Cytoplasmic localization of programmed cell death 4 contributes to its anti-apoptotic function

PDCD4 restricts PRRSV replication in an eIF4A-dependent manner and is antagonized by the viral nonstructural protein 9

As obligate parasites, viruses have evolved multiple strategies to evade the host immune defense. Manipulation of the host proteasome system to degrade specific detrimental factors is a common viral countermeasure. To identify host proteins targeted for proteasomal degradation by porcine reproductive and respiratory syndrome virus (PRRSV), we conducted a quantitative proteomics screen of PRRSV-infected Marc-145 cells under the treatment with proteasome inhibitor MG132. The data revealed that the expression levels of programmed cell death 4 (PDCD4) were strongly downregulated by PRRSV and significantly rescued by MG132. Further investigation confirmed that PRRSV infection induced the translocation of PDCD4 from the nucleus to the cytoplasm, and the viral nonstructural protein 9 (Nsp9) promoted PDCD4 proteasomal degradation in the cytoplasm by activating the Akt-mTOR-S6K1 pathway. The C-terminal domain of Nsp9 was responsible for PDCD4 degradation. As for the role of PDCD4 during PRRSV infection, we demonstrated that PDCD4 knockdown favored viral replication, while its overexpression significantly attenuated replication, suggesting that PDCD4 acts as a restriction factor for PRRSV. Mechanistically, we discovered eukaryotic translation initiation factor 4A (eIF4A) was required for PRRSV. PDCD4 interacted with eIF4A through four sites (E249, D253, D414, and D418) within its two MA3 domains, disrupting eIF4A-mediated translation initiation in the 5'-untranslated region of PRRSV, thereby inhibiting PRRSV infection. Together, our study reveals the antiviral function of PDCD4 and the viral strategy to antagonize PDCD4. These results will contribute to our understanding of the immune evasion strategies employed by PRRSV and offer valuable insights for developing new antiviral targets.IMPORTANCEPorcine reproductive and respiratory syndrome virus (PRRSV) infection results in major economic losses in the global swine industry and is difficult to control effectively. Here, using a quantitative proteomics screen, we identified programmed cell death 4 (PDCD4) as a host protein targeted for proteasomal degradation by PRRSV. We demonstrated that PDCD4 restricts PRRSV replication by interacting with eukaryotic translation initiation factor 4A, which is required for translation initiation in the viral 5'-untranslated region. Additionally, four sites within two MA3 domains of PDCD4 are identified to be responsible for its antiviral function. Conversely, PRRSV nonstructural protein 9 promotes PDCD4 proteasomal degradation in the cytoplasm by activating the Akt-mTOR-S6K1 pathway, thus weakening the anti-PRRSV function. Our work unveils PDCD4 as a previously unrecognized host restriction factor for PRRSV and reveals that PRRSV develops countermeasures to overcome PDCD4. This will provide new insights into virus-host interactions and the development of new antiviral targets.

Mapping the function of MicroRNAs as a critical regulator of tumor-immune cell communication in breast cancer and potential treatment strategies

Among women, breast cancer ranks as the most prevalent form of cancer, and the presence of metastases significantly reduces prognosis and diminishes overall survival rates. Gaining insights into the biological mechanisms governing the conversion of cancer cells, their subsequent spread to other areas of the body, and the immune system's monitoring of tumor growth will contribute to the advancement of more efficient and targeted therapies. MicroRNAs (miRNAs) play a critical role in the interaction between tumor cells and immune cells, facilitating tumor cells' evasion of the immune system and promoting cancer progression. Additionally, miRNAs also influence metastasis formation, including the establishment of metastatic sites and the transformation of tumor cells into migratory phenotypes. Specifically, dysregulated expression of these genes has been associated with abnormal expression of oncogenes and tumor suppressor genes, thereby facilitating tumor development. This study aims to provide a concise overview of the significance and function of miRNAs in breast cancer, focusing on their involvement as tumor suppressors in the antitumor immune response and as oncogenes in metastasis formation. Furthermore, miRNAs hold tremendous potential as targets for gene therapy due to their ability to modulate specific pathways that can either promote or suppress carcinogenesis. This perspective highlights the latest strategies developed for miRNA-based therapies.

