Clinicopathological Significance of Decreased Expression of the Tumor Inhibitor Gene PDCD5 in Osteoclastoma

Background: The gene programmed cell death 5 (PDCD5) has recently been characterized as a tumor suppressor gene and is believed to be an important prognostic cancer marker; it is frequently involved in neoplastic transformation and apoptosis of tumor cells. Several studies have demonstrated a decrease or loss of expression of PDCD5 in certain tumors. However, the relevance of PDCD5 expression in human osteoclastoma and its clinicopathological significance have not been extensively studied. Methods: The aim of this study was to explore the relative transcriptional and translational expression levels of PDCD5 in 79 osteoclastoma samples using multi-modal methods of analysis. Results: Our findings showed that 52% (15/29) of osteoclastoma cases exhibited reduced PDCD5 expression at the transcriptional level, and 56% (44/79) exhibited lower PDCD5 expression at the protein level, when compared with nontumor tissue. In addition, the statistical significance of the altered PDCD5 protein expression was examined using the Campanacci grading system for osteoclastoma. More importantly, the decreased expression at the translational level was observed to have a negative association with the Ki-67 staining index. Conclusion: Based on these findings, abnormal PDCD5 expression might be an important biomarker in human osteoclastoma and may contribute to tumor progression and malignant cell proliferation.

PDCD5 regulates cell proliferation, cell cycle progression and apoptosis

Programmed cell death (PDCD)5 is cloned from human leukemia cell line TF-1. PDCD5 is one of the members of the programmed cell death protein family that is frequently involved in tumor growth and apoptosis. To investigate the molecular and cellular functions of PDCD5, the present study established a PDCD5 stably overexpressing A431 cell line and examined the role of PDCD5 in cell proliferation, cell cycle progression and apoptosis. The data demonstrated that overexpression of PDCD5 significantly inhibited cell proliferation, induced cell cycle arrest at G2/M phase and apoptosis in A431 cells. The expression profiles of certain key regulators of these cellular events were further investigated, including P53, B cell lymphoma (BCL)-2, BCL-2 associated X protein (BAX) and caspase (CASP)3. The data demonstrated that at the transcript and protein levels, P53, BAX and CASP3 were all upregulated in the PDCD5 stably overexpressing A431 cells whereas BCL-2 was downregulated, indicating that PDCD5 acts as an important upstream regulator of P53, BCL-2, BAX and CASP3. The data suggest that PDCD5 regulates cell proliferation, cell cycle progression and apoptosis in A431 cells. PDCD5 may be a novel tumor suppressor gene, and may be potentially used for cancer treatment in the future.

Protein serine/threonine phosphatase PPEF-1 suppresses genotoxic stress response via dephosphorylation of PDCD5

Programmed cell death 5 (PDCD5) is believed to play a crucial role in p53 activation; however, the underlying mechanism of how PDCD5 function is regulated during apoptosis remains obscure. Here, we report that the serine/threonine phosphatase PPEF-1 interacts with and dephosphorylates PDCD5 at Ser-119, which leads to PDCD5 destabilization. Overexpression of wild-type PPEF-1, but not inactive PPEF-1^D172N, efficiently suppressed CK2α-mediated stabilization of PDCD5 and p53-mediated apoptosis in response to etoposide (ET). Conversely, PPEF-1 knockdown further enhanced genotoxic stress responses. Notably, PPEF-1 suppressed p53-mediated genotoxic stress response via negative regulation of PDCD5. We also determined that overexpression of wild-type PPEF-1, but not inactive PPEF-1^D172N, significantly increased tumorigenic growth and chemoresistance of A549 human lung carcinoma cells. Collectively, these data demonstrate that PPEF-1 plays a pivotal role in tumorigenesis of lung cancer cells by reducing PDCD5-mediated genotoxic stress responses.

