Interactome Analysis of Human Phospholipase D and Phosphatidic Acid-Associated Protein Network.

Mammalian phospholipase D (PLD) enzyme family consists of six members. Among them, PLD1/2/6 catalyzes phosphatidic acid (PA) production, while PLD3/4/5 has no catalytic activities. Deregulation of the PLD-PA lipid signaling has been associated with various human diseases including cancer. However, a comprehensive analysis of the regulators and effectors for this crucial lipid metabolic pathway has not been fully achieved. Using a proteomic approach, we defined the protein interaction network for the human PLD family of enzymes and PA and revealed diverse cellular signaling events involving them. Through it, we identified PJA2 as a novel E3 ubiquitin ligase for PLD1 involved in control of the PLD1-mediated mammalian target of rapamycin signaling. Additionally, we showed that PA interacted with and positively regulated sphingosine kinase 1. Taken together, our study not only generates a rich interactome resource for further characterizing the human PLD-PA lipid signaling but also connects this important metabolic pathway with numerous biological processes.

m6A demethylase FTO suppresses pancreatic cancer tumorigenesis by demethylating PJA2 and inhibiting Wnt signaling.

Pancreatic cancer is the deadliest malignancy of the digestive system and is the seventh most common cause of cancer-related deaths worldwide. The incidence and mortality of pancreatic cancer continue to increase, and its 5-year survival rate remains the lowest among all cancers. N6-methyladenine (m6A) is the most abundant reversible RNA modification in various eukaryotic messenger and long noncoding RNAs and plays crucial roles in the occurrence and development of cancers. However, the role of m6A in pancreatic cancer remains unclear. The present study aimed to explore the role of m6A and its regulators in pancreatic cancer and assess its underlying molecular mechanism associated with pancreatic cancer cell proliferation, invasion, and metastasis. Reduced expression of the m6A demethylase, fat mass and obesity-associated protein (FTO), was responsible for the high levels of m6A RNA modification in pancreatic cancer. Moreover, FTO demethylated the m6A modification of praja ring finger ubiquitin ligase 2 (PJA2), thereby reducing its mRNA decay, suppressing Wnt signaling, and ultimately restraining the proliferation, invasion, and metastasis of pancreatic cancer cells. Altogether, this study describes new, potential molecular therapeutic targets for pancreatic cancer that could pave the way to improve patient outcome.

ELK4 promotes the development of gastric cancer by inducing M2 polarization of macrophages through regulation of the KDM5A-PJA2-KSR1 axis.

BACKGROUND: We tried to elaborate the molecular mechanism of ETS-like transcription factor 4 (ELK4) affecting gastric cancer (GC) progression through M2 polarization of macrophages mediated by lysine-specific demethylase 5A (KDM5A)-Praja2 (PJA2)-kinase suppressor of ras 1 (KSR1) axis. METHODS: GC expression dataset was obtained from GEO database, and the downstream regulatory mechanism of ELK4 was predicted. Tumor-associated macrophages (TAMs) were isolated from GC tissues. The interaction among ELK4, KDM5A, PJA2 and KSR1 was analyzed by dual luciferase reporter gene, ChIP and Co-IP assays. The stability of KSR1 protein was detected by cycloheximide (CHX) treatment. After TAMs were co-cultured with HGC-27 cells, HGC-27 cell biological processes were assessed through gain- and loss-of function assays. Tumorigenicity was detected by tumorigenicity test in nude mice. RESULTS: In GC and TAMs, ELK4, KDM5A and KSR1 were highly expressed, while PJA2 was lowly expressed. M2 polarization of macrophages promoted the development of GC. ELK4 activated KDM5A by transcription and promoted macrophage M2 polarization. KDM5A inhibited the expression of PJA2 by removing H3K4me3 of PJA2 promoter, which promoted M2 polarization of macrophages. PJA2 reduced KSR1 by ubiquitination. ELK4 promoted the proliferative, migrative and invasive potentials of GC cells as well as the growth of GC xenografts by regulating KSR1. CONCLUSION: ELK4 may reduce the PJA2-dependent inhibition of KSR1 by transcriptional activation of KDM5A to promote M2 polarization of macrophages, thus promoting the development of GC.

Regulatory function of praja ring finger ubiquitin ligase 2 mediated by the P2rx3/P2rx7 axis in mouse hippocampal neuronal cells.

Praja2 (Pja2), a member of the growing family of mammalian RING E3 ubiquitin ligases, is reportedly involved in not only several types of cancer but also neurological diseases and disorders, but the genetic mechanism underlying the regulation of Pja2 in the nervous system remains unclear. To study the cellular and molecular functions of Pja2 in mouse hippocampal neuronal cells (MHNCs), we used gain- and loss-of-function manipulations of Pja2 in HT-22 cells and tested their regulatory effects on three Alzheimer's disease (AD) genes and cell proliferation. The results revealed that the expression of AD markers, including amyloid beta precursor protein (App), microtubule-associated protein tau (Mapt), and gamma-secretase activating protein (Gsap), could be inhibited by Pja2 overexpression and activated by Pja2 knockdown. In addition, HT-22 cell proliferation was enhanced by Pja2 upregulation and suppressed by its downregulation. We also evaluated and quantified the targets that responded to the enforced expression of Pja2 by RNA-Seq, and the results showed that purinergic receptor P2X, ligand-gated ion channel 3 and 7 (P2rx3 and P2rx7), which show different expression patterns in the critical calcium signaling pathway, mediated the regulatory effect of Pja2 in HT-22 cells. Functional studies indicated that Pja2 regulated HT-22 cells development and AD marker genes by inhibiting P2rx3 but promoting P2rx7, a gene downstream of P2rx3. In conclusion, our results provide new insights into the regulatory function of the Pja2 gene in MHNCs and thus underscore the potential relevance of this molecule to the pathophysiology of AD.

