Multifaceted roles of PDCD6 both within and outside the cell

Programmed cell death protein 6 (PDCD6) is an evolutionarily conserved Ca2+ -binding protein. PDCD6 is involved in regulating multifaceted and pleiotropic cellular processes in different cellular compartments. For instance, nuclear PDCD6 regulates apoptosis and alternative splicing. PDCD6 is required for coat protein complex II-dependent endoplasmic reticulum-to-Golgi apparatus vesicular transport in the cytoplasm. Recent advances suggest that cytoplasmic PDCD6 is involved in the regulation of cytoskeletal dynamics and innate immune responses. Additionally, membranous PDCD6 participates in membrane repair through endosomal sorting complex required for transport complex-dependent membrane budding. Interestingly, extracellular vesicles are rich in PDCD6. Moreover, abnormal expression of PDCD6 is closely associated with many diseases, especially cancer. PDCD6 is therefore a multifaceted but pivotal protein in vivo. To gain a more comprehensive understanding of PDCD6 functions and to focus and stimulate PDCD6 research, this review summarizes key developments in its role in different subcellular compartments, processes, and pathologies.

PDCD6 Promotes Hepatocellular Carcinoma Cell Proliferation and Metastasis through the AKT/GSK3β/β-catenin Pathway

OBJECTIVE

Programmed cell death 6 (PDCD6), a Ca ²⁺-binding protein, has been reported to be aberrantly expressed in all kinds of tumors. The aim of this study was to explore the role and mechanism of PDCD6 in hepatocellular carcinomas (HCCs).

METHODS

The expression levels of PDCD6 in liver cancer patients and HCC cell lines were analyzed using bioinformatics and Western blotting. Cell viability and metastasis were determined by methylthiazol tetrazolium (MTT) and transwell assays, respectively. And Western blotting was used to test related biomarkers and molecular pathway factors in HCC cell lines. LY294002, a PI3K inhibitor inhibiting AKT, was used to suppress the AKT/GSK3β/β-catenin pathway to help evaluate the role of this pathway in the HCC carcinogenesis associated with PDCD6.

RESULTS

The analysis of The Cancer Genome Atlas Database suggested that high PDCD6 expression levels were relevant to liver cancer progression. This was consistent with our finding of higher levels of PDCD6 expression in HCC cell lines than in normal hepatocyte cell lines. The results of MTT, transwell migration, and Western blotting assays revealed that overexpression of PDCD6 positively regulated HCC cell proliferation, migration, and invasion. Conversely, the upregulation of PDCD6 expression in the presence of an AKT inhibitor inhibited HCC cell proliferation, migration, and invasion. In addition, PDCD6 promoted HCC cell migration and invasion by epithelial-mesenchymal transition. The mechanistic investigation proved that PDCD6 acted as a tumor promoter in HCC through the AKT/GSK3β/β-catenin pathway, increasing the expression of transcription factors and cellular proliferation and metastasis.

CONCLUSION

PDCD6 has a tumor stimulative role in HCC mediated by AKT/GSK3β/β-catenin signaling and might be a potential target for HCC progression.

Analysis of Dysferlin Direct Interactions with Putative Repair Proteins Links Apoptotic Signaling to Ca2+ Elevation via PDCD6 and FKBP8

