Loss of the N-terminal methyltransferase NRMT1 increases sensitivity to DNA damage and promotes mammary oncogenesis

Abstract

Though discovered over four decades ago, the function of N-terminal methylation has mostly remained a mystery. Our discovery of the first mammalian N-terminal methyltransferase, NRMT1, has led to the discovery of many new functions for N-terminal methylation, including regulation of DNA/protein interactions, accurate mitotic division, and nucleotide excision repair (NER). Here we test whether NRMT1 is also important for DNA double-strand break (DSB) repair, and given its previously known roles in cell cycle regulation and the DNA damage response, assay if NRMT1 is acting as a tumor suppressor. We find that NRMT1 knockdown significantly enhances the sensitivity of breast cancer cell lines to both etoposide treatment and γ-irradiation, as well as, increases proliferation rate, invasive potential, anchorage-independent growth, xenograft tumor size, and tamoxifen sensitivity. Interestingly, this positions NRMT1 as a tumor suppressor protein involved in multiple DNA repair pathways, and indicates, similar to BRCA1 and BRCA2, its loss may result in tumors with enhanced sensitivity to diverse DNA damaging chemotherapeutics.

Structural basis for substrate recognition by the human N-terminal methyltransferase 1

“…This methylation of DDB2 promotes its recruitment to form foci at the sites of DNA damage and facilitates nucleotide excision repair, possibly indicating a role of NTMT1 in the DNA damage response (DDR) network (Cai et al 2014). Moreover, knockdown of NTMT1 leads to hypersensitivity of breast cancer cell lines to both etoposide and γ-irradiation treatments, further suggesting NTMT1 as a component of DDR (Bonsignore et al 2015a). Interestingly, NTMT1 knockout mice suffer a high mortality rate shortly after birth and exhibit premature aging and phenotypes characteristic of mouse models deficient for DDR molecules, indicating the biological significance of NTMT1 in vivo (Bonsignore et al 2015b).…”

Chemical Biology of Protein N‐Terminal Methyltransferases

“…Additionally, NTMT1 is overexpressed in tumor tissues of patients, including colorectal, melanoma, carcinoid, lung, and liver, according to ProteinAtlas (http://www.proteinatlas.org). Knockdown of NTMT1 results in mitotic defects and sensitizes etoposide and gamma irradiation in breast cancer cell lines such as MCF‐7 and LCC9, whereas NTMT1 knockout mice showed premature aging . Both studies infer the function of NTMT1 in DNA damage repair.…”

Alpha-amino methylation and acetylation are novel regulators of MYL9 function.

“…Additionally, a number of mutations in NRMT1 that decrease catalytic activity have been associated with cancers, and knockdown of this enzyme has been shown to increase mammary tumorigenesis (Bonsignore, Butler et al 2015, Shields, Tooley et al 2017. A mutation in NAA10, the catalytic subunit of NatA, results in the lethal X-linked developmental disorder Ogden syndrome (Van Damme, Stove et al 2014, Myklebust, Van Damme et al 2015.…”

“…First, mice lacking NRMT1 are small in size, show signs of prematuring aging (including graying and kyphosis), exhibit female-specific infertility, and have a high rate of morbidity by 6 months of age . NRMT1 misregulation and mutation are observed in a variety of cancers (Sabates-Bellver, Van der Flier et al 2007, Brune, Tiacci et al 2008, Finak, Bertos et al 2008, and NRMT1 knockdown (KD) increases the rate of tumor growth in a breast cancer xenograft model (Bonsignore, Butler et al 2015).…”

“…Until recently, Nαmethylation was thought to be a general promoter of protein stability, as it was originally identified as a modification that protected cytochrome c from degradation Smith 1977, Smith andPettigrew 1980). We and others have now shown that it also facilitates the protein-DNA interaction of substrates such as RCC1, CENP-A, CENP-B, and DDB2, and thus, plays an important role in the maintenance of genome integrity (Chen, Muratore et al 2007, Dai, Otake et al 2013, Cai, Fu et al 2014, Bonsignore, Butler et al 2015, Sathyan, Fachinetti et al 2017. While several transcription factors are substrates of NRMT1, it has not yet been experimentally demonstrated that Nα-methylation plays a role in transcriptional regulation (Tooley, Petkowski et al 2010, Petkowski, Schaner Tooley et al 2012).…”