A Golgi-specific protein PAQR3 is closely associated with the progression, metastasis and prognosis of human gastric cancers

PAQR3 modulates H3K4 trimethylation by spatial modulation of the regulatory subunits of COMPASS-like complexes in mammalian cells

Histone modification plays important roles in many biological processes such as development and carcinogenesis. Methylation of histone H3 lysine 4 (H3K4) is commonly associated with transcriptional activation of genes. H3K4 methylation in mammalian cells is carried out by COMPASS (complex of proteins associated with Set1)-like complexes that are composed of catalytic subunits such as MLL1 (mixed-lineage leukaemia 1) and multiple regulatory subunits in which WDR5 (WD40 repeat-containing protein 5), RBBP5 (retinoblastoma-binding protein 5), ASH2 (absent, small or homoeotic discs 2) and DPY30 [constituting the WRAD sub-complex (WDR5-ASH2-RBBP5-DPY30 complex)] are the major ones shared from yeast to metazoans. We report, in the present paper, a new mode of spatial regulation of H3K4 methyltransferase complexes. PAQR3 (progestin and adipoQ receptors member 3), a tumour suppressor specifically localized in the Golgi apparatus, negatively regulates H3K4 trimethylation (H3K4me3) in mammalian cells. Consistently, HOXC8 and HOXA9 gene expression was negatively regulated by PAQR3 expression levels. Hypoxia-induced H3K4me3 was augmented by PAQR3 knockdown and suppressed by PAQR3 overexpression in AGS gastric cancer cells. PAQR3 was able to interact directly or indirectly with the four members of the WRAD sub-complex and tether them to the Golgi apparatus, accompanied by reduction in histone methyltransferase activity in the nucleus. PAQR3 also interfered with the interaction of WDR5 with the C-terminus of MLL1 (C-ter). Collectively, our study indicates that PAQR3 negatively modulates H3K4 methylation via altering the subcellular compartmentalization of the core regulatory subunits of the COMPASS-like complexes in mammalian cells.

DDB2 is involved in ubiquitination and degradation of PAQR3 and regulates tumorigenesis of gastric cancer cells

DDB2 (damage-specific DNA-binding protein 2) is the product of the xeroderma pigmentosum group E gene which is involved in the initiation of nucleotide excision repair via an ubiquitin ligase complex together with DDB1 and CUL4A (cullin 4A). PAQR3 (progestin and adipoQ receptor family member III) is a newly discovered tumour suppressor that is implicated in the development of many types of human cancers. In the present paper, we report that DDB2 is involved in ubiquitination and degradation of PAQR3. DDB2 is able to interact with PAQR3 in vivo and in vitro. Both overexpression and knockdown experiments reveal that the protein expression level, protein stability and polyubiquitination of PAQR3 are changed by DDB2. Negative regulation of EGF (epidermal growth factor)- and insulin-induced signalling by PAQR3 is also altered by DDB2. At the molecular level, Lys(61) of PAQR3 is targeted by DDB2 for ubiquitination. The cell proliferation rate and migration of gastric cancer cells are inhibited by DDB2 knockdown and such effects are abrogated by PAQR3 knockdown, indicating that the effect of DDB2 on the cancer cells is mediated by PAQR3. Collectively, our studies not only pinpoint that DDB2 is a post-translational regulator of PAQR3, but also indicate that DDB2 may play an active role in tumorigenesis via regulating PAQR3.

Pim-1 acts as an oncogene in human salivary gland adenoid cystic carcinoma

Background

Pim-1 (Provirus integration site for Moloney murine leukemia virus 1) belongs to the Ser/Thr kinase family and plays a pivotal role in occurrence and development of oncogenesis. Recent studies have demonstrated that Pim-1 phosphorylates RUNX3 and alters its subcellular localization. However, few studies have concerned the implications of Pim-1 in the salivary gland adenoid cystic carcinoma (ACC). In this study, we aimed to clarify the function of Pim-1 in ACC in vitro. Meanwhile, we measured the levels of Pim-1 and RUNX3 in the ACC tissues. The correlations between Pim-1/RUNX3 levels and clinical parameters were also analyzed.

Methods

SACC-83 and SACC-LM cells were transfected with the Pim-1 siRNA. Pim-1 mRNA and protein expression were measured using real-time PCR and immnuoblot, respectively. Cell proliferation was analyzed by CCK-8 assay. Cell cycle, apoptosis, and mitochondrial membrane potential were detected by flow cytometry. Effects of Pim-1 on cells’ invasion were evaluated by transwell migration assay. Pim-1 and RUNX3 levels in ACC tissues were examined by immunohistochemistry.

Results

Pim-1 siRNA reduces cell proliferation, induces apoptosis, causes cell cycle arrest through cell cycle related proteins (Cyclin D1 and CDK4), mitochondrial depolarization, and decreases invasive ability in SACC-83 and SACC-LM cells. Pim-1 and RUNX3 levels are significantly relevant and associated with T-stage and nerve invasion in the ACC tissues.

Conclusions

This study demonstrates the oncogenic role of Pim-1 in ACC. The findings also suggest that Pim-1 may serve as a neoteric therapeutic target and potential prognostic marker for ACC cancer.