Quantitative surface plasmon resonance (SPR) was utilized to determine binding strength and calcium dependence of direct interactions between dysferlin and proteins likely to mediate skeletal muscle repair, interrupted in limb girdle muscular dystrophy type 2B/R2. Dysferlin canonical C2A (cC2A) and C2F/G domains directly interacted with annexin A1, calpain-3, caveolin-3, affixin, AHNAK1, syntaxin-4, and mitsugumin-53, with cC2A the primary target and C2F lesser involved, overall demonstrating positive calcium dependence. Dysferlin C2 pairings alone showed negative calcium dependence in almost all cases. Like otoferlin, dysferlin directly interacted via its carboxy terminus with FKBP8, an anti-apoptotic outer mitochondrial membrane protein, and via its C2DE domain with apoptosis-linked gene (ALG-2/PDCD6), linking anti-apoptosis with apoptosis. Confocal Z-stack immunofluorescence confirmed co-compartmentalization of PDCD6 and FKBP8 at the sarcolemmal membrane. Our evidence supports the hypothesis that prior to injury, dysferlin C2 domains self-interact and give rise to a folded, compact structure as indicated for otoferlin. With elevation of intracellular Ca²⁺ in injury, dysferlin would unfold and expose the cC2A domain for interaction with annexin A1, calpain-3, mitsugumin 53, affixin, and caveolin-3, and dysferlin would realign from its interactions with PDCD6 at basal calcium levels to interact strongly with FKBP8, an intramolecular rearrangement facilitating membrane repair.

Identification of Important Factors Causing Developmental Arrest in Cloned Pig Embryos by Embryo Biopsy Combined with Microproteomics

The technique of pig cloning holds great promise for the livestock industry, life science, and biomedicine. However, the prenatal death rate of cloned pig embryos is extremely high, resulting in a very low cloning efficiency. This limits the development and application of pig cloning. In this study, we utilized embryo biopsy combined with microproteomics to identify potential factors causing the developmental arrest in cloned pig embryos. We verified the roles of two potential regulators, PDCD6 and PLK1, in cloned pig embryo development. We found that siRNA-mediated knockdown of PDCD6 reduced mRNA and protein expression levels of the pro-apoptotic gene, CASP3, in cloned pig embryos. PDCD6 knockdown also increased the cleavage rate and blastocyst rate of cloned porcine embryos. Overexpression of PLK1 via mRNA microinjection also improved the cleavage rate of cloned pig embryos. This study provided a new strategy to identify key factors responsible for the developmental defects in cloned pig embryos. It also helped establish new methods to improve pig cloning efficiency, specifically by correcting the expression pattern of PDCD6 and PLK1 in cloned pig embryos.

The Contribution of PDCD6 Polymorphisms to Oral Cancer Risk

BACKGROUND/AIM

Programmed cell death 6 (PDCD6) is up-regulated and highly expressed in early apoptotic cells. In several types of cancer, such as cervical, breast and lung cancers, the association of PDCD6 genotypes have been investigated. However, the contribution of PDCD6 variant genotypes to oral cancer has never been examined. The current study aimed to evaluate the contribution of the PDCD6 rs4957014 and rs3756712 genotypes to the risk of oral cancer in Taiwan.

PATIENTS AND METHODS

The contribution of PDCD6 genotypes to oral cancer risk was examined among 958 patients with lung cancer and 958 age- and sex-matched healthy controls by polymerase chain reaction-restriction fragment length polymorphism (PCR- RFLP).

RESULTS

The data showed that the hetero-variant GT and homo-variant GG genotypes of PDCD6 rs4957014 were associated with a decreased risk of oral cancer [odds ratio (OR)=0.81 and 0.39, 95% confidence interval (CI)=0.67-0.97 and 0.27-0.56, respectively]. The recessive and dominant models also showed that G carriers have protective effects (OR=0.43 and 0.72, 95% CI=0.30-0.61 and 0.61-0.87, respectively). The analysis of allelic frequency distributions showed that the G allele of PDCD6 rs4957014 was associated with reduced oral cancer risk (OR=0.71, 95% CI=0.62-0.82). There was no significant association between any PDCD6 rs3756712 genotype and oral cancer risk. In addition, the GG genotype at PDCD6 rs4957014 significantly decreased the risk of oral cancer among both males (adjusted OR=0.31, 95%CI=0.24-0.56) and females (adjusted OR=0.44, 95% CI=0.22-0.91). Furthermore, the GG genotype at PDCD6 rs4957014 significantly decreased the risk of oral cancer among smokers (adjusted OR=0.35, 95% CI=0.22-0.58), alcohol drinkers (adjusted OR=0.33, 95% CI=0.18-0.49), non-betel quid chewers (adjusted OR=0.33, 95% CI=0.17- 0.81), betel quid chewers (adjusted OR=0.34, 95% CI=0.21- 0.59), but not among never-smokers and non-alcohol drinkers.

