Biology subjects

Sami, A.

Publications and source records attributed to Sami, A..

3 recordsLinked to original sources

bioRxiv2025

APOBEC3A-Induced DNA Damage Drives Polymerase Theta Dependency and Synthetic Lethality in Cancer

APOBEC3 cytidine deaminases drive cancer evolution. There is an unmet need to target cancer cells with APOBEC3 activity. Here, we identify error-prone theta-mediated end joining (TMEJ) as the main pathway for repairing APOBEC3-induced double-strand breaks (DSBs). Using fluorescent DSB repair reporters and a novel biochemical assay, we demonstrate that APOBEC3A competes with replication protein A (RPA) for single-stranded DNA overhangs, exposing microhomologous sequences to shift DSB repair towards error-prone TMEJ. Genomic analysis of clinical tumor samples confirmed the co-occurrence and proximity between APOBEC3-induced mutational footprints, microhomology-mediated deletions (MMDs), and TMEJ-associated chromosomal instability signatures. Crucially, inhibition of DNA polymerase theta (Pol{theta}) synergizes with APOBEC3A-induced DSBs to induce synthetic lethality in vitro and in vivo. Collectively, our findings identify TMEJ as the preferred mechanism for repairing APOBEC3A-induced DSBs and establish Pol{theta} inhibition as a novel promising strategy to eliminate cancer cells with APOBEC3A activity.

cancer biology↗

bioRxiv2024

Uncovering Porphyrin Accumulation in the Tumor Microenvironment

Heme, an iron-containing tetrapyrrole, is essential in almost all organisms. Heme biosynthesis needs to be exquisitely regulated particularly given the potential cytotoxicity of protoporphyrin IX, the intermediate preceding heme formation. Here, we report on the porphyrin intermediate accumulation within the tumor microenvironment (TME), which we propose to result from dysregulation of heme biosynthesis concomitant with an enhanced cancer survival dependence on mid-step genes, a process we recently termed Porphyrin Overdrive. Specifically, porphyrins build up in both lung cancer cells and stromal cells in the TME. Within the TMEs stromal cells, evidence supports cancer-associated fibroblasts (CAFs) actively producing porphyrins through an imbalanced pathway. Conversely, normal tissues exhibit no porphyrin accumulation, and CAFs deprived of tumor cease porphyrin overproduction, indicating that both cancer and tumor-stromal porphyrin overproduction is confined to the cancer-specific tissue niche. The clinical relevance of our findings is implied by establishing a correlation between imbalanced porphyrin production and overall poorer survival in more aggressive cancers. These findings illuminate the anomalous porphyrin dynamics specifically within the tumor microenvironment, suggesting a potential target for therapeutic intervention.

cancer biology↗

bioRxiv2023

Widespread readthrough events in plants reveal unprecedented plasticity of stop codons

Stop codon readthrough (SCR), the decoding of a stop codon as a sense codon by the ribosome, has important biological implications but remains largely uncharacterized in plants. Here, we identified 1,009 SCR events in two monocots (maize, rice) and two dicots (soybean, Arabidopsis) using a proteogenomic strategy with 80 customized databases. SCR transcripts were mostly significantly shorter and had fewer components than non-SCR transcripts in two monocot plants, although these differences were not as significant in the dicots. Mass spectrometry evidence revealed that all three stop codons involved in SCR events could be recoded as 20 standard amino acids, some of which were also supported by suppressor transfer RNA analysis. In addition, we observed multiple functional signals in the C-terminal extensions of 34 maize SCR proteins, and characterized the structural and subcellular localization changes in the extended protein of BASIC TRANSCRIPTION FACTOR 3. Overall, our study not only demonstrates that SCR events are widespread in plants but also reveals the unprecedented recoding plasticity of stop codons, which provides important new insights into the flexibility of genetic decoding.

plant biology↗