Saini, A. — Page 2 | bioRxiv Science

bioRxiv2020

Epigenetic Instability May Alter Cell State Transitions and Anticancer Drug Resistance

Drug resistance is a significant obstacle to successful and durable anti-cancer therapy. Targeted therapy is often effective during early phases of treatment; however, eventually cancer cells adapt and transition to drug-resistant cells states rendering the treatment ineffective. It is proposed that cell state can be a determinant of drug efficacy and manipulated to affect the development of anticancer drug resistance. In this work, we developed two stochastic cell state models - referenced to brain tumors - that included transcriptionally-permissive and -restrictive states based on the underlying hypothesis that epigenetic instability mitigates lock-in of drug-resistant states. One model used single-step state transitions, whereas the other considered a multi-step process to lock-in drug resistance. The latter model showed that with moderate epigenetic instability the drug-resistant cell populations were reduced, on average, by 60%, whereas a high level of epigenetic disruption reduced them by about 90%. Generation of epigenetic instability via epigenetic modifier therapy could be a viable strategy to mitigate anticancer drug resistance.

cancer biology↗

bioRxiv2019

The heme biosynthetic enzyme, 5-aminolevulinic acid synthase (ALAS), and GTPases in control of mitochondrial dynamics and ER contact sites, regulate heme mobilization to the nucleus.

Heme is an iron-containing cofactor and signaling molecule that is essential for much of aerobic life. All heme-dependent processes in eukaryotes require that heme is trafficked from its site of synthesis in the mitochondria to hemoproteins located throughout the cell. However, the mechanisms governing the mobilization of heme out of the mitochondria, and the spatio-temporal dynamics of these processes, are poorly understood. Herein, using genetically encoded fluorescent heme sensors, we developed a live cell assay to monitor heme distribution dynamics between the mitochondrial inner-membrane, where heme is synthesized, and the mitochondrial matrix, cytosol, and nucleus. We found that heme distribution occurs simultaneously via parallel pathways. In fact, surprisingly, we find that trafficking to the nucleus is [~]25% faster than to the cytosol or mitochondrial matrix. Moreover, we discovered that the heme biosynthetic enzyme, 5-aminolevulinic acid synthase (ALAS), and GTPases in control of the mitochondrial dynamics machinery, Mgm1 and Dnm1, and ER contact sites, Gem1, regulate the flow of heme between the mitochondria and nucleus. Altogether, our results indicate that the nucleus acquires heme faster than the cytosol or mitochondrial matrix, presumably for mitochondrial-nuclear retrograde signaling, and that GTPases that regulate mitochondrial dynamics and ER contact sites are hard-wired to cellular heme distribution systems.\n\nSummary StatementThe factors that govern the trafficking of heme, an essential but potentially cytotoxic cofactor and signaling molecule, are poorly understood. Herein, we developed a live-cell assay to monitor heme distribution kinetics and identified the first enzyme in the heme synthesis pathway and GTPases in control of mitochondrial-ER contact sites and dynamics as being critical modulators of heme trafficking.

cell biology↗