Modulation of PLAGL2 transactivation by positive cofactor 2 (PC2), a component of the ARC/Mediator complex

Department of Veterinary Molecular Biology, Montana State University, Bozeman, MT 59717, USA
Gene (Impact Factor: 2.08). 02/2010; DOI: 10.1016/j.gene.2009.12.003

ABSTRACT The pleomorphic adenoma gene (PLAG) family of transcription factors regulates a wide range of physiological processes, including cell proliferation, tissue-specific gene regulation, and embryonic development, although little is known regarding the mechanisms that regulate PLAG protein activity. In this study, a yeast two-hybrid screen identified PC2, a component of the Mediator complex, as a PLAGL2-binding protein. We show that PC2 cooperates with PLAGL2 and PU.1 to enhance the activity of a known PLAGL2 target promoter (NCF2). The PLAGL2-binding element in the NCF2 promoter consisted of the core sequence of the bipartite PLAG1 consensus site, but lacked the G-cluster motif, and was recognized by PLAGL2 zinc fingers 5 and 6. Promoter and PLAGL2 mutants showed that PLAGL2 and PU.1 were required to bind to their respective sites in the promoter, and PC2 knockdown demonstrated that PC2 was essential for enhanced promoter activity. Co-immunoprecipitation and promoter-reporter studies reveal that the effect of PC2 on PLAGL2 target promoter activity was conferred via the C-terminus of PLAGL2, the region that is required for PC2 binding and contains the PLAGL2 activation domain. Importantly, chromatin immunoprecipitation analysis and PC2 knockdown studies confirmed that endogenous PC2 protein associated with the NCF2 promoter in MM1 cells in the region occupied by PLAGL2, and was required for PLAGL2 target promoter activity in TNF-α-treated MM1 cells, respectively. Lastly, the expression of another known PLAGL2 target gene, insulin-like growth factor II (IGF-II), was greatly diminished in the presence of PC2 siRNA. Together, the data identify PC2 as a novel PLAGL2-binding protein and important mediator of PLAGL2 transactivation.

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    ABSTRACT: Numerous previous studies have revealed that pleomorphic adenoma gene-like 2 (PLAGL2) is a transcription factor that is active in cancer progression. The aim of this study was to investigate the role of PLAGL2 in the development, progression and prognosis of gastrointestinal cancer. Immunohistochemical analysis revealed that PLAGL2 was expressed in gastrointestinal tumors and adjacent normal tissues. The expression of PLAGL2 was significantly higher in 225 colorectal cancer tissues than in 66 adjacent non-tumor tissues (P = 0.037). However, expression was not significantly different between 286 gastric tumors and 57 adjacent non-tumor tissues (P = 0.352). Moreover, the PLAGL2 expression level significantly correlated with the depth of tumor invasion in colorectal cancer (P = 0.030). However, the PLAGL2 expression level significantly correlated with tumor size in gastric cancer (P = 0.046). Furthermore, we performed survival analyses and found that neither higher nor lower PLAGL2 expression was a prognostic factor in gastrointestinal cancer. Our findings indicate that PALGL2 serves as a tumor oncoprotein in the development and progression of colorectal cancer. However, the role of this protein in the development, progression and prognosis of gastric cancer is uncertain. Further investigation into the molecular mechanisms of PLAGL2 activity in gastrointestinal cancer is warranted.
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    ABSTRACT: The proto-oncogene, pleomorphic adenoma gene-like 2 (PLAGL2), is implicated in a variety of cancers including acute myeloid leukemia (AML), malignant glioma, colon cancer, and lung adenocarcinoma. There is additional evidence that PLAGL2 can function as a tumor suppressor by initiating cell cycle arrest and apoptosis. Interestingly, PLAGL2 has also been implicated in human myelodysplastic syndrome, a disease that is characterized by ineffective hematopoiesis and can lead to fatal cytopenias (low blood counts) as a result of increased apoptosis in the marrow, or, in about one-third of cases, can progress to AML. To gain a better understanding of the actions of PLAGL2 in human myeloid cells, we generated a stable PLAGL2-inducible cell line, using human promonocytic U937 cells. PLAGL2 expression inhibited cell proliferation which correlated with an accumulation of cells in G1, apoptotic DNA-laddering, an increase in caspase 3, 8, and 9 activity, and a loss of mitochondrial transmembrane potential. There was significant increase in the p53 homologue, p73, with PLAGL2 expression, and consistent with mechanisms of p73-regulated cell cycle control and apoptosis, there was increased expression of known p73 target genes p21, DR5, TRAIL, and Bax. PLAGL2-induced cell cycle block was abolished in the presence of p73 siRNA. Together, these data support a role for PLAGL2 in cell cycle regulation and apoptosis via activation of p73.
    Apoptosis 11/2011; 17(3):236-47. DOI:10.1007/s10495-011-0672-3 · 3.61 Impact Factor


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May 26, 2014