Identification of reactive oxygen species that induce spoptosis, a novel and distinctive mode of regulated cell death

Using some solutions activated by irradiation with non-thermal atmospheric pressure plasma (NTAPP), we had discovered that a new and distinctive mode of cell death, named spoptosis, exists in cells, the induction of which involves the action of reactive oxygen species (ROS). However, it was unknown what types of ROS and how they trigger the cell death. When cells were treated with a higher dose of Ascorbic acid (AA) generating O₂^- and H₂O₂ or Antimycin A (AM) generating O₂^-, cell death occurred along with cellular shrinkage, Pdcd4 disappearance, and vesicle formation. Only in cells treated with AA, genomic DNA was digested irregularly and membrane permeability increased aberrantly. On the other hand, cells treated with a higher dose of H₂O₂ displayed cell death and cellular shrinkage but not the other events, and those treated with a lower dose of H₂O₂ displayed cell death but not the other events. Strikingly, when cells underwent double treatment with AM and H₂O₂, the events, which had not been observed by their single treatment, became compensated. All the events were suppressed with an antioxidant, confirming that they were mediated by ROS. Thus, the mode of cell death induced by AA or combination of AM and H₂O₂ was consistent with that of cell death by NTAPP-activated solutions. These results suggested that O₂^- and H₂O₂ collaboratively trigger spoptotic cell death with the associated events, and that AA and combination of AM and H₂O₂ are functionally alternative in place of NTAPP-activated solutions.

A novel and distinctive mode of cell death revealed by using non-thermal atmospheric pressure plasma: The involvements of reactive oxygen species and the translation inhibitor Pdcd4

Cells death is indispensable for embryonic development, tissue homeostasis, and the elimination of cancer, virally infected, or degenerated cells in multicellular organisms. It occurs not only via existing modes but also via unidentified modes, whose elucidation requires. Exposure to non-thermal atmospheric pressure plasma (NTAPP) has been demonstrated to induce cell death, probably because of its ability to generate reactive oxygen species (ROS). However, the mode of this cell death and its underlying mechanism remained elusive. Here we show cell death occurring in a novel and distinctive mode different from apoptosis and necrosis/necroptosis through a mechanism that ROS mediate the loss of the translation inhibitor Programmed cell death 4 (Pdcd4) when cells are cultured in solutions activated by NTAPP irradiation. Thus, our study performed with NTAPP-activated solutions may provide insight into the existence of the atypical cell death in cells and some features of its distinguishing mode and underlying mechanism.

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.

MicroRNA-182 Promotes Cell Migration by Targeting Programmed Cell Death 4 in Hepatocellular Carcinoma Cells

Purpose

Hepatocellular carcinoma (HCC) is the most common primary liver tumor and the third greatest cause of cancer-related death worldwide. Programmed cell death 4 (PDCD4) was reported as a potential tumor-suppressor in hepatocarcinogenesis. However, relatively little is known about mechanisms that regulate PDCD4 expression in HCC. The aim of the present study is to investigate the expression of PDCD4 and miR-182 in human HCC cell lines and clinical HCC specimens and determine whether PDCD4 is a direct target of miR-182 in HCC cell lines.

Materials

The expression of miR-182 and PDCD4 in human HCC cell lines and HCC tissues were examined using qRT-PCR and Western blot method. Transwell and wound healing assays were carried out to explore the influence of miR-182 on hepatoma cells migration. A luciferase reporter assay was conducted to confirm target association.

Results

In our research, we found that PDCD4 was downregulated, whereas miR-182 was upregulated in liver cancer cell lines and HCC tissues. Transwell and wound healing assays illustrated that miR-182 contributed to migration activities of liver cancer cell lines. Loss or increase of miR-182 can lead to a negative expression of PDCD4 protein level. The luciferase reporter assay showed that PDCD4 is a direct target of miR-182.

Conclusion

All these findings suggest that miR-182 may act as an oncogenic role in liver cancer cells by directly and negatively regulating expression of PDCD4.