H3K9 Histone Methyltransferase G9a Promotes Lung Cancer Invasion and Metastasis by Silencing the Cell Adhesion Molecule Ep-CAM

Abstract

G9a is a mammalian histone methyltransferase that contributes to the epigenetic silencing of tumor suppressor genes. Emerging evidence suggests that G9a is required to maintain the malignant phenotype, but the role of G9a function in mediating tumor metastasis has not been explored. Here, we show that G9a is expressed in aggressive lung cancer cells, and its elevated expression correlates with poor prognosis. RNAi-mediated knockdown of G9a in highly invasive lung cancer cells inhibited cell migration and invasion in vitro and metastasis in vivo. Conversely, ectopic G9a expression in weakly invasive lung cancer cells increased motility and metastasis. Mechanistic investigations suggested that repression of the cell adhesion molecule Ep-CAM mediated the effects of G9a. First, RNAi-mediated knockdown of Ep-CAM partially relieved metastasis suppression imposed by G9a suppression. Second, an inverse correlation between G9a and Ep-CAM expression existed in primary lung cancer. Third, Ep-CAM repression was associated with promoter methylation and an enrichment for dimethylated histone H3K9. G9a knockdown reduced the levels of H3K9 dimethylation and decreased the recruitment of the transcriptional cofactors HP1, DNMT1, and HDAC1 to the Ep-CAM promoter. Our findings establish a functional contribution of G9a overexpression with concomitant dysregulation of epigenetic pathways in lung cancer progression. Cancer Res; 70(20); 7830-40. ©2010 AACR.

Inhibition of histone H3K9 methyltransferases by gliotoxin and related epipolythiodioxopiperazines

“…Indeed, overexpression of G9a is associated with several types of cancers and downregulation of G9a by RNAi inhibits tumor cell proliferation. [7][8][9] Chaetocin and BIX-01294 are small molecules that inhibit histone H3K9 HMTs. Chaetocin, which inhibit both G9a and Suv39h activities, is a member of the epipolythiodioxopiperazine (ETP) class of fungal metabolites.…”

S -adenosyl methionine is necessary for inhibition of the methyltransferase G9a by the lysine 9 to methionine mutation on histone H3

“…Unmodified H3 [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] peptide (23 μM) was incubated with 25 nM G9a-SET in the presence of 50 μM SAM (radioactive: nonradioactive molar ratio = 0.016) in a buffer containing 50 mM Hepes (pH 7.9), 0.5 mM DTT, 0.25 mM PMSF, and 2 mM MgCl 2 . Where applicable, different H3 1-20 K9X peptides (Tufts University Peptide Synthesis Core) were present in the reaction.…”

“…Recent studies identified a role for G9a in heterochromatin maintenance and transcriptional repression, such as the silencing of repeat elements, including long interspersed nuclear elements and endogenous retroviruses (12)(13)(14). Up-regulation of both G9a and G9a like protein (GLP) has implications in a variety of human cancers, including solid tumors as well as acute myeloid leukemia (15)(16)(17). Here, we present biochemical and structural evidence that the histone H3K9M peptide inhibits G9a activity by effectively competing with WT histone H3 substrate peptide for binding to the active site.…”

Human heterochromatin protein 1 isoforms regulate androgen receptor signaling in prostate cancer

“…Similarly, HP1a expression is upregulated in various tumor tissues in contrast to the corresponding normal tissues without detectable HP1a expression, as well as in highly malignant breast cancers with poor patient survival (De Koning et al 2009). In addition, HP1-related methyltransferase G9a has been reported to promote lung cancer invasion and metastasis (Chen et al 2010). In addition, we have recently shown that HP1b is upregulated with an increased Gleason score in prostate cancer (Shiota et al 2010a).…”