Identification of rare copy number variations reveals PJA2, APCS, SYNPO, and TAC1 as novel candidate genes in Autism Spectrum Disorders.

BACKGROUND: There is a strong evidence for genetic factors as the main causes of Autism Spectrum Disorders (ASD). To date, hundreds of genes have been identified either by copy number variations (CNVs) and/or single nucleotide variations. However, despite all the findings, the genetics of these disorders have not been totally explored. METHODS: Thus, the aim of our work was to identify rare CNVs and genes present in these regions in ASD children, using a high-resolution comparative genomic hybridization technique and quantitative PCR (qPCR) approach. RESULTS: Our results have shown 60-70 chromosomal aberrations per patient. We have initially selected 66 CNVs that have been further assessed using qPCR. Finally, we have validated 22 CNVs including 11 deletions and 11 duplications. Ten CNVs are de novo, 11 are inherited and one of unknown origin of transmission. Among the CNVs detected, novel ASD candidate genes PJA2, SYNPO, APCS, and TAC1 have been identified in our group of Lebanese patients. In addition, previously described CNVs have been identified containing genes such as SHANK3, MBP, CHL1, and others. CONCLUSION: Our study broadens the population spectrum of studied ASD patients and adds new candidates at the list of genes contributing to these disorders.

CD1d- and PJA2-related immune microenvironment differs between invasive breast carcinomas with and without a micropapillary feature.

BACKGROUND: Invasive micropapillary carcinoma (IMPC) of the breast is characterized by its unique morphology and frequent nodal metastasis. However, the mechanism for development of this unique subtype has not been clearly elucidated. The aim of this study was to obtain a better understanding of IMPC. METHODS: Using representative cases of mixed IMPC, mRNA expression in the micropapillary area and usual invasive area was compared. Then, immunohistochemical analyses for 294 cases (76 invasive carcinomas with a micropapillary feature [ICMF] and 218 invasive carcinomas without a micropapillary feature [ICNMF]) were conducted. Clinicopathological analyses were also studied. RESULTS: DNA microarray analyses for mixed IMPC showed that BC-1514 (C21orf118) was commonly upregulated in the micropapillary area. CAMK2N1, CD1d, PJA2, RPL5, SAMD13, TCF4, and TXNIP were commonly downregulated in the micropapillary area. Immunohistochemically, we confirmed that BC-1514 was more upregulated in ICMF than in ICNMF. CD1d and PJA2 were more downregulated in ICMF than ICNMF. All patients with cases of PJA2 overexpression survived without cancer recurrence during the follow-up period, although the differences for disease-free (p = 0.153) or overall survival (p = 0.272) were not significant. CONCLUSIONS: The CD1d- and PJA2-related tumour microenvironment might be crucial for IMPC. Further study of the immune microenvironment and micropapillary features is warranted.

Pja2 Inhibits Wnt/ß-catenin Signaling by Reducing the Level of TCF/LEF1.

Ubiquitination of proteins plays an essential role in various cellular processes, including protein degradation, DNA repair, and cell signaling pathways. Previous studies have shown that protein ubiquitination is implicated in regulating pluripotency as well as fate determination of stem cells. To identify how protein ubiquitination affects differentiation of embryonic stem cells, we analyzed microarray data, which are available in the public domain, of E3 ligases and deubiquitinases whose levels changed during stem cell differentiation. Expression of pja2, a member of the RING-type E3 ligase family, was up-regulated during differentiation of stem cells. Wnt/ß-catenin signaling is one of the most important signaling pathways for regulation of the self-renewal and differentiation of embryonic stem cells. Pja2 was shown to bind to TCF/LEF1, which are transcriptional factors for Wnt/ß-catenin signaling, and regulate protein levels by ubiquitination, leading to down-regulation of Wnt signaling activity. Based on these results, we suggest that E3 ligase Pja2 regulates stem cell differentiation by controlling the level of TCF/LEF1 by ubiquitination.

Pja2 Inhibits Wnt/β-catenin Signaling by Reducing the Level of TCF/LEF1

Ubiquitination of proteins plays an essential role in various cellular processes, including protein degradation, DNA repair, and cell signaling pathways. Previous studies have shown that protein ubiquitination is implicated in regulating pluripotency as well as fate determination of stem cells. To identify how protein ubiquitination affects differentiation of embryonic stem cells, we analyzed microarray data, which are available in the public domain, of E3 ligases and deubiquitinases whose levels changed during stem cell differentiation. Expression of pja2, a member of the RING-type E3 ligase family, was up-regulated during differentiation of stem cells. Wnt/β-catenin signaling is one of the most important signaling pathways for regulation of the self-renewal and differentiation of embryonic stem cells. Pja2 was shown to bind to TCF/LEF1, which are transcriptional factors for Wnt/β-catenin signaling, and regulate protein levels by ubiquitination, leading to down-regulation of Wnt signaling activity. Based on these results, we suggest that E3 ligase Pja2 regulates stem cell differentiation by controlling the level of TCF/LEF1 by ubiquitination.