CONCLUSION

The G allele carriers of PDCD6 rs4957014 may have protective effects on oral cancer risk and serve as a practical marker for early detection of oral cancer in Taiwan.

Interplay in neural functions of cell adhesion molecule close homolog of L1 (CHL1) and Programmed Cell Death 6 (PDCD6)

Close homolog of L1 (CHL1) is a cell adhesion molecule of the immunoglobulin superfamily. It promotes neuritogenesis and survival of neurons in vitro. In vivo, CHL1 promotes nervous system development, regeneration after trauma, and synaptic function and plasticity. We identified programmed cell death 6 (PDCD6) as a novel binding partner of the CHL1 intracellular domain (CHL1-ICD). Co-immunoprecipitation, pull-down assay with CHL1-ICD, and proximity ligation in cerebellum and pons of 3-day-old and 6-month-old mice, as well as in cultured cerebellar granule neurons and cortical astrocytes indicate an association between PDCD6 and CHL1. The Ca2+-chelator BAPTA-AM inhibited the association between CHL1 and PDCD6. The treatment of cerebellar granule neurons with a cell-penetrating peptide comprising the cell surface proximal 30 N-terminal amino acids of CHL1-ICD inhibited the association between CHL1 and PDCD6 and PDCD6- and CHL1-triggered neuronal survival. These results suggest that PDCD6 contributes to CHL1 functions in the nervous system.

An epithelial-mesenchymal transition-related 5-gene signature predicting the prognosis of hepatocellular carcinoma patients

Background

Tumor metastasis is one of the leading reasons of the dismal prognosis of hepatocellular carcinoma (HCC). Epithelial-mesenchymal transition (EMT) is closely associated with tumor metastasis including HCC. The purpose of this study is to construct and validate an EMT-related gene signature for predicting the prognosis of HCC patients.

Methods

Gene expression data of HCC patients was downloaded from The Cancer Genome Atlas (TCGA) database. Gene set enrichment analysis (GSEA) was performed to found the EMT-related gene sets which were obviously distinct between normal samples and paired HCC samples. Cox regression analysis was used to develop an EMT-related prognostic signature, and the performance of the signature was evaluated by Kaplan–Meier curves and time-dependent receiver operating characteristic (ROC) curves. A nomogram incorporating the independent predictors was established. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the expression levels of the hub genes in HCC cell lines, and the role of PDCD6 in the metastasis of HCC was determined by functional experiments.

Results

An EMT-related 5-gene signature (PDCD6, TCOF1, TRIM28, EZH2 and FAM83D) was constructed using univariate and multivariate Cox regression analysis. Based on the signature, the HCC patients were classified into high- and low-risk groups, and patients in high-risk group had a poor prognosis. Time-dependent ROC and Cox regression analyses suggested that the signature could predict HCC prognosis exactly and independently. The predictive capacity of the signature was also validated in two external cohorts. GSEA results showed that many cancer-related signaling pathways such as PI3K/Akt/mTOR pathway and TGF-β/SMAD pathway were enriched in high-risk group. The result of qRT-PCR revealed that PDCD6, TCOF1 and FAM83D were highly expressed in HCC cancer cells. Among them, PDCD6 were found to promote cell migration and invasion.

Conclusion

The EMT-related 5-gene signature can serve as a promising prognostic biomarker for HCC patients and may provide a novel mechanism of HCC metastasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-01864-5.

