NF-κB-induced R-loop accumulation and DNA damage select for nucleotide excision repair deficiencies in adult T cell leukemia

Constitutive NF-kappa B activation (NF-kappa B-CA) confers survival and proliferation advantages to cancer cells and frequently occurs in T/B cell malignancies including adult T cell leukemia (ATL) caused by human T-cell leukemia virus type 1 (HTLV-1). Counterintuitively, NF-kappa B-CA by the HTLV-1 transactivator/oncoprotein Tax induces a senescence response, and HTLV-1 infections in culture mostly result in senescence or cell-cycle arrest due to NF-kappa B-CA. How NF-kappa B-CA induces senescence, and how ATL cells maintain NF-kappa B-CA and avert senescence, remain unclear. Here we report that NF-kappa B-CA by Tax increases R-loop accumulation and DNA double-strand breaks, leading to senescence. R-loop reduction via RNase H1 overexpression, and short hairpin RNA silencing of two transcription-coupled nucleotide excision repair (TC-NER) endonucleases that are critical for R-loop excision-Xeroderma pigmentosum F (XPF) and XPG-attenuate Tax senescence, enabling HTLV-1-infected cells to proliferate. Our data indicate that ATL cells are often deficient in XPF, XPG, or both and are hypersensitive to ultraviolet irradiation. This TC-NER deficiency is found in all ATL types. Finally, ATL cells accumulate R-loops in abundance. Thus, TC-NER deficits are positively selected during HTLV-1 infection because they facilitate the out-growth of infected cells initially and aid the proliferation of ATL cells with NF-kappa B-CA later. We suggest that TC-NER deficits and excess R-loop accumulation represent specific vulnerabilities that may be targeted for ATL treatment.

Automated summary

Constitutive NF-kappa B activation induces senescence through R-loop accumulation and DNA double-strand breaks, while ATL cells exhibit deficiencies in TC-NER endonucleases and accumulate R-loops. These vulnerabilities may serve as potential targets for ATL treatment.