known. Here, we found that programmed cell death 4 (PDCD4), a tumor suppressor, decreased levels of nuclear TFEB to inhibit lysosome biogenesis and function. Mechanistically, PDCD4 reduces global pool of TFEB by suppressing TFEB translation in an eIF4A-dependent manner, rather than influencing mTOR- and ERK2-dependnet TFEB nucleocytoplasmic shuttling. Both of MA3 domains within PDCD4 are required for TFEB translation inhibition. Furthermore, TFEB is required for PDCD4-mediated lysosomal function suppression. In the tumor microenvironment, PDCD4 deficiency promotes the anti-tumor effect of macrophage via enhancing TFEB expression. Our research reveals a novel PDCD4-dependent TFEB translational regulation and supports PDCD4 as a potential therapeutic target for lysosome dysfunction related diseases.

PDCD4 controls the G1/S-phase transition in a telomerase-immortalized epithelial cell line and affects the expression level and translation of multiple mRNAs

PDCD4, the protein encoded by the tumor suppressor gene PDCD4 (programmed cell death 4) has been implicated in the control of cellular transcription and translation by modulating the activity of specific transcription factors and suppressing the translation of mRNAs with structured 5′-UTRs. Most studies of human PDCD4 have employed tumor cell lines, possibly resulting in a biased picture of its role in normal cells. Here, we have studied the function of PDCD4 in a telomerase-immortalized human epithelial cell line. We show for the first time that PDCD4 is required for the G1/S-transition, demonstrating its crucial role in the cell cycle. Inhibition of p53-dependent activation of p21^WAF1/CIP1 overrides the requirement for PDCD4 for the G1/S-transition, suggesting that PDCD4 counteracts basal p53 activity to prevent activation of the G1/S checkpoint by p53. Transcriptome and ribosome profiling data show that silencing of PDCD4 changes the expression levels and translation of many mRNAs, providing an unbiased view of the cellular processes that are affected by PDCD4 in an epithelial cell line. Our data identify PDCD4 as a key regulator of cell cycle- and DNA-related functions that are inhibited when it is silenced, suggesting that decreased expression of PDCD4 might contribute to tumor development by compromising genomic integrity.

Control Mechanisms of the Tumor Suppressor PDCD4: Expression and Functions

PDCD4 is a novel tumor suppressor to show multi-functions inhibiting cell growth, tumor invasion, metastasis, and inducing apoptosis. PDCD4 protein binds to the translation initiation factor eIF4A, some transcription factors, and many other factors and modulates the function of the binding partners. PDCD4 downregulation stimulates and PDCD4 upregulation inhibits the TPA-induced transformation of cells. However, PDCD4 gene mutations have not been found in tumor cells but gene expression was post transcriptionally downregulated by micro environmental factors such as growth factors and interleukins. In this review, we focus on the suppression mechanisms of PDCD4 protein that is induced by the tumor promotors EGF and TPA, and in the inflammatory conditions. PDCD4-protein is phosphorylated at 2 serines in the SCF^βTRCP ubiquitin ligase binding sequences via EGF and/or TPA induced signaling pathway, ubiquitinated, by the ubiquitin ligase and degraded in the proteasome system. The PDCD4 protein synthesis is inhibited by microRNAs including miR21.

Expression of tumor suppressor programmed cell death 4 in endometrioid endometrial carcinomas and clinicopathological significance

Programmed cell death 4 (PDCD4), as a novel tumor suppressor, serves important roles in the pathogenesis of tumors. The expression of PDCD4 is downregulated or lost in various human tumors. However, the expression of PDCD4 in endometrial cancer and the clinicopathological significance remain unclear. The aim of the present study was to investigate the expression of PDCD4 in endometrioid endometrial carcinoma (EEC) and the association with clinicopathological parameters. The expression of PDCD4 in EEC tissues and control endometrium was detected by reverse transcription-quantitative polymerase chain reaction, western blotting and immunohistochemistry. PDCD4 expression was also investigated in control endometrial glandular epithelial cells and the endometrial cancer KLE cell line by immunocytochemistry, and the association between PDCD4 expression and clinicopathological parameters of patients with EEC was analyzed. The results demonstrated that PDCD4-positive staining was mainly located in the cytoplasm of endometrial glandular epithelial cells and EEC cells. The staining index of PDCD4 in the proliferative phase was significantly increased compared with that in the secretory phase of control endometrium (P<0.001). There was significantly decreased PDCD4 expression in grade (G) 2/3 EEC tissues compared with the proliferative phase of control endometrium (P<0.001). PDCD4 expression was significantly associated with tumor grade. The PDCD4 levels in G1 EEC tissues were higher compared with the G2/3 EEC group (P<0.01). The results indicated that PDCD4 is associated with the histological grade of EEC, and that PDCD4 may be a valuable indicator of the degree of tumor malignancy in patients with EEC.