The Novel ALG-2 Target Protein CDIP1 Promotes Cell Death by Interacting with ESCRT-I and VAPA/B

Apoptosis-linked gene 2 (ALG-2, also known as PDCD6) is a member of the penta-EF-hand (PEF) family of Ca²⁺-binding proteins. The murine gene encoding ALG-2 was originally reported to be an essential gene for apoptosis. However, the role of ALG-2 in cell death pathways has remained elusive. In the present study, we found that cell death-inducing p53 target protein 1 (CDIP1), a pro-apoptotic protein, interacts with ALG-2 in a Ca²⁺-dependent manner. Co-immunoprecipitation analysis of GFP-fused CDIP1 (GFP-CDIP1) revealed that GFP-CDIP1 associates with tumor susceptibility gene 101 (TSG101), a known target of ALG-2 and a subunit of endosomal sorting complex required for transport-I (ESCRT-I). ESCRT-I is a heterotetrameric complex composed of TSG101, VPS28, VPS37 and MVB12/UBAP1. Of diverse ESCRT-I species originating from four VPS37 isoforms (A, B, C, and D), CDIP1 preferentially associates with ESCRT-I containing VPS37B or VPS37C in part through the adaptor function of ALG-2. Overexpression of GFP-CDIP1 in HEK293 cells caused caspase-3/7-mediated cell death. In addition, the cell death was enhanced by co-expression of ALG-2 and ESCRT-I, indicating that ALG-2 likely promotes CDIP1-induced cell death by promoting the association between CDIP1 and ESCRT-I. We also found that CDIP1 binds to vesicle-associated membrane protein-associated protein (VAP)A and VAPB through the two phenylalanines in an acidic tract (FFAT)-like motif in the C-terminal region of CDIP1, mutations of which resulted in reduction of CDIP1-induced cell death. Therefore, our findings suggest that different expression levels of ALG-2, ESCRT-I subunits, VAPA and VAPB may have an impact on sensitivity of anticancer drugs associated with CDIP1 expression.

miR-9875 functions in antiviral immunity by targeting PDCD6 in mud crab (Scylla paramamosain)

Programmed cell death 6 (PDCD6) is a well-known apoptosis regulator that is involved in the immunity of mammals. However, the effects of miRNA-mediated regulation of PDCD6 expression on apoptosis and virus infection in organisms, especially in marine invertebrates, have not been extensively explored. In this study, PDCD6 of mud crab (Scylla paramamosain) (Sp-PDCD6) was characterized. The results showed that Sp-PDCD6 contains five EF-hands domains and could suppress virus infection via apoptosis promotion. It also presented that Sp-PDCD6 was directly targeted by miR-9875 in vitro and in vivo, miR-9875 served as a positive regulator during the virus invasion. The findings indicated that the miR-9875-PDCD6 pathway possessed fundamental effects on the immune response to virus infection in mud crab. Therefore, our research provided a novel insight into the roles of both miR-9875 and PDCD6 in the regulation of apoptosis and virus defense in mud crab.

The Penta-EF-Hand ALG-2 Protein Interacts with the Cytosolic Domain of the SOCE Regulator SARAF and Interferes with Ubiquitination

ALG-2 is a penta-EF-hand Ca²⁺-binding protein and interacts with a variety of proteins in mammalian cells. In order to find new ALG-2-binding partners, we searched a human protein database and retrieved sequences containing the previously identified ALG-2-binding motif type 2 (ABM-2). After selecting 12 high-scored sequences, we expressed partial or full-length GFP-fused proteins in HEK293 cells and performed a semi-quantitative in vitro binding assay. SARAF, a negative regulator of store-operated Ca²⁺ entry (SOCE), showed the strongest binding activity. Biochemical analysis of Strep-tagged and GFP-fused SARAF proteins revealed ubiquitination that proceeded during pulldown assays under certain buffer conditions. Overexpression of ALG-2 interfered with ubiquitination of wild-type SARAF but not ubiquitination of the F228S mutant that had impaired ALG-2-binding activity. The SARAF cytosolic domain (CytD) contains two PPXY motifs targeted by the WW domains of NEDD4 family E3 ubiquitin ligases. The PPXY motif proximal to the ABM-2 sequence was found to be more important for both in-cell ubiquitination and post-cell lysis ubiquitination. A ubiquitination-defective mutant of SARAF with Lys-to-Arg substitutions in the CytD showed a slower degradation rate by half-life analysis. ALG-2 promoted Ca²⁺-dependent CytD-to-CytD interactions of SARAF. The ALG-2 dimer may modulate the stability of SARAF by sterically blocking ubiquitination and by bridging SARAF molecules at the CytDs.

