Renck Nunes, P. | Search bioRxiv

bioRxiv2025

TERRA R-loops trigger a switch in telomere maintenance towards break-induced replication and PrimPol-dependent repair

TERRA long noncoding RNAs associate with telomeres post transcription through base-pairing with telomeric DNA forming R-loop structures. TERRA regulates telomere maintenance but its exact modes of action remain unknown. Here, we induce TERRA transcription and R-loop formation in telomerase-expressing cells and determine that TERRA R-loop formation requires non-redundant functions of the RAD51 DNA recombinase and its enhancer RAD51AP1. TERRA R-loops interfere with semiconservative DNA replication promoting telomere maintenance by a homology-directed repair (HDR) mechanism known as Break Induced Replication (BIR), which ensures telomere maintenance in ALT cancer cells. In addition, TERRA induced PrimPol-dependent repair, which can initiate DNA synthesis de novo downstream of replication obstacles. PrimPol acts in parallel to BIR for telomere maintenance of TERRA over-expressing cells promoting their survival. Similarly, we find that PrimPol depletion is synthetic lethal with BIR deficiency in U2OS ALT cancer cells. Therefore, in the absence of other ALT-typical telomeric chromatin changes, TERRA R-loops per se are sufficient to induce ALT-typical telomere repair mechanisms.

molecular biology↗

bioRxiv2022

A therapeutically targetable NOTCH1-SIRT1-KAT7 axis in T-cell Leukemia

T-cell Acute Lymphoblastic Leukemia (T-ALL) is a NOTCH1-driven disease in need of novel therapies. Here, we identify a NOTCH1-SIRT1-KAT7 link as a therapeutic vulnerability in T-ALL, in which SIRT1 is overexpressed downstream of a novel NOTCH1-bound enhancer. SIRT1 loss impairs leukemia generation, while SIRT1 overexpression accelerates leukemia and confers resistance to NOTCH1 inhibition in a deacetylase-dependent manner. Moreover, secondary SIRT1 loss extends survival and synergizes with NOTCH1 inhibition. Global acetyl-proteomics upon SIRT1 loss uncovered hyperacetylation of KAT7 and BRD1, subunits of a histone acetyltransferase complex targeting H4K12. Metabolic and gene expression profiling revealed a metabolic crisis together with a transcriptional signature resembling KAT7 deletion. Consistently, SIRT1 loss resulted in reduced H4K12ac, and overexpression of a non-acetylatable KAT7 mutant partly rescued SIRT1 loss-induced proliferation defects. The newly unveiled NOTCH1-SIRT1-KAT7 axis uncovers novel therapeutic targets in T-ALL and reveals a circular feedback mechanism balancing deacetylase/acetyltransferase activation with potentially broad relevance in cancer. Statement of significanceWe identified a novel axis in T-ALL whereby NOTCH1 activates SIRT1 through an enhancer region, and SIRT1 deacetylates and activates KAT7. Targeting SIRT1 shows antileukemic effects, partly mediated by KAT7 inactivation. Our results identify novel therapeutic targets and uncover a rheostat mechanism between deacetylase/acetyltransferase activities with potentially broader cancer relevance.

cancer biology↗