Côté (2012) Alternatively spliced protein arginine methyltransferase 1 isoform PRMT1v2 promotes the survival and invasiveness of breast cancer cells, Cell Cycle, 11:24,[4597][4598][4599][4600][4601][4602][4603][4604][4605][4606][4607][4608][4609][4610][4611][4612]

Breast cancer is the most commonly diagnosed female cancer in the world. Though therapeutic treatments are available to treat breast cancer and in some instances are successful, the occurrence of unsuccessful treatment, or the rate of tumour recurrence, still remains strikingly high. Therefore, novel therapeutic treatment targets need to be discovered and tested. The protein arginine methyltransferases (PRMTs) are a family of enzymes that catalyse arginine methylation and are implicated in a myriad of cellular pathways including transcription, DNA repair, RNA metabolism, signal transduction, protein-protein interactions and subcellular localisation. In breast cancer, the expression levels and enzymatic activity of a number of PRMTs is dysregulated; significantly altering the regulation of many cellular pathways that are implicated in breast cancer development and progression. Here, we review the current knowledge on PRMTs in breast cancer and provide a rationale for how PRMTs may provide novel therapeutic targets for the treatment of breast cancer.

Protein arginine methyltransferases (PRMTs) are a family of enzymes that modify proteins by methylating the guanidino nitrogen atoms of arginine residues to regulate cellular processes such as chromatin remodeling, pre-mRNA splicing, and signal transduction. PRMT7 is the single type III PRMT solely capable of arginine monomethylation. To date, other than histone proteins, there are very few identified substrates of PRMT7. We therefore performed quantitative mass spectrometry experiments to identify PRMT7’s interactome and potential substrates to better characterize the enzyme’s biological function(s) in cells. These experiments revealed that PRMT7 interacts with and can methylate eukaryotic translation initiation factor 2 alpha (eIF2α), in vitro and in breast cancer cells. Furthermore, we uncovered a potential regulatory interplay between eIF2α arginine methylation by PRMT7 and stress-induced phosphorylation status of eIF2α at serine 51. Finally, we demonstrated that PRMT7 is required for eIF2α-dependent stress granule formation in the face of various cellular stresses. Altogether, our findings implicate PRMT7 as a novel mediator of eIF2α-dependent cellular stress response pathways.

Eukaryotic cells form stress granules under a variety of stresses, however the signaling pathways regulating their formation remain largely unknown. We have determined that the Saccharomyces cerevisiae lysine acetyltransferase complex NuA4 is required for stress granule formation upon glucose deprivation but not heat stress. Further, the Tip60 complex, the human homolog of the NuA4 complex, is required for stress granule formation in cancer cell lines. Surprisingly, the impact of NuA4 on glucose-deprived stress granule formation is partially mediated through regulation of acetyl-CoA levels, which are elevated in NuA4 mutants. While elevated acetyl-CoA levels suppress the formation of glucose-deprived stress granules, decreased acetyl-CoA levels enhance stress granule formation upon glucose deprivation. Further our work suggests that NuA4 regulates acetyl-CoA levels through the Acetyl-CoA carboxylase Acc1. Altogether this work establishes both NuA4 and the metabolite acetyl-CoA as critical signaling pathways regulating the formation of glucose-deprived stress granules.

BackgroundHepatocellular carcinoma (HCC), one of the most common cancers world-wide occurs twice as often in men compared to women. Predisposing conditions such as alcoholism, chronic viral hepatitis, aflatoxin B1 ingestion, and cirrhosis all contribute to the development of HCC.MethodsWe used a combination of methylation specific PCR and bisulfite sequencing, qReal-Time PCR (qPCR), and Western blot analysis to examine epigenetic changes for the Polo-like kinases (Plks) during the development of hepatocellular carcinoma (HCC) in Plk4 heterozygous mice and murine embryonic fibroblasts (MEFs).ResultsHere we report that the promoter methylation of Plk4 CpG islands increases with age, was more prevalent in males and that Plk4 epigenetic modification and subsequent downregulation of expression was associated with the development of HCC in Plk4 mutant mice. Interestingly, the opposite occurs with another Plk family member, Plk1 which was typically hypermethylated in normal liver tissue but became hypomethylated and upregulated in liver tumours. Furthermore, upon alcohol exposure murine embryonic fibroblasts exhibited increased Plk4 hypermethylation and downregulation along with increased centrosome numbers and multinucleation.ConclusionsThese results suggest that aberrant Plk methylation is correlated with the development of HCC in mice.

Tudor domain containing protein 3 (TDRD3) is a modular protein identified based on its ability to recognize methylated arginine motifs through its Tudor domain. We have previously shown that TDRD3 localizes to cytoplasmic stress granules, a structure shown to promote survival upon treatment with chemotherapeutic drugs in cancer cells. Here, we report TDRD3 as a novel regulator of cell proliferation and invasion in breast cancer cells. Our study also demonstrates that TDRD3 depletion inhibits tumor formation and metastasis to the lung in vivo. Furthermore, we show that TDRD3 regulates the expression of a number of key genes associated with promotion of breast cancer tumorigenesis and disease progression. Strikingly, we report that TDRD3 regulates some of these key targets at the level of translation. These findings provide the first experimental demonstration of a functional role for TDRD3 in promoting breast cancer development and progression, and identify TDRD3 as a potential new therapeutic target for breast cancer.

Background: The polo-like kinases (Plks) are a group of serine/threonine kinases which have roles in many aspects of cellular function including the regulation of mitotic activity and cellular stress responses. This study focuses on Plk4, the most divergent member of the Plk family, which is necessary for proper cellular proliferation. More specifically, alterations in Plk4 levels cause significantly adverse mitotic defects including abnormal centrosome duplication and aberrant mitotic spindle formation. We sought to clarify the effect of reduced Plk4 levels on the cell by examining transcript profiles of Plk4 wild-type and heterozygous mouse embryonic fibroblasts (MEFs). Subsequently, the levels of several key proteins involved in the DNA damage response were examined.

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