The histone methyltransferase SMYD2 is a novel therapeutic target for the induction of apoptosis in ovarian clear cell carcinoma cells

Abstract

Previous studies have suggested that histone methylation can modulate carcinogenesis and cancer progression. For instance, the histone methyltransferase SET and MYND domain containing 2 (SMYD2) is overexpressed in several types of cancer tissue. The aim of the present study was to determine whether SMYD2 could serve a therapeutic role in ovarian clear cell carcinoma (OCCC). Reverse transcription-quantitative PCR was used to examine SMYD2 expression in 23 clinical OCCC specimens. Moreover, OCCC cell proliferation and cell cycle progression were also examined following small interfering RNA-mediated SMYD2 silencing or treatment with a selective SMYD2 inhibitor. SMYD2 was significantly upregulated in clinical OCCC specimens, compared with normal ovarian tissue. In addition, SMYD2 knockdown decreased cell viability as determined via a Cell Counting Kit-8 assay. Moreover, the proportion of cells in the sub-G₁ phase increased following SMYD2 knockdown, suggesting increased apoptosis. Treatment with the SMYD2 inhibitor LLY-507 suppressed OCCC cell viability. These results suggested that SMYD2 could promote OCCC viability, and that SMYD2 inhibition induced apoptosis in these cells. Thus, SMYD2 inhibitors may represent a promising molecular targeted approach for OCCC treatment.

Keywords: SMYD2; SMYD2 selective inhibitor; epigenetic modification; histone methyltransferase; ovarian clear cell carcinoma.

Figure 1.

SMYD2 expression in OCCC. (A) Histone methyltransferase mRNA levels in OCCC clinical samples and normal ovarian samples. The data are displayed as box plots with the median, the average (represented by Xs), the maximum and minimum, the interquartile ranges and the outliers (represented by circles). (B) SMYD2 expression levels in individual study participants. The data is displayed as the mean ± SD. *P<0.05. N.S., not significant; OCCC, ovarian clear cell carcinoma; EZH2, enhancer of zeste 2 polycomb repressive complex 2 subunit; SMYD, SET and MYND domain containing 2; SETD, SET domain containing lysine methyltransferase; SUV39H2, suppressor of variegation 3–9 homolog 2; EHMT2, euchromatic histone lysine methyltransferase 2.

Figure 2.

SMYD2 silencing attenuates proliferation of ovarian clear cell carcinoma cell lines. (A) SMYD2 knockdown was confirmed in OVTOKO and OVISE cells by western blotting following transfection with siSMYD2#1 and #2. (B) Semi-quantitative results of SMYD2 expression following siSMYD2 transfection. (C) SMYD2 knockdown significantly inhibits OVTOKO and OVISE cell proliferation. **P<0.01. SMYD, SET and MYND domain containing 2; si, small interfering; NC, negative control.

Figure 3.

SMYD2 inhibition suppresses the proliferation of ovarian clear cell carcinoma cell lines. OVTOKO, TOV21-G and OVMANA cells were treated with LLY-507, a selective SMYD2 inhibitor, at concentrations ranging from 0.001–10 µM. IC₅₀ values are presented below the dose-response curve. SMYD, SET and MYND domain containing 2.

Figure 4.

SMYD2 silencing induces apoptosis in OCCC cells. (A) SMYD2 and PARP protein expression in OCCC cell lines transfected with siSMYD2. (B) Frequency of cells in sub-G₁ phase following siSMYD2 knockdown. An accumulation of cells in sub-G₁ phase is indicative of increased apoptosis. *P<0.05. OCCC, ovarian clear cell carcinoma; SMYD2, SET and MYND domain containing 2; PARP, poly ADP ribose polymerase; si, small interfering; NC, negative control.