Roles of programmed cell death protein 5 in inflammation and cancer (Review)

PDCD5 (programmed cell death 5) is an apoptosis related gene cloned in 1999 from a human leukemic cell line. PDCD5 protein containing 125 amino acid (aa) residues sharing significant homology to the corresponding proteins of species. Decreased expression of PDCD5 has been found in many human tumors, including breast, gastric cancer, astrocytic glioma, chronic myelogenous leukemia and hepatocellular carcinoma. In recent years, increased number of studies have shown the functions and mechanisms of PDCD5 protein in cancer cells, such as paraptosis, cell cycle and immunoregulation. In the present review, we provide a comprehensive review on the role of PDCD5 in cancer tissues and cells. This review summarizes the recent studies of the roles of PDCD5 in inflammation and cancer. We mainly focus on discoveries related to molecular mechanisms of PDCD5 protein. We also discuss some discrepancies between the current studies. Overall, the current available data will open new perspectives for a better understanding of PDCD5 in cancer.

Diagnostic investigations of DKK-1 and PDCD5 expression levels as independent prognostic markers of human chondrosarcoma

In this study, we investigated the expression levels of Dickkopf-1 (DKK-1) and programmed cell death 5 (PDCD5) by using quantitative real-time PCR and immunohistochemistry in patients with chondrosarcoma. The DKK-1 mRNA levels were significantly higher in chondrosarcoma when compared with the corresponding nontumor tissues (mean ± SD: 4.23 ± 1.54; 1.54 ± 0.87; P = 0.001). PDCD5 mRNA levels were remarkably deceased in tumor tissues when compared with corresponding nontumor tissues (mean ± SD: 1.94 ± 0.73; 5.42 ± 1.73; P = 0.001). The high and moderate DKK-1 expressions were observed for 60% of chondrosarcoma samples in comparison with 27.5% of corresponding nontumor tissues (P  =  0.001). Moreover, low expression of PDCD5 was found in 67.5% of the tumor tissues when compared with the nontumor tissues (32.5%; P = 0.002). The results of this study showed that high DKK-1 expression levels were strongly related to MSTS stage (P = 0.011) and the advancement of histological grade (P < 0.001). Furthermore, the PDCD5 expression levels were correlated with histological grade (P < 0.001), MSTS stage (P = 0.016), and distant metastasis (P = 0.001). Kaplan-Meier survival and log-rank survival showed that patients with high DKK-1 levels and low PDCD5 levels were correlated with shorter overall survival (log-rank test P < 0.001). PDCD5 levels, histological grade, and tumor stage were independent predictors of overall survival. In conclusion, DKK-1 and PDCD5 can be independent predictors of overall survival in patients suffering from chondrosarcoma. © 2016 IUBMB Life, 68(7):597-601, 2016.

Cellular functions of programmed cell death 5

Programmed cell death 5 (PDCD5) was originally identified as an apoptosis-accelerating protein that is widely expressed and has been well conserved during the process of evolution. PDCD5 has complex biological functions, including programmed cell death and immune regulation. It can accelerate apoptosis in different type of cells in response to different stimuli. During this process, PDCD5 rapidly translocates from the cytoplasm to the nucleus. PDCD5 regulates the activities of TIP60, HDAC3, MDM2 and TP53 transcription factors. These proteins form part of a signaling network that is disrupted in most, if not all, cancer cells. Recent evidence suggests that PDCD5 participates in immune regulation by promoting regulatory T cell function via the PDCD5-TIP60-FOXP3 pathway. The stability and expression of PDCD5 are finely regulated by other molecules, such as NF-κB p65, OTUD5, YAF2 and DNAJB1. PDCD5 is phosphorylated by CK2 at Ser119, which is required for nuclear translocation in response to genotoxic stress. In this review, we describe what is known about PDCD5 and its cellular functions.