The role of Pdcd4 in tumour suppression and protein translation

Programmed cell death 4 (Pdcd4), a tumour suppressor, is frequently down-regulated in various types of cancer. Pdcd4 has been demonstrated to efficiently suppress tumour promotion, progression and proliferation. The biochemical function of Pdcd4 is a protein translation inhibitor. Although the fact that Pdcd4 inhibits protein translation has been known for more than a decade, the mechanism by which Pdcd4 controls tumorigenesis through translational regulation of its target genes is still not fully understood. Recent studies show that Pdcd4 inhibits translation of stress-activated-protein kinase interacting protein 1 to suppress tumour invasion, depicting a picture of how Pdcd4 inhibits tumorigenesis through translational inhibition. Thus, understanding the mechanism of how Pdcd4 attenuates tumorigenesis by translational control should provide a new strategy for combating cancer.

MRF Family Genes Are Involved in Translation Control, Especially under Energy-Deficient Conditions, and Their Expression and Functions Are Modulated by the TOR Signaling Pathway

Dynamic control of protein translation in response to the environment is essential for the survival of plant cells. Target of rapamycin (TOR) coordinates protein synthesis with cellular energy/nutrient availability through transcriptional modulation and phosphorylation of the translation machinery. However, mechanisms of TOR-mediated translation control are poorly understood in plants. Here, we report that Arabidopsis thaliana MRF (MA3 DOMAIN-CONTAINING TRANSLATION REGULATORY FACTOR) family genes encode translation regulatory factors under TOR control, and their functions are particularly important in energy-deficient conditions. Four MRF family genes (MRF1-MRF4) are transcriptionally induced by dark and starvation (DS). Silencing of multiple MRFs increases susceptibility to DS and treatment with a TOR inhibitor, while MRF1 overexpression decreases susceptibility. MRF proteins interact with eIF4A and cofractionate with ribosomes. MRF silencing decreases translation activity, while MRF1 overexpression increases it, accompanied by altered ribosome patterns, particularly in DS. Furthermore, MRF deficiency in DS causes altered distribution of mRNAs in sucrose gradient fractions and accelerates rRNA degradation. MRF1 is phosphorylated in vivo and phosphorylated by S6 kinases in vitro. MRF expression and MRF1 ribosome association and phosphorylation are modulated by cellular energy status and TOR activity. We discuss possible mechanisms of the function of MRF family proteins under normal and energy-deficient conditions and their functional link with the TOR pathway.

Tumor suppressor Pdcd4 attenuates Sin1 translation to inhibit invasion in colon carcinoma

Programmed cell death 4 (Pdcd4), a tumor invasion suppressor, is frequently down-regulated 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 up-regulated while Pdcd4 protein was down-regulated, 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.

Role of Eukaryotic Initiation Factors during Cellular Stress and Cancer Progression

Protein synthesis can be segmented into distinct phases comprising mRNA translation initiation, elongation, and termination. Translation initiation is a highly regulated and rate-limiting step of protein synthesis that requires more than 12 eukaryotic initiation factors (eIFs). Extensive evidence shows that the transcriptome and corresponding proteome do not invariably correlate with each other in a variety of contexts. In particular, translation of mRNAs specific to angiogenesis, tumor development, and apoptosis is altered during physiological and pathophysiological stress conditions. In cancer cells, the expression and functions of eIFs are hampered, resulting in the inhibition of global translation and enhancement of translation of subsets of mRNAs by alternative mechanisms. A precise understanding of mechanisms involving eukaryotic initiation factors leading to differential protein expression can help us to design better strategies to diagnose and treat cancer. The high spatial and temporal resolution of translation control can have an immediate effect on the microenvironment of the cell in comparison with changes in transcription. The dysregulation of mRNA translation mechanisms is increasingly being exploited as a target to treat cancer. In this review, we will focus on this context by describing both canonical and noncanonical roles of eIFs, which alter mRNA translation.

eIF4A RNA Helicase Associates with Cyclin-Dependent Protein Kinase A in Proliferating Cells and Is Modulated by Phosphorylation