PDCD6 cooperates with C-Raf to facilitate colorectal cancer progression via Raf/MEK/ERK activation

Background

Colorectal cancer (CRC) is one of the most common malignancies, and it’s expected that the CRC burden will substantially increase in the next two decades. New biomarkers for targeted treatment and associated molecular mechanism of tumorigenesis remain to be explored. In this study, we investigated whether PDCD6 plays an oncogenic role in colorectal cancer and its underlying mechanism.

Methods

Programmed cell death protein 6 (PDCD6) expression in CRC samples were analyzed by immunohistochemistry and immunofluorescence. The prognosis between PDCD6 and clinical features were analyzed. The roles of PDCD6 in cellular proliferation and tumor growth were measured by using CCK8, colony formation, and tumor xenograft in nude mice. RNA-sequence (RNA-seq), Mass Spectrum (MS), Co-Immunoprecipitation (Co-IP) and Western blot were utilized to investigate the mechanism of tumor progression. Immunohistochemistry (IHC) and quantitative real-time PCR (qRT-PCR) were performed to determine the correlation of PDCD6 and MAPK pathway.

Results

Higher expression levels of PDCD6 in tumor tissues were associated with a poorer prognosis in patients with CRC. Furthermore, PDCD6 increased cell proliferation in vitro and tumor growth in vivo. Mechanistically, RNA-seq showed that PDCD6 could affect the activation of the MAPK signaling pathway. PDCD6 interacted with c-Raf, resulting in the activation of downstream c-Raf/MEK/ERK pathway and the upregulation of core cell proliferation genes such as MYC and JUN.

Conclusions

These findings reveal the oncogenic effect of PDCD6 in CRC by activating c-Raf/MEK/ERK pathway and indicate that PDCD6 might be a potential prognostic indicator and therapeutic target for patients with colorectal cancer.

Association of PDCD6 polymorphisms with the risk of cancer: Evidence from a meta-analysis

This study was designed to evaluate the relationship between Programmed cell death protein 6 (PDCD6) polymorphisms and cancer susceptibility. The online databases were searched for relevant case-control studies published up to November 2017. Review Manage (RevMan) 5.3 was used to conduct the statistical analysis. The pooled odds ratio (OR) with its 95% confidence interval (CI) was employed to calculate the strength of association. Overall, our results indicate that PDCD6 rs3756712 T>G polymorphism was significantly associated with decreased risk of cancer under codominant (OR = 0.82, 95%CI = 0.70-0.96, p = 0.01, TG vs TT; OR = 0.53, 95%CI = 0.39-0.72, p < 0.0001, GG vs TT), dominant (OR = 0.76, 95%CI = 0.66-0.89, p = 0.0004, TG+GG vs TT), recessive (OR = 0.57, 95%CI = 0.43-0.78, p = 0.0003, GG vs TT+TG), and allele (OR = 0.76, 95%CI = 0.67-0.86, p < 0.00001, G vs T) genetic model. The finding did not support an association between rs4957014 T>G polymorphism of PDCD6, and different cancers risk.

Up-regulation of miR-20a by HPV16 E6 exerts growth-promoting effects by targeting PDCD6 in cervical carcinoma cells

OBJECTIVE

MicroRNAs (miRNAs/miRs) have been reported to participate in progression of multiple tumors including cervical cancer. High-risk human papillomavirus (HPV) type 16 (HPV16) is the most common and lethal HPV type, leading to exceeding 50% of cervical cancer cases. However, the relationship between miRNA and HPV-induced cervical carcinogenesis remains elusive.

