Disease Progression In Lymphoma Research Articles

Abstract 259: Interplay between Bcl-2 and cFLIP in lymphoma disease progression is a function of an altered redox milieu

Abstract Bcl-2 is associated with chemoresistance and despite the preponderance of evidence linking its anti-apoptotic function to hematologic cancers, it’s now emerging that overexpression of Bcl-2 is a feature shared by a host of cancers. Canonically, the death inhibitory activity of Bcl-2 is associated with its ability to prevent mitochondrial outer membrane permeabilization. However, recent evidence has highlighted a novel facet in the biology of Bcl-2, whereby enforced expression of Bcl-2 resulted in an increase in mitochondrial oxygen consumption and elevated levels of the reactive oxygen species (ROS), superoxide (O2-.). Alleviating the levels of intracellular O2-. sensitized Bcl-2 overexpressing cells to death receptor induced apoptosis via a robust increase in upstream caspase 8 activation. Using a variety of functional mutants of the NOX-activating small GTPase Rac1, we show a clear link between Bcl-2 induced apoptosis resistance and intracellular O2-.. In the search for the molecular target of this inhibitory signal, we now show that Bcl-2 overexpression is associated with an increase in the transcription and protein levels of the receptor inhibitory protein, cFLIP. We employed pharmacological and genetic approaches to modulated intracellular O2-. and present evidence cFLIP is transcriptionally regulated by O2-.; increase in cFLIP promoter activity and mRNA levels. Interestingly, inhibiting glycolysis also resulted in downregulation of cFLIP in a ROS-dependent manner. Notably, primary cells derived from patients with lymphoma also showed a significant downregulation of cFLIP when subjected to conditions that decrease O2-. and elicited enhanced sensitivity to TRAIL-induced apoptosis. Importantly, TCGA and Affy meta-cohorts’ analyses revealed consistent correlation trend: Bcl-2 and cFLIP (CFLAR) were positively correlated; Bcl-2 and SOD1 (superoxide dismutase 1) were negatively correlated. A strong negative correlation was also observed between CFLAR and SOD1. Furthermore, Kaplan-Meier analyses of overall survival (OS) were performed in the in-house High expression of either Bcl-2 or CFLAR conferred poor OS outcome. When stratified by CFLAR and Bcl-2 expressions, cases with higher expression of the two genes had the worst prognosis with the shortest median survival. Notably, DLBCL with high Bcl-2 and low SOD1 had the worst OS outcome, compared against expression levels of Bcl-2 and SOD1. Together, these findings point to a concordance between cFLIP and Bcl-2, which negatively correlates with SOD1 in driving lymphoma progression. Citation Format: Jayshree L. Hirpara, Shazib Pervaiz. Interplay between Bcl-2 and cFLIP in lymphoma disease progression is a function of an altered redox milieu [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 259.

Epigenetic control via allosteric regulation of mammalian protein arginine methyltransferases

Arginine methylation on histones is a central player in epigenetics and in gene activation and repression. Protein arginine methyltransferase (PRMT) activity has been implicated in stem cell pluripotency, cancer metastasis, and tumorigenesis. The expression of one of the nine mammalian PRMTs, PRMT5, affects the levels of symmetric dimethylarginine (SDMA) at Arg-3 on histone H4, leading to the repression of genes which are related to disease progression in lymphoma and leukemia. Another PRMT, PRMT7, also affects SDMA levels at the same site despite its unique monomethylating activity and the lack of any evidence for PRMT7-catalyzed histone H4 Arg-3 methylation. We present evidence that PRMT7-mediated monomethylation of histone H4 Arg-17 regulates PRMT5 activity at Arg-3 in the same protein. We analyzed the kinetics of PRMT5 over a wide range of substrate concentrations. Significantly, we discovered that PRMT5 displays positive cooperativity in vitro, suggesting that this enzyme may be allosterically regulated in vivo as well. Most interestingly, monomethylation at Arg-17 in histone H4 not only raised the general activity of PRMT5 with this substrate, but also ameliorated the low activity of PRMT5 at low substrate concentrations. These kinetic studies suggest a biochemical explanation for the interplay between PRMT5- and PRMT7-mediated methylation of the same substrate at different residues and also suggest a general model for regulation of PRMTs. Elucidating the exact relationship between these two enzymes when they methylate two distinct sites of the same substrate may aid in developing therapeutics aimed at reducing PRMT5/7 activity in cancer and other diseases.