Eukaryotic initiation factor 4A (eIF4A) is a highly conserved RNA-stimulated ATPase and helicase involved in the initiation of messenger RNA translation. Previously, we found that eIF4A interacts with cyclin-dependent kinase A (CDKA), the plant ortholog of mammalian CDK1. Here, we show that this interaction occurs only in proliferating cells where the two proteins coassociate with 5'-cap-binding protein complexes, eIF4F or the plant-specific eIFiso4F. CDKA phosphorylates eIF4A on a conserved threonine residue (threonine-164) within the RNA-binding motif 1b TPGR. In vivo, a phospho-null (APGR) variant of the Arabidopsis (Arabidopsis thaliana) eIF4A1 protein retains the ability to functionally complement a mutant (eif4a1) plant line lacking eIF4A1, whereas a phosphomimetic (EPGR) variant fails to complement. The phospho-null variant (APGR) rescues the slow growth rate of roots and rosettes, together with the ovule-abortion and late-flowering phenotypes. In vitro, wild-type recombinant eIF4A1 and its phospho-null variant both support translation in cell-free wheat germ extracts dependent upon eIF4A, but the phosphomimetic variant does not support translation and also was deficient in ATP hydrolysis and helicase activity. These observations suggest a mechanism whereby CDK phosphorylation has the potential to down-regulate eIF4A activity and thereby affect translation.

Down-regulation of tumor suppressor PDCD4 expression in endometrium of adenomyosis patients

OBJECTIVE

Adenomyosis is a common benign gynecological disease which has some malignant behaviors. Programmed cell death 4 (PDCD4) is a newly identified tumor suppressor gene which lowly expresses in various cancers. However, the expression status of PDCD4 in endometrium of adenomyosis patients has not been investigated. The aim of this study is to assess the expression levels of PDCD4 in endometrium of normal controls and adenomyosis patients.

METHODS

The expression of PDCD4 in endometrium of normal controls and eutopic or ectopic endometrium of patients with adenomyosis was evaluated with quantitative real-time PCR, western blot and immunohistochemistry. In addition, the levels of serum estradiol and progesterone in normal controls and adenomyosis patients were detected using electrochemiluminescence immunoassay.

RESULTS

The results showed that PDCD4 mainly expressed in the cytoplasma of glandular epithelium of control endometrium and varied during the cycle changes of endometrium, which may be regulated by changing concentrations of progesterone in the menstrual cycle. Compared with the proliferative phase of control endometrium, PDCD4 expression was down-regulated in proliferative phase of eutopic endometrium or ectopic endometrium, and there was no cyclic variation of PDCD4 expression in eutopic endometrium of adenomyosis patients due to progesterone resistance.

CONCLUSION

These results suggest that PDCD4 may be involved in the pathogenesis of adenomyosis, which will provide a novel strategy for the early diagnosis and new therapeutic target of adenomyosis.

PDCD4 Deficiency Aggravated Colitis and Colitis-associated Colorectal Cancer Via Promoting IL-6/STAT3 Pathway in Mice

BACKGROUND

Although programmed cell death (PDCD) 4 is generally considered to be a new tumor suppressor, the consequence of Pdcd4 deficiency in tumorigenesis is not well established. The role of PDCD4 in colitis-associated colorectal carcinoma (CRC) remains unknown.

METHODS

Experimental colitis and CRC were induced by dextran sodium sulfate and dextran sodium sulfate with azoxymethane, respectively, in wild type and Pdcd4 knockout (Pdcd4(-/-)) mice and were evaluated by clinical examination and histopathology. Levels of cytokines were detected by enzyme-linked immunosorbent assay. Changes in signaling pathways were examined by Western blot and immunofluorescent staining. Cell proliferation was determined by BrdU incorporation and Cell Counting Kit-8 staining.

RESULTS

Pdcd4 deficiency not only aggravated the dextran sodium sulfate-induced acute colitis but also promoted the development of colitis-induced CRC. Mechanically, Pdcd4 deficiency accelerated epithelial cell proliferation during tumorigenesis, markedly up-regulated the expression of proinflammatory cytokines, such as interleukin (IL)-6, and enhanced the activation of signal transducer and activator of transcription (STAT3), a IL-6 downstream effector. Using purified cells, we found that Pdcd4 deficiency increased IL-6 expression in vitro and the susceptibility to IL-6/STAT3 pathway-mediated cell proliferation significantly. Furthermore, blockade of IL-6/STAT3 pathway through sgp130Fc reversed the promoting effect of Pdcd4 deficiency on colonic epithelial cell proliferation in vivo.

CONCLUSION

The Pdcd4 deficiency accelerates colitis and colitis-associated CRC presumably through up-regulating IL-6/STAT3 pathway, suggesting that PDCD4 plays a protective role in inflammation-associated carcinoma and might be a potential target for the treatment of CRC.