Glutathionylation Decreases Methyltransferase Activity of PRMT5 and Inhibits Cell Proliferation

Extracellular vesicles from colorectal cancer cells promote metastasis via the NOD1 signalling pathway

Pattern-recognition receptors (PRRs) have been shown to promote tumour metastasis via sensing tumour cell-derived small extracellular vesicles (EVs). Nucleotide-binding oligomerisation domain 1 (NOD1), a cytoplasmic PRR, plays a role in colorectal cancer (CRC) by detecting bacterial products. However, the precise mechanisms underlying the effects of NOD1, following identification of CRC cell-derived EVs (CRC-EVs), to potentiate CRC liver metastasis (CRC-LM), remain poorly understood. Here, we demonstrate that CRC-EVs activate NOD1 in macrophages to initiate secretion of inflammatory cytokines and chemokines. NOD1-activated macrophages also promote CRC cell migration, while in a murine model of liver metastasis (LM), NOD1-deficient mice exhibit reduced metastasis following CRC-EV treatment. Furthermore, cell division cycle 42 (CDC42), a small Rho guanosine-5'-triphosphate (GTP)ase, is delivered by CRC-EVs into macrophages where it activates NOD1. In addition, EVs from the plasma of patients with CRC-LM mediate NOD1 activation in human peripheral blood mononuclear cells. Moreover, high NOD1 expression in tumour tissues is associated with poor prognosis of CRC-LM. Our findings suggest that CRC-EVs activate NOD1 to promote tumour metastasis, thus, NOD1 may serve as a potential target in the diagnosis and treatment of CRC-LM.

PRMT5 regulates ATF4 transcript splicing and oxidative stress response

Protein methyltransferase 5 (PRMT5) symmetrically dimethylates arginine residues leading to regulation of transcription and splicing programs. Although PRMT5 has emerged as an attractive oncology target, the molecular determinants of PRMT5 dependency in cancer remain incompletely understood. Our transcriptomic analysis identified PRMT5 regulation of the activating transcription factor 4 (ATF4) pathway in acute myelogenous leukemia (AML). PRMT5 inhibition resulted in the expression of unstable, intron-retaining ATF4 mRNA that is detained in the nucleus. Concurrently, the decrease in the spliced cytoplasmic transcript of ATF4 led to lower levels of ATF4 protein and downregulation of ATF4 target genes. Upon loss of functional PRMT5, cells with low ATF4 displayed increased oxidative stress, growth arrest, and cellular senescence. Interestingly, leukemia cells with EVI1 oncogene overexpression demonstrated dependence on PRMT5 function. EVI1 and ATF4 regulated gene signatures were inversely correlated. We show that EVI1-high AML cells have reduced ATF4 levels, elevated baseline reactive oxygen species and increased sensitivity to PRMT5 inhibition. Thus, EVI1-high cells demonstrate dependence on PRMT5 function and regulation of oxidative stress response. Overall, our findings identify the PRMT5-ATF4 axis to be safeguarding the cellular redox balance that is especially important in high oxidative stress states, such as those that occur with EVI1 overexpression.

Protein Arginine Methyltransferase 5 Functions via Interacting Proteins

The protein arginine methyltransferases (PRMTs) are involved in such biological processes as transcription regulation, DNA repair, RNA splicing, and signal transduction, etc. In this study, we mainly focused on PRMT5, a member of the type II PRMTs, which functions mainly alongside other interacting proteins. PRMT5 has been shown to be overexpressed in a wide variety of cancers and other diseases, and is involved in the regulation of Epstein-Barr virus infection, viral carcinogenesis, spliceosome, hepatitis B, cell cycles, and various signaling pathways. We analyzed the regulatory roles of PRMT5 and interacting proteins in various biological processes above-mentioned, to elucidate for the first time the interaction between PRMT5 and its interacting proteins. This systemic analysis will enrich the biological theory and contribute to the development of novel therapies.