RESULTS

Here, HPV16 E6 positively regulated miR-20a expression. Overexpression of miR-20a showed growth-promoting effects on C33A cells (HPV16-negative), and knockdown of miR-20a showed growth-inhibitory effects on CaSki cells (HPV16-positive). In addition, PDCD6 was identified as a target gene of miR-20a. Overexpression of PDCD6 exerted growth-inhibitory effects (opposite to miR-20a overexpression), which could be reversed by miR-20a overexpression. More importantly, activation of AKT and p38 was observed in C33A cells overexpressing miR-20a, and the growth-promoting action of miR-20a could be abated by p38 inhibition.

CONCLUSION

Up-regulation of miR-20a by HPV16 E6 exerted growth-promoting effects by targeting PDCD6 in cervical carcinoma cells. This study demonstrated miR-20a might be a potential therapeutic target in HPV16 E6 infection type of cervical cancer.

Nanoluciferase Reporter Gene System Directed by Tandemly Repeated Pseudo-Palindromic NFAT-Response Elements Facilitates Analysis of Biological Endpoint Effects of Cellular Ca2+ Mobilization

NFAT is a cytoplasm-localized hyper-phosphorylated transcription factor that is activated through dephosphorylation by calcineurin, a Ca²⁺/calmodulin-dependent phosphatase. A non-palindromic NFAT-response element (RE) found in the IL2 promoter region has been commonly used for a Ca²⁺-response reporter gene system, but requirement of concomitant activation of AP-1 (Fos/Jun) often complicates the interpretation of obtained results. A new nanoluciferase (NanoLuc) reporter gene containing nine-tandem repeats of a pseudo-palindromic NFAT-RE located upstream of the IL8 promoter was designed to monitor Ca²⁺-induced transactivation activity of NFAT in human embryonic kidney (HEK) 293 cells by measuring luciferase activities of NanoLuc and co-expressed firefly luciferase for normalization. Ionomycin treatment enhanced the relative luciferase activity (RLA), which was suppressed by calcineurin inhibitors. HEK293 cells that stably express human STIM1 and Orai1, components of the store-operated calcium entry (SOCE) machinery, gave a much higher RLA by stimulation with thapsigargin, an inhibitor of sarcoplasmic/endoplamic reticulum Ca²⁺-ATPase (SERCA). HEK293 cells deficient in a penta-EF-hand Ca²⁺-binding protein ALG-2 showed a higher RLA value than the parental cells by stimulation with an acetylcholine receptor agonist carbachol. The novel reporter gene system is found to be useful for applications to cell signaling research to monitor biological endpoint effects of cellular Ca²⁺ mobilization.

MiR-124 enhances cell radiosensitivity by targeting PDCD6 in nasopharyngeal carcinoma

BACKGROUND

Radiation resistance poses a major clinical challenge in treatment of nasopharyngeal carcinoma (NPC). Studies have shown that the abnormal expression of microRNAs (miRNAs) is associated with radiosensitivity, however, the mechanisms have not been fully elucidated. The aim of this study, therefore, was to investigate whether ectopic expression of miR-124 is correlated with radiosensitivity in NPC.

METHODS

In this study, the expression level of miR-124 was evaluated in NPC cell lines and patient specimens using quantitative reverse transcription-PCR (Real-time qPCR). Cell radiosensitivity was determined by colony formation assay. Target prediction algorithms and luciferase assay were used to confirm the target of miR-124. Tumor xenograft model was performed to understand the functions of miR-124 in vivo.

RESULTS

We found that miR-124 was down-regulated in both NPC specimens and NPC cell lines. Ectopic expression of miR-124 increased radiosensitivity of NPC cells. In vivo assays extended the significance of these results, showing that miR-124 overexpression decreased cell resistance to radiation treatment in tumor xenografts. Furthermore, we identified PDCD6 as a novel direct target of miR-124. Functional studies showed that knockdown PDCD6 enhanced cell radosensitivity to irradiation, and PDCD6 could rescue the effect caused by overexpression of miR-124, indicating that PDCD6 is a functional target of miR-124.

CONCLUSIONS

MiR-124 enhances cell radiosensitivity by targeting PDCD6, miR-124/PDCD6 axis may facilitate the development of novel targeted therapies for NPC.

