Methylation of SUV39H1 by SET7/9 results in heterochromatin relaxation and genome instability

Abstract

Suppressor of variegation 3-9 homolog 1 (SUV39H1), a histone methyltransferase, catalyzes histone 3 lysine 9 trimethylation and is involved in heterochromatin organization and genome stability. However, the mechanism for regulation of the enzymatic activity of SUV39H1 in cancer cells is not yet well known. In this study, we identified SET domain-containing protein 7 (SET7/9), a protein methyltransferase, as a unique regulator of SUV39H1 activity. In response to treatment with adriamycin, a DNA damage inducer, SET7/9 interacted with SUV39H1 in vivo, and a GST pull-down assay confirmed that the chromodomain-containing region of SUV39H1 bound to SET7/9. Western blot using antibodies specific for antimethylated SUV39H1 and mass spectrometry demonstrated that SUV39H1 was specifically methylated at lysines 105 and 123 by SET7/9. Although the half-life and localization of methylated SUV39H1 were not noticeably changed, the methyltransferase activity of SUV39H1 was dramatically down-regulated when SUV39H1 was methylated by SET7/ 9. Consequently, H3K9 trimethylation in the heterochromatin decreased significantly, which, in turn, led to a significant increase in the expression of satellite 2 (Sat2) and α-satellite (α-Sat), indicators of heterochromatin relaxation. Furthermore, a micrococcal nuclease sensitivity assay and an immunofluorescence assay demonstrated that methylation of SUV39H1 facilitated genome instability and ultimately inhibited cell proliferation. Together, our data reveal a unique interplay between SET7/9 and SUV39H1-two histone methyltransferases-that results in heterochromatin relaxation and genome instability in response to DNA damage in cancer cells.histone methylation | nonhistone posttranslational modifications

Histone modifications in DNA damage response

“…Moreover, the role of H3K4 methylation in nucleotide excision repair is interesting, and H3K4R mutation exerts different impacts on nucleotide excision repair on different genomic loci (Chaudhuri et al, 2009). In our previous studies, we also described the critical role of an H3K4 methyltransferase SET7/9 in DNA damage response and oxidative stress, but through methylating non-histone proteins Wang et al, 2013). At last, H3K23 trimethylation (H3K23me3), a novel characterized histone modification, is reported to blocks DNA damage in pericentric heterochromatin during meiosis in Tetrahymena (Papazyan et al, 2014).…”

“…At first, H3K9me3 is an essential histone marker of heterochromatin (Grewal and Jia, 2007). H3K9 methyltransferase SUV39H1 is required for the maintenance of heterochromatic state, and its methylation by SET7/9 impairs its enzymatic activity resulting in decreased H3K9me3 and heterochromatin instability (Peng and Karpen, 2009;Wang et al, 2013). Next, H3K9 methylation is important for the cellular response to DNA damage, but the role of H3K9 methylation is different at the early-stage and late-stage of DNA damage response.…”

KMTase Set7/9 is a critical regulator of E2F1 activity upon genotoxic stress

“…There have been several non-histone proteins reported as the substrates for Set7/9, including TAF10 (TATA box binding protein (TBP)-associated factor, 30 kDa), 9 oestrogen receptor a (ERa), 10 RelA, 11 PCAF (P300/CBP-associated factor), 12 Stat3, 13 Yap, 14 and Suv39h1. 15 However, in most cases the functional significance of this methylation is still not clear. The beststudied targets of Set7/9-mediated methylation are p53 16 and E2 promoter-binding factor 1 (E2F1), 17 transcription factors involved in regulation of DNA damage response (DDR).…”

Sirt7 inhibits Sirt1-mediated activation of Suv39h1

“…On the other hand, more compact constitutive heterochromatin, observed in Sirt7 deficient cells, might prevent opening of chromatin regions that are in need for DNA repair causing accumulation of DNA damage and accelerated aging. In fact, recent evidence points to the importance of temporary chromatin relaxation even within highly compacted constitutive heterochromatin to allow DNA repair during stress responses [35]. The clear increase of constitutive heterochromatin in Sirt7 mutant cells seems to be in contrast to increased relaxation of facultative rDNA heterochromatin, which is also apparent in Sirt7 KO cells.…”