LOXL2-mediated H3K4 oxidation reduces chromatin accessibility in triple-negative breast cancer cells

Oxidation of H3 at lysine 4 (H3K4ox) by lysyl oxidase-like 2 (LOXL2) generates an H3 modification with an unknown physiological function. We find that LOXL2 and H3K4ox are higher in triple-negative breast cancer (TNBC) cell lines and patient-derived xenografts (PDXs) than those from other breast cancer subtypes. ChIP-seq revealed that H3K4ox is located primarily in heterochromatin, where it is involved in chromatin compaction. Knocking down LOXL2 reduces H3K4ox levels and causes chromatin decompaction, resulting in a sustained activation of the DNA damage response (DDR) and increased susceptibility to anticancer agents. This critical role that LOXL2 and oxidized H3 play in chromatin compaction and DDR suggests that functionally targeting LOXL2 could be a way to sensitize TNBC cells to conventional therapy.This work was supported by grants from Instituto de Salud Carlos III (ISCIII) FIS/FEDER (PI12/01250; CP08/00223; PI16/00253; and CB16/12/00449), MINECO (SAF2013-48849-C2-1-R) to SP, BFU2015-68354 to THS, Breast Cancer Research Foundation (BCRF-17-008) to JA, AGL2014-52395-C2-2-R to DA, Worldwide Cancer Research, Red Temática de Investigación Cooperativa en Cáncer (RD012/0036/005), Fundación Científica de la Asociación Española contra el Cáncer, and Fundació La Marató TV3.THS was supported by institutional funding (MINECO) through theCentres of Excellence Severo Ochoa award and the CERCA Pro-gramme of the Catalan Government, and SS-B, by a Fundació LaCaixa fellowship. We thank La Caixa Foundation and Cellex Foun-dation for provide research facilities and equipment. GV has received f unding from the MINECO (a “Juan de la Cierva Incorporation ” fellowship; IJCI-2014-20723). SP was a recipient of a Miguel Servet contract (ISCIII/FIS), and AI, JPC-C, LP-G, and GS-B are supported by contracts from Worldwide Cancer Research, Fundació La MaratóTV3, Fundació FERO, and a FI Fellowship from the Generalitat de Catalunya, respectively