MicroRNA-124-3p directly targets PDCD6 to inhibit metastasis in breast cancer

Breast cancer (BC) is the leading cause of cancer-associated mortality among women worldwide, with a poor 5-year survival rate, particularly among patients with metastatic BC. Previous studies have indicated that the dysregulation of microRNAs (miRNAs/miRs) is associated with carcinogenesis and metastasis. Thus, investigating the underlying molecular mechanisms by which miRNAs mediate their effects may aid in the improvement of BC treatment. In the present study, reverse transcription-quantitative polymerase chain reaction analyses were performed to investigate miR-124-3p expression in BC tissues. The expression of miR-124-3p was significantly decreased in primary BC tissues compared with that in adjacent non-tumor tissues. Downregulated miR-124-3p was correlated with lymph node metastasis and a low overall survival time. Wound-healing and Transwell assays revealed that MDA-MB-231 and MCF-7 cell motility was inhibited by miR-124-3p, but was promoted by a miR-124-3p inhibitor. Overexpression of miR-124-3p increased levels of E-cadherin, and decreased levels of N-cadherin and Vimentin, indicating that miR-124-3p inhibits the epithelial-mesenchymal transition. In addition, a bioinformatics analysis and subsequent in vitro experiments identified programmed cell death protein 6 (PDCD6) as a direct target of miR-124-3p. Restoration of PDCD6 expression impaired the metastasis inhibitor role of miR-124-3p by promoting cell invasion. Furthermore, the expression of miR-124-3p was inversely associated with PDCD6 mRNA levels in clinical breast tumors. Taken together, these data suggest that miR-124-3p inhibits tumor metastasis by inhibiting PDCD6 expression, and that the miR-124-3p/PDCD6 signaling axis may be a potential target for novel treatments in patients with advanced BC.

ALG2 regulates glioblastoma cell proliferation, migration and tumorigenicity

Apoptosis-linked gene-2 (ALG-2), also known as programmed cell death 6 (PDCD6), has recently been reported to be aberrantly expressed in various tumors and required for tumor cell viability. The aim of the present study was to investigate whether ALG-2 plays a crucial role in tumor cell proliferation, migration and tumorigenicity. In this study, we examined the expression of PDCD6 in glioblastoma cell lines and found that ALG-2 was generally expressed in glioblastoma cell lines. We also performed an analysis of an online database and found that high expression of ALG-2 was associated with poor prognosis (p = 0.039). We found that over-expression of ALG2 in glioblastoma could inhibit cell proliferation and, conversely, that down-regulation of ALG2 could promote cell proliferation. Further studies showed that over-expression of ALG2 inhibited the migration of tumor cells, whereas down-regulation of ALG2 promoted tumor cell migration. Finally, in vitro and in vivo studies showed that over-expression of ALG2 inhibited the tumorigenic ability of tumor cells, while down-regulation of ALG2 promoted tumor cell tumorigenic ability. In conclusion, ALG2 has a tumor suppressive role in glioblastoma and might be a potential target for the treatment of glioblastoma.

Multifaceted Roles of ALG-2 in Ca(2+)-Regulated Membrane Trafficking

ALG-2 (gene name: PDCD6) is a penta-EF-hand Ca²⁺-binding protein and interacts with a variety of proteins in a Ca²⁺-dependent fashion. ALG-2 recognizes different types of identified motifs in Pro-rich regions by using different hydrophobic pockets, but other unknown modes of binding are also used for non-Pro-rich proteins. Most ALG-2-interacting proteins associate directly or indirectly with the plasma membrane or organelle membranes involving the endosomal sorting complex required for transport (ESCRT) system, coat protein complex II (COPII)-dependent ER-to-Golgi vesicular transport, and signal transduction from membrane receptors to downstream players. Binding of ALG-2 to targets may induce conformational change of the proteins. The ALG-2 dimer may also function as a Ca²⁺-dependent adaptor to bridge different partners and connect the subnetwork of interacting proteins.