Bifurcation analysis and potential landscapes of the p53-Mdm2 module regulated by the co-activator programmed cell death 5

The dynamics of p53 play important roles in the regulation of cell fate decisions in response to various stresses, and programmed cell death 5 (PDCD5) functions as a co-activator of p53 that modulates p53 dynamics. In the present paper, we investigated how p53 dynamics are modulated by PDCD5 during the deoxyribose nucleic acid damage response using methods of bifurcation analysis and potential landscape. Our results revealed that p53 activities display rich dynamics under different PDCD5 levels, including monostability, bistability with two stable steady states, oscillations, and the coexistence of a stable steady state (or two states) and an oscillatory state. The physical properties of the p53 oscillations were further demonstrated by the potential landscape in which the potential force attracts the system state to the limit cycle attractor, and the curl flux force drives coherent oscillation along the cyclic trajectory. We also investigated the efficiency with which PDCD5 induced p53 oscillations. We show that Hopf bifurcation can be induced by increasing the PDCD5 efficiency and that the system dynamics exhibited clear transition features in both barrier height and energy dissipation when the efficiency was close to the bifurcation point.

Low programmed cell death 5 expression is a prognostic factor in ovarian cancer

Background:

Ovarian cancer is a leading gynecological malignancy. We investigated the prognostic value of programmed cell death 5 (PDCD5) in patients with ovarian cancer.

Methods:

Expression levels of PDCD5 mRNA and protein were examined in six ovarian cancer cell lines (SKOV3, CAOV3, ES2, OV1, 3AO, and HOC1A) and one normal ovarian epithelial cell line (T29) using reverse transcription polymerase chain reaction, Western blotting, and flow cytometry. After inducing PDCD5 induction in SKOV3 cells or treating this cell line with taxol or doxorubicin (either alone or combined), apoptosis was measured by Annexin V-FITC/propidium iodide staining. Correlations between PDCD5 protein expression and pathological features, histological grade, FIGO stage, effective cytoreductive surgery, and serum cancer antigen-125 values were evaluated in patients with ovarian cancer.

Results:

PDCD5 mRNA and protein expression were downregulated in ovarian cancer cells. Recombinant human PDCD5 increased doxorubicin-induced apoptosis in SKOV3 cells (15.96 ± 2.07%, vs. 3.17 ± 1.45% in controls). In patients with ovarian cancer, PDCD5 expression was inversely correlated with FIGO stage, pathological grade, and patient survival (P < 0.05, R = 0.7139 for survival).

Conclusions:

PDCD5 expression is negatively correlated with disease progression and stage in ovarian cancer. Therefore, measuring PDCD5 expression may be a good method of determining the prognosis of ovarian cancer patients.

The p53 binding protein PDCD5 is not rate-limiting in DNA damage induced cell death

The tumour suppressor p53 is an important mediator of cell cycle arrest and apoptosis in response to DNA damage, acting mainly by transcriptional regulation of specific target genes. The exact details how p53 modulates this decision on a molecular basis is still incompletely understood. One mechanism of regulation is acetylation of p53 on lysine K120 by the histone-acetyltransferase Tip60, resulting in preferential transcription of proapoptotic target genes. PDCD5, a protein with reported pro-apoptotic function, has recently been identified as regulator of Tip60-dependent p53-acetylation. In an effort to clarify the role of PDCD5 upon DNA damage, we generated cell lines in which PDCD5 expression was conditionally ablated by shRNAs and investigated their response to genotoxic stress. Surprisingly, we failed to note a rate-limiting role of PDCD5 in the DNA damage response. PDCD5 was dispensable for DNA damage induced apoptosis and cell cycle arrest and we observed no significant changes in p53 target gene transcription. While we were able to confirm interaction of PDCD5 with p53, we failed to do so for Tip60. Altogether, our results suggest a role of PDCD5 in the regulation of p53 function but unrelated to cell cycle arrest or apoptosis, at least in the cell types investigated.

Effect of the HBV whole-X gene on the expression of hepatocellular carcinoma associated proteins

BACKGROUND

The hepatitis B virus (HBV) pre-X gene resides upstream of the HBV X gene, and together they form the HBV whole-X gene. Although it has been evident that the HBV whole-X protein is involved in the development of hepatocellular carcinoma, its biological role and molecular mechanism remain largely unknown.

