Histone demethylase AMX-1 is necessary for proper sensitivity to interstrand crosslink DNA damage

Abstract

Histone methylation is dynamically regulated to shape the epigenome and adjust central nuclear processes including transcription, cell cycle control and DNA repair. Lysine-specific histone demethylase 2 (LSD2) has been implicated in multiple types of human cancers. However, its functions remain poorly understood. This study investigated the histone demethylase LSD2 homolog AMX-1 in C. elegans and uncovered a potential link between H3K4me2 modulation and DNA interstrand crosslink (ICL) repair. AMX-1 is a histone demethylase and mainly localizes to embryonic cells, the mitotic gut and sheath cells. Lack of AMX-1 expression resulted in embryonic lethality, a decreased brood size and disorganized premeiotic tip germline nuclei. Expression of AMX-1 and of the histone H3K4 demethylase SPR-5 is reciprocally up-regulated upon lack of each other and the mutants show increased H3K4me2 levels in the germline, indicating that AMX-1 and SPR-5 regulate H3K4me2 demethylation. Loss of AMX-1 function activates the CHK-1 kinase acting downstream of ATR and leads to the accumulation of RAD-51 foci and increased DNA damage-dependent apoptosis in the germline. AMX-1 is required for the proper expression of mismatch repair component MutL/MLH-1 and sensitivity against ICLs. Interestingly, formation of ICLs lead to ubiquitination-dependent subcellular relocalization of AMX-1. Taken together, our data suggest that AMX-1 functions in ICL repair in the germline.

Histone Demethylase AMX-1 Regulates Fertility in a p53/CEP-1 Dependent Manner

“…Therefore, given that the lack of amx-1 results in upregulation of both Piwis (prg-1 and prg-2) and both transposons (Tc3 and Tc1), it is reasonable that the loss of AMX-1 result in broader impacts on biological pathways, not just restricted to defects in prg-1. Consistent with this idea, we reported that AMX-1 functions in spare roles in addition to the DNA damage-induced pathway (Zhang et al, 2021). Residual apoptosis found in cep-1;amx-1 double mutants compared with cep-1 single advocates the additional function of AMX-1.…”

“…Since all three histone demethylases belong to LSD1/2 homologs, which are involved in chromatin remodeling and modulating gene expressions, it has been considered that they may perform similar and redundant functions, thus compensating one another. Consistent with this idea, both AMX-1 and SPR-5 are implicated in fertility defect, sterility and lifespan ( Katz et al, 2009 ; Greer et al, 2016 ; Zhang et al, 2021 ), thus connecting fertility with histone methylation status. However, since SPR-5 and AMX-1 are implicated in DNA double-strand break repair (DSBR) and Interstrand Crosslink Repair (ICLR), respectively ( Wang et al, 2020 ; Zhang et al, 2021 ), we postulate that phenotypes observed in two histone demethylases might originate from separate pathways.…”

“…Consistent with this idea, both AMX-1 and SPR-5 are implicated in fertility defect, sterility and lifespan ( Katz et al, 2009 ; Greer et al, 2016 ; Zhang et al, 2021 ), thus connecting fertility with histone methylation status. However, since SPR-5 and AMX-1 are implicated in DNA double-strand break repair (DSBR) and Interstrand Crosslink Repair (ICLR), respectively ( Wang et al, 2020 ; Zhang et al, 2021 ), we postulate that phenotypes observed in two histone demethylases might originate from separate pathways.…”

“…The amx-1 deletion mutant ( ok659 ) was provided by the C. elegans Gene Knockout Project at the Oklahoma Medical Research Foundation, which was part of the International C. elegans Gene Knockout Consortium. amx-1 mutant (ok659) carries a 2636 bp deletion encompassing the entire SWIRM domain and most of the amine oxidase domain ( Zhang et al, 2021 ). amx-1(ok659) worms were outcrossed to the wild-type N2 and balanced with qC1 with roller and GFP markers for maintenance.…”

“…To examine AMX-1 histone demethylase level in vivo , dissected gonads from amx-1 age-matched adult hermaphrodites were probed for H3K4me2. To ensure that both control and mutant animals were processed and imaged under identical conditions, we dissected the both types of animals on the same slide as described in Zhang et al (2021) . Fluorescent intensity signal is sampled from multiple nuclei from different gonads and quantitated by using ImageJ or GelQuantNet.…”