The overexpression of PRMT5 is highly correlated to poor clinical outcomes for colorectal cancer (CRC) patients. Importantly, our previous work demonstrated that PRMT5 overexpression could substantially augment activation of the nuclear factor kappa B (NF-κB) via methylation of arginine 30 (R30) on its p65 subunit, while knockdown of PRMT5 showed the opposite effect. However, the precise mechanisms governing this PRMT5/NF-κB axis are still largely unknown. Here, we report a novel finding that PRMT5 is phosphorylated on serine 15 (S15) in response to interleukin-1β (IL-1β) stimulation. Interestingly, we identified for the first time that the oncogenic kinase, PKCι could catalyze this phosphorylation event. Overexpression of the serine-to-alanine mutant of PRMT5 (S15A), in either HEK293 cells or CRC cells HT29, DLD1, and HCT116 attenuated NF-κB transactivation compared to WT-PRMT5, confirming that S15 phosphorylation is critical for the activation of NF-κB by PRMT5. Furthermore, the S15A mutant when compared to WT-PRMT5, could downregulate a subset of IL-1β-inducible NF-κB-target genes which correlated with attenuated promoter occupancy of p65 at its target genes. Additionally, the S15A mutant reduced IL-1β-induced methyltransferase activity of PRMT5 and disrupted the interaction of PRMT5 with p65. Furthermore, our data indicate that blockade of PKCι-regulated PRMT5-mediated activation of NF-κB was likely through phosphorylation of PRMT5 at S15. Finally, inhibition of PKCι or overexpression of the S15A mutant attenuated the growth, migratory, and colony-forming abilities of CRC cells compared to the WT-PRMT5. Collectively, we have identified a novel PKCι/PRMT5/NF-κB signaling axis, suggesting that pharmacological disruption of this pivotal axis could serve as the basis for new anti-cancer therapeutics.

The proinflammatory transcription factor nuclear factor-κB (NF-κB) has emerged as a central player in inflammatory responses and tumor development since its discovery three decades ago. In general, aberrant NF-κB activity plays a critical role in tumorigenesis and acquired resistance to chemotherapy. This aberrant NF-κB activity frequently involves several post-translational modifications of NF-κB, including phosphorylation. In this chapter, we will specifically cover the phosphorylation sites reported on the p65 subunit of NF-κB and their relationship to cancer. Importantly, phosphorylation is catalyzed by different kinases using adenosine triphosphate (ATP) as the phosphorus donor. These kinases are frequently hyperactive in cancers and thus may serve as potential therapeutic targets to treat different cancers.

Colorectal cancer (CRC) is one of the most aggressive cancers worldwide and is known to develop through a stepwise process involving the accumulation of several genetic and epigenetic alterations. Furthermore, numerous studies have highlighted the significant role that certain epigenetic enzymes play in CRC pathogenesis, particularly those that govern chromatin components in the promoter regions of tumor suppressors and oncogenes. Here, we delineate the relationship between CRC-associated epigenetic marks, their modifying enzymes, and the classification of CRC into distinct molecular pathways or subtypes. Moreover, we discuss some of the most prominent methyltransferases, demethylases, acetyltransferases, and deacetylases, which have been targeted for preclinical and clinical CRC treatment. Notably, inhibitors against these epigenetic enzymes are a promising new class of anticancer drugs, with several obtaining Food and Drug Administration (FDA) approval for the treatment of blood and solid tumors. By highlighting the epigenetic molecular pathways leading to CRC development as well as providing an update on current CRC epigenetic therapies, this chapter sheds fresh insight into new and emerging avenues for future therapeutics.