Biology subjects

Lev, A.

Publications and source records attributed to Lev, A..

4 recordsLinked to original sources

bioRxiv2021

Cap-independent translation and a precisely localized RNA sequence enable SARS-CoV-2 to control host translation and escape anti-viral response

Translation of SARS-CoV-2-encoded mRNAs by the host ribosomes is essential for its propagation. Following infection, the early expressed viral protein NSP1 binds the ribosome, represseses translation and induces mRNA degradation, while the host elicits anti-viral response. The mechanisms enabling viral mRNAs to escape this multifaceted repression remain obscure. Here we show that expression of NSP1 leads to destabilization of multi-exon cellular mRNAs, while intron-less transcripts, such as viral mRNAs and anti-viral interferon genes, remain relatively stable. We identified a conserved and precisely located cap-proximal RNA element devoid of guanosines that confers resistance to NSP1-meidated translation inhibition. Importantly, the primary sequence rather than the secondary structure is critical for protection. We further show that the genomic 5UTR of SARS-CoV-2 exhibits an IRES-like activity and promotes expression of NSP1 in an eIF4E-independent and Torin-1 resistant manner. Upon expression, NSP1 enhances cap-independent translation. However, the sub-genomic 5UTRs are highly sensitive to eIF4E availability, rendering viral propagation partially sensitive to Torin-1. The combined NSP1-mediated degradation of spliced mRNAs and translation inhibition of single-exon genes, along with the unique features present in the viral 5UTRs, ensure robust expression of viral mRNAs. These features can be exploited as potential therapeutic targets.

molecular biology↗

bioRxiv2021

A subset of CB002 xanthine analogues bypass p53-signaling to restore a p53 transcriptome and target an S-phase cell cycle checkpoint in tumors with mutated-p53

Mutations in TP53 occur commonly in the majority of human tumors and confer aggressive tumor phenotypes including metastasis and therapy resistance. CB002 and structural-analogues restore p53 signaling in tumors with mutant-p53 but we find that unlike other xanthines such as caffeine, pentoxifylline, and theophylline, they do not deregulate the G2-checkpoint. Novel CB002-analogues induce pro-apoptotic Noxa protein in an ATF3/4-dependent manner, whereas caffeine, pentoxifylline, and theophylline do not. By contrast to caffeine, CB002-analogues target an S-phase checkpoint associated with increased p-RPA/RPA2, p-ATR, decreased Cyclin A, p-histone H3 expression and downregulation of essential proteins in DNA-synthesis and -repair. CB002-analogue #4 enhances cell death, and decreases Ki-67 in patient-derived tumor-organoids without toxicity to normal human cells. Preliminary in vivo studies demonstrate anti-tumor efficacy in mice. Thus, a novel class of anti-cancer drugs show activation of p53 pathway signaling in tumors with mutated p53, and target an S-phase checkpoint.

cancer biology↗

bioRxiv2020

P53-independent restoration of p53 pathway in tumors with mutated p53 through ATF4 transcriptional modulation by ERK1/2 and CDK9

A long-term goal in the cancer-field has been to develop strategies for treating p53-mutated tumors. A novel small-molecule, PG3-Oc, restores p53 pathway-signaling in tumor cells with mutant-p53, independently of p53/p73. PG3-Oc partially upregulates the p53-transcriptome (13.7% of public p53 target-gene dataset; 15.2% of in-house dataset) and p53-proteome (18%, HT29; 16%, HCT116-p53-/-). Bioinformatic analysis indicates critical p53-effectors of growth-arrest (p21), apoptosis (PUMA, DR5, Noxa), autophagy (DRAM1), and metastasis-suppression (NDRG1) are induced by PG3-Oc. ERK1/2- and CDK9-kinases are required to upregulate ATF4 by PG3-Oc which restores p53 transcriptomic-targets in cells without functional-p53. PG3-Oc represses MYC (ATF4-independent), and upregulates PUMA (ATF4-dependent) in mediating cell death. With largely nonoverlapping transcriptomes, induced-ATF4 restores p53 transcriptomic targets in drug-treated cells including functionally important mediators such as PUMA and DR5. Our results demonstrate novel p53-independent drug-induced molecular reprogramming involving ERK1/2, CDK9, and ATF4 to restore upregulation of p53 effector genes required for cell death and tumor suppression.

cancer biology↗

bioRxiv2020

HIF1α inhibition by dual targeting of CDK4/6 and HSP90 reduces cancer cell viability including Rb-deficient cells

Most cancers harbor intra-tumoral hypoxia which promotes tumor progression and therapy resistance. Hypoxia-inducible factor 1 (HIF1) mediates an adaptive response to hypoxia and contributes to multiple cancer hallmarks. We describe cancer therapeutic targeting of HIF1 by combination of CDK4/6 inhibitors (CDK4/6i) and heat-shock protein 90 inhibitors (HSP90i). CDK1 contributes to HSP90-mediated HIF1 stabilization whereas CDK1-knockdown enhances HIF1 reduction by HSP90i. Dual CDK1- and HSP90-inhibition increases apoptosis and synergistically inhibits cancer cell viability. To translate our findings, we use FDA-approved CDK4/6i in combination with HSP90i to reduce HIF1 expression and suppress viability of multiple cancer cell types, including Rb-deficient cancer cells. Overexpression of HIF1668E partially rescues the cell viability inhibition by combination CDK4/6i and HSP90i treatment under hypoxia. CDK4/6i and HSP90i suppresses tumor growth in vivo. Thus, combined targeting of CDK4/6 and HSP90, through a drug class effect, inhibits HIF1 and shows preclinical anti-cancer therapeutic efficacy, including with Rb-deficiency.

cancer biology↗