METHODS

In this study, we subcloned the HBV whole-X gene and constructed a HBV whole-X expressing vector. After transfection of the HBV whole-X gene into HL-7702 cells, the profile of the differential cellular protein composition in the cells was analyzed by using two-dimensional electrophoresis coupled to matrix-assisted laser desorption/ionization-time of flight mass spectrometry.

RESULTS

The results showed that 18 major proteins were differentially expressed in the cells transfected with or without the HBV whole-X gene. The expression of these genes was further confirmed by reverse transcription-polymerase chain reaction and Western blot analysis.

CONCLUSION

Our findings provide a new insight into the investigation of the pathological role that the HBV whole-X gene plays in the development of hepatocellular carcinoma and may lead to the design of novel strategies for the treatment of this disease.

Serum programmed cell death protein 5 (PDCD5) levels is upregulated in liver diseases

Intracellular protein molecules are detected in the blood following release from damaged cells. PDCD5 is widely expressed in most types of normal human tissue and is unregulated in cells undergoing apoptosis. It is therefore hypothesized that release of PDCD5 into the circulation might be a specific marker of apoptosis. In this study, a sandwich ELISA was developed for quantification of soluble PDCD5 protein and used to investigate serum PDCD5 levels in liver diseases. The highest levels of PDCD5 were detected in acute icteric hepatitis (AIH) patients compared with normal subjects and other detected liver diseases, such as chronic active hepatitis B (CAHB), chronic persistent hepatitis B (CPHB) and and liver cirrhosis (LC). Increased PDCD5 levels correlated well with ALT and AST in AIH and CAHB patients. In patients with CPHB, increased PDCD5 levels correlated well with AST, TBI, DBIL, and IBIL. In LC patients, PDCD5 levels correlated well with AST/ALT and DBIL. More importantly, increased PDCD5 levels were also observed in patients with normal ALT or AST levels. These data demonstrate a correlation between increased levels of PDCD5 in serum and liver disease progression and indicate the potential utility of serum PDCD5 as a biomarker for monitoring liver injury.

PDCD5 negatively regulates autoimmunity by upregulating FOXP3(+) regulatory T cells and suppressing Th17 and Th1 responses

Maintenance of FOXP3 protein expression is crucial for differentiation and maturation of regulatory T (Treg) cells, which play important roles in immune homeostasis and immune tolerance. We demonstrate here that PDCD5 interacts with FOXP3, increases acetylation of FOXP3 in synergy with Tip60 and enhances the repressive function of FOXP3. In PDCD5 transgenic (PDCD5tg) mice, overexpression of PDCD5 enhanced the level of FOXP3 protein and percentage of CD4(+)CD25(+)FOXP3(+) cells. Naïve CD4(+) T cells from PDCD5tg mice were more sensitive to TGF-β-induced Treg polarization and expansion. These induced Tregs retained normal suppressive function in vitro. Severity of experimentally-induced autoimmune encephalomyelitis (EAE) in PDCD5tg mice was significantly reduced relative to that of wild-type mice. The beneficial effect of PDCD5 likely resulted from increases of Treg cell frequency, accompanied by a reduction of the predominant pathogenic Th17/Th1 response. Activation-induced cell death enhanced by PDCD5 was also linked to this process. This is the first report revealing that PDCD5 activity in T cells suppresses autoimmunity by modulating Tregs. This study suggests that PDCD5 serves as a guardian of immunological functions and that the PDCD5-FOXP3-Treg axis may be a therapeutic target for autoimmunity.

Transfection of PDCD5 effect on the biological behavior of tumor cells and sensitized gastric cancer cells to cisplatin-induced apoptosis

BACKGROUND

Programmed cell death 5 (PDCD5) expression is reduced in various human tumor cells, and the protein concentration and nuclear translocation of PDCD5 is also observed during tumor cell apoptosis.

AIMS

The purpose of this study was to investigate the differential expression of PDCD5 in six gastric cell lines, and to explore the changes of biological behavior mechanism underlying enhanced apoptosis-inducing effects of cisplatin by PDCD5 over-expression on gastric cancer BGC823 cells.

