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

Abstract

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.

Lysyl Oxidase Like‐2 (LOXL2): An Emerging Oncology Target

“…[76] Furthermore, LOXL2-mediated oxidation of histone H3K4 is also higher in TNBC, and knock down experiment on LOXL2 resulted in reduced H3K4ox levels and sustained activation of the DNA damage response. [77] These findings are supported by the identification of LOXL2 upregulation in invasive metastatic breast cancer models, Hs578T and MDA-MB231, in comparison to poorly invasive breast cancers, MCF-7 and T47D. [51] RT-PCR analysis demonstrated LOXL2 mRNA expression to be upregulated in the cell lines, Hs578T and MDA-MB231 however not expressed in MCF-7 and T47D cell lines.…”

“…Patients with triple negative breast cancer (TNBC) had a statistically significant 12.3% higher rate of LOXL2‐positive expression than non‐TNBC . Furthermore, LOXL2‐mediated oxidation of histone H3K4 is also higher in TNBC, and knock down experiment on LOXL2 resulted in reduced H3K4ox levels and sustained activation of the DNA damage response …”

Maintaining oxidized H3 in heterochromatin is required for the oncogenic capacity of triple-negative breast cancer cells

“…We revisited a tandem-affinity purification approach previously published by our lab to identify putative LOXL2 interactors that might be involved in the maintenance or generation of compacted chromatin induced by H3K4ox-LOXL2 (Cebria-Costa et al, 2019;Herranz et al, 2016). Analysis of the new list of interactors showed the presence of two AAA+ ATPases (RUVBL1 and RUVBL2), DMAP1 and BAF53, all of which are members of the SRCAP and TIP60 complexes ( Figure 1A and Table S1).…”

“…In fact, this oxidation is linked to transcriptional repression of several genes and heterochromatin transcripts at the onset of the epithelial-to-mesenchymal transition (EMT) and during stem cell differentiation (Herranz et al, 2016;Iturbide et al, 2015;Millanes-Romero et al, 2013). However, this modified histone is mainly enriched in heterochromatin, where it could have a role in the maintenance of condensed/compacted chromatin regions (Cebria-Costa et al, 2019). Heterochromatin is also characterized by the presence of di-methylated and tri-methylated lysine 9 in histone H3 (H3K9me2/3) and tri-methylated lysine 27 in histone H3 (H3K27me3) (Allshire and Madhani, 2018;Janssen et al, DMAP1 interacted in HEK293T cells ( Figure 1B).…”

“…To determine whether RUVBL2 is necessary to recruit and maintain LOXL2 to chromatin, we analyzed the levels of LOXL2 and H3K4ox in the TNBC cell line MDA-MB-231 by subcellular fractionation; note that this breast cancer cell line was selected because it expresses high levels of LOXL2 and exhibits high H3K4ox (Cebria-Costa et al, 2019). Indeed, in shRUVBL2 cells, reduced levels of LOXL2 were detected in the chromatin fraction (as compared to shControl cells), suggesting that the presence of RUVBL2 is important to maintain LOXL2 into chromatin ( Figure 1I).…”