Tip60 modulates PLAGL2-mediated transactivation by acetylation

High Expression of PLAGL2 is Associated With Poor Prognosis in High-Grade Glioma

Pleomorphic adenoma gene like-2 (PLAGL2) has been implicated in the development and progression of diverse malignancies, including glioblastoma. An increasing number of studies have reported that dysregulated expression of PLAGL2 is a common phenomenon in different malignancies. However, the mechanism and biological functions of PLAGL2 in patients with high-grade glioma (HGG) remain unclear. In addition, the expression and clinical significance of PLAGL2 in HGG have not yet been reported. Herein, we investigated the expression patterns and prognostic values of PLAGL2 in patients with HGG by using various databases, including Tumor Immune Estimation Resource 2.0 (TIMER2.0), GENT2, ONCOMINE, GEPIA, Human Protein Atlas, and Gene Expression Omnibus datasets. In the present study, we analyzed the relationship between PLAGL2 mRNA expression and clinical parameters in 184 HGG cases and found that PLAGL2 presented positively high expression and was relevant to poor prognosis. Immunohistochemistry analysis confirmed the overexpression of PLAGL2 protein, which is mainly expressed in the nucleus of glioma. Additionally, a high level of expression of the PLAGL2 gene was associated with lower survival in progression-free survival and overall survival in GBM patients. The correlation analysis between PLAGL2 and immune infiltration related to the abundance of B cells, CD8⁺ T cells, CD4⁺ T cells, macrophages, DCs, and neutrophils was also performed using TIMER2.0. GSEA results showed that high PLAGL2 expression was associated with cell migration, proliferation, actin cytoskeletal, and angiogenesis. To sum up, our findings indicated that PLAGL2 could serve as an independent prognostic biomarker and might be a potential therapeutic target for HGG, which should be further investigated.

The PLAGL2/MYCN/miR-506-3p interplay regulates neuroblastoma cell fate and associates with neuroblastoma progression

Background

The oncogene MYCN is critical for tumorigenesis of several types of cancers including neuroblastoma. We previously reported that miR-506-3p repressed MYCN expression in neuroblastoma cells. However, the mechanism underlying such regulation was undetermined since there is no miR-506-3p target site in MYCN 3’UTR.

Methods

By a systematic investigation combining microarray, informatics and luciferase reporter assay, we identified that the transcriptional factor pleiomorphic adenoma gene-like 2 (PLAGL2) is a direct target of miR-506-3p that mediates its regulation on MYCN expression. Using CHIP-PCR and luciferase reporter assay, we validated the transcriptional regulation of MYCN by PLAGL2 and we further demonstrated the transcriptional regulation of PLAGL2 by MYCN. We examined the function of PLAGL2 in regulating neuroblastoma cell fate by cell viability assay, colony formation and Western blotting of differentiation markers. We examined the effect of retinoic acid, the differentiation agent used in neuroblastoma therapy, on miR-506-3p, PLAGL2 and MYCN expressions by quantitative PCR and Western blots. We investigated the clinical relevance of PLAGL2 expression by examining the correlation of tumor PLAGL2 mRNA levels with MYCN mRNA expression and patient survival using public neuroblastoma patient datasets.

Results

We found that miR-506-3p directly down-regulated PLAGL2 expression, and we validated a PLAGL2 binding site in the MYCN promoter region responsible for promoting MYCN transcription, thereby establishing a mechanism through which miR-506-3p regulates MYCN expression. Conversely, we discovered that MYCN regulated PLAGL2 transcription through five N-Myc-binding E-boxes in the PLAGL2 promoter region. We further confirmed the reciprocal regulation between endogenous PLAGL2 and MYCN in multiple neuroblastoma cell lines. Moreover, we found that PLAGL2 knockdown induced neuroblastoma cell differentiation and reduced cell proliferation, and combined knockdown of PLAGL2 and MYCN showed a synergistic effect. More strikingly, we found that high tumor PLAGL2 mRNA levels were significantly correlated with high MYCN mRNA levels and poor patient survival in neuroblastoma patients. Furthermore, we found that retinoic acid increased expression of miR-506-3p and repressed expression of MYCN and PLAGL2.

Conclusions

Our findings altogether suggest that the interplay network formed by PLAGL2, MYCN and miR-506-3p is an important mechanism in regulating neuroblastoma cell fate, determining neuroblastoma prognosis, and mediating the therapeutic function of retinoic acid.

Plag1 and Plagl2 have overlapping and distinct functions in telencephalic development

The Plag gene family has three members; Plagl1/Zac1, which is a tumor suppressor gene, and Plag1 and Plagl2, which are proto-oncogenes. All three genes are known to be expressed in embryonic neural progenitors, and Zac1 regulates proliferation, neuronal differentiation and migration in the developing neocortex. Here we examined the functions of Plag1 and Plagl2 in neocortical development. We first attempted, and were unable to generate, E12.5 Plag1;Plagl2 double mutants, indicating that at least one Plag1 or Plagl2 gene copy is required for embryonic survival. We therefore focused on single mutants, revealing a telencephalic patterning defect in E12.5 Plagl2 mutants and a proliferation/differentiation defect in Plag1 mutant neocortices. Specifically, the ventral pallium, a dorsal telencephalic territory, expands into the ventral telencephalon in Plagl2 mutants. In contrast, Plag1 mutants develop normal regional territories, but neocortical progenitors proliferate less and instead produce more neurons. Finally, in gain-of-function studies, both Plag1 and Plagl2 reduce neurogenesis and increase BrdU-uptake, indicative of enhanced proliferation, but while Plagl2 effects on proliferation are more immediate, Plag1 effects are delayed. Taken together, we found that the Plag proto-oncogenes genes are essential regulators of neocortical development and although Plag1 and Plagl2 functions are similar, they do not entirely overlap. This article has an associated First Person interview with the first author of the paper.

MYST-family histone acetyltransferases: beyond chromatin

Covalently modifying a protein has proven to be a powerful mechanism of functional regulation. N-epsilon acetylation of lysine residues was initially discovered on histones and has been studied extensively in the context of chromatin and DNA metabolism, such as transcription, replication and repair. However, recent research shows that acetylation is more widespread than initially thought and that it regulates various nuclear as well as cytoplasmic and mitochondrial processes. In this review, we present the multitude of non-histone proteins targeted by lysine acetyltransferases of the large and conserved MYST family, and known functional consequences of this acetylation. Substrates of MYST enzymes include factors involved in transcription, heterochromatin formation and cell cycle, DNA repair proteins, gluconeogenesis enzymes and finally subunits of MYST protein complexes themselves. Discovering novel substrates of MYST proteins is pivotal for the understanding of the diverse functions of these essential acetyltransferases in nuclear processes, signaling, stress response and metabolism.

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

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-alpha-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.