METHODS

RT-PCR and real-time PCR were used to determine PDCD5 expression. BGC823/PDCD5 cells were assessed the cellular proliferating ability by MTT assay, soft agar cloning experiments and tumorigenicity in nude mice experiments in vivo. The effects of cisplatin in combination with PDCD5 on the proliferation and apoptosis were measured by MTT, Annexin-V-FITC/PI dual labeling and cell cycle analysis, respectively. Immunofluorescence was used to detect co-localization of p53 and PDCD5 protein to explore the mechanism underlying the synergistic therapeutic effect of PDCD5 with cisplatin (5 μg/ml for 24 h).

RESULTS

PDCD5 had the highest expression level in the GES1 cell among other cell lines. The growths of BGC823 cells transfected with PDCD5 for six (6th) or 17 (17th) days were both slower than that of BGC823 and BGC823/Neo (P < 0.01). The stable transfection of PDCD5 demonstrated G2/M cell cycle arrest, increased apoptosis and nuclear translocation of PDCD5 and p53 after cisplatin treatment.

CONCLUSIONS

Stable transfection of the PDCD5 gene can inhibit the growth of the BGC823 cell line and notably improve apoptosis-inducing effects of cisplatin, indicating a novel strategy for better chemotherapeutic effects on gastric cancer.

PDCD5 promotes cisplatin-induced apoptosis of glioma cells via activating mitochondrial apoptotic pathway

Glioma is one of the most common primary brain tumors. Despite surgical resection, radiotherapy, and chemotherapy, the prognosis of patients with malignant glioma remains poor. Programmed cell death 5 (PDCD5) is a newly described pro-apoptotic protein. Our previous study showed that PDCD5 downregulation in gliomas was associated with higher pathological grade. Here, we investigated the effect of PDCD5 on chemosensitivity of glioma cells and its mechanism. We demonstrated that overexpression or knockdown of PDCD5 had no significant effect on the proliferation of glioma cell lines (U87, U251, and T98G) in the absence of chemotherapeutic agents. However, PDCD5 overexpression effectively sensitized U87 cells to chemotherapeutic drugs (cisplatin, carboplatin, and vincristine) in a concentration-dependent manner, while its knockdown resulted in decreased chemosensitivity in U251, T98G, and U87 cells. Importantly, expression of PDCD5 also markedly inhibited tumor cell proliferation and colony formation in the presence of low doses of cisplatin. Furthermore, we found that PDCD5 expression promoted cisplatin-induced apoptosis, increased markedly the activation of caspase-3 and caspase-9, and decreased significantly the ratio of Bcl-2/Bax proteins, but had no effect on the activation of caspase-8. Taken together, our findings indicate that PDCD5 promotes chemosensitivity by activating mitochondria-related apoptotic pathway, and that the combination of PDCD5 and chemotherapeutic drugs such as cisplatin, is expected to be an effective therapeutic strategy for the malignant glioma.

PDCD5-regulated cell fate decision after ultraviolet-irradiation-induced DNA damage

Programmed cell death 5 (PDCD5) is a human apoptosis-related molecule that is involved in both the cytoplasmic caspase-3 activity pathway (by regulating Bax translocation from cytoplasm to mitochondria) and the nuclear pathway (by interacting with Tip60). In this study, we developed a mathematical model of the PDCD5-regulated switching of the cell response from DNA repair to apoptosis after ultraviolet irradiation-induced DNA damage. We established the model by combining several hypotheses with experimental observations. Our simulations indicate that the ultimate cell response to DNA damage is dependent on a signal threshold mechanism, and the PDCD5 promotion of Bax translocation plays an essential role in PDCD5-regulated cell apoptosis. Furthermore, the model simulations revealed that PDCD5 nuclear translocation can attenuate cell apoptosis, and PDCD5 interactions with Tip60 can accelerate DNA damage-induced apoptosis, but the final cell fate decision is insensitive to the PDCD5-Tip60 interaction. These results are consistent with experimental observations. The effect of recombinant human PDCD5 was also investigated and shown to sensitize cells to DNA damage by promoting caspase-3 activity.