Byrum, S. | Search bioRxiv

bioRxiv2020

YY1 cistrome analysis uncovers an essential requirement of the YY1:BRD4-PFKP regulatory axis for promoting tumorigenesis of castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) is a terminal disease, demanding a better understanding of its pathogenesis. Targeted therapy needs to be developed for CRPC due to its heterogeneity and resistance to current treatments. Here, through cistrome study of YY1, a transcription factor significantly overexpressed during prostate cancer progression, we identify a YY1-PFKP axis to be essential for CRPC tumorigenesis. Depletion of YY1 in independent CRPC models dramatically reduced tumor cell growth in vitro and delayed oncogenic progression in vivo. Importantly, YY1 functions as a master regulator of prostate tumor metabolism including the Warburg effect and mitochondria respiration. Loss-of-function and rescue studies further reveals a mechanistic underpinning in which YY1 directly binds and trans-activates PFKP, a gene encoding the rate-limiting enzyme for glycolysis, significantly contributing to the YY1-enforced oncogenic phenotypes such as enhanced tumor cell glycolysis and malignant growth. Additionally, a vast majority of gene-regulatory element in advanced prostate cancer cells are bound by YY1, lending a support for its role as a master regulator of prostate cancer progression. YY1 interactome studies point to bromodomain-containing coactivators in prostate cancer, which act as functional partners of YY1 to potentiate YY1-related target gene activation. Altogether, this study unveils an unexplored YY1:BRD4-PFKP oncogenic axis operating in advanced prostate cancer with implications for therapy.

cancer biology↗

bioRxiv2020

Methionine stress induces ferroptosis in methionine dependent cancer cells

Dietary methionine restriction is associated with a reduction in tumor growth in preclinical studies and an increase in lifespan in animal models. The mechanism by which methionine restriction inhibits tumor growth while sparing normal cells is incompletely understood, except for the observation that normal cells can utilize methionine or homocysteine interchangeably (methionine independence) while most cancer cells are strictly dependent on methionine availability. Here, we compared a typical methionine dependent and a rare methionine independent melanoma cell line. We found that replacing methionine with homocysteine generally induced hypomethylation in gene promoters. We isolated nuclear proteins and submitted it for tandem mass tag (TMT) proteomics. This analysis revealed that several proteins involved in the mitochondrial integrated stress response (ISR) were upregulated in response to the replacement of methionine to homocysteine in both cell lines, but to a much greater degree in the methionine dependent cell line. Consistent with the ISR signature, a proteomic analysis of a subcellular fraction enriched for mitochondrial content revealed a strong enrichment for proteins involved in oxidative phosphorylation. Analysis of cellular bioenergetics confirmed that homocysteine induces a decrease in ATP production from oxidative phosphorylation and glycolysis, but to a similar extent in methionine dependent and methionine independent cells. The mitochondrial integrated stress response shared a signature with ferroptosis. Methionine dependent cells displayed a strong ferroptotic signature, which was decreased by half in methionine independent cells. Consistent with ferroptosis, lipid peroxidation was significantly increased in methionine independent cells grown in homocysteine, and viability could be rescued partially but significantly with the inhibitor ferrostatin. Therefore, we propose that methionine stress induces ferroptotic cell death in methionine dependent cancer cells.

cancer biology↗