The histone variant macroH2A suppresses melanoma progression through regulation of CDK8

Abstract

Cancer is a disease consisting of both genetic and epigenetic changes. While increasing evidence demonstrates that tumour progression entails chromatin-mediated changes such as DNA methylation, the role of histone variants in cancer initiation and progression currently remains unclear. Here, we report that the histone variant macroH2A (mH2A) suppresses tumour progression of malignant melanoma. Loss of mH2A isoforms, histone variants generally associated with condensed chromatin and fine-tuning of developmental gene expression programs1-4, is positively correlated with increasing malignant phenotype of melanoma cells in culture and human tissue samples. Knockdown of mH2A isoforms in melanoma cells of low malignancy results in significantly increased proliferation and migration in vitro and growth and metastasis in vivo. Restored expression of mH2A isoforms rescues these malignant phenotypes in vitro and in vivo. We demonstrate that the tumour promoting function of mH2A loss is mediated, at least in part, through direct transcriptional up-regulation of CDK8. Suppression of CDK8, a colorectal cancer oncogene5, 6, inhibits proliferation of melanoma cells, and knockdown of CDK8 in cells depleted of mH2A suppresses the proliferative advantage induced by mH2A loss. Moreover, a significant inverse correlation between mH2A and CDK8 expression levels exists in melanoma patient samples. Taken together, our results demonstrate that mH2A is a critical component of chromatin that suppresses the development of malignant melanoma, a highly intractable cutaneous neoplasm.

Tumor-suppressive effects of CDK8 in endometrial cancer cells

“…6,7,31,36,38 We observed that pLKO-sh-CDK8-2 works more efficiently in depleting CDK8 than pLKO-sh-CDK8-1 in AN3 CA cells, thus pLKO-sh-CDK8-2 was used for further analysis in this work. Besides these two sh-CDK8 constructs, an independent set of sh-CDK8 constructs that target different sequence of hCDK8 mRNA using the same pLKO vector, designated as "sh-CDK8-S#1" to "sh-CDK8-S#5" were purchased from Sigma: sh-CDK8-…”

“…Thus to further examine the notion that CDK8 inhibits the growth of endometrial cancer cells, we depleted CDK8 in AN3 CA cells by transducing the cells with pLKO.1-shRNAs, which were previously shown to specifically target CDK8. 6,7,31,36,38 Similar construct targeting GFP (sh-GFP) was used as the negative control. Transduced cells were selected by puromycin for over 2 wk, and the efficiency of CDK8 knockdown was verified by qRT-PCR and western blot.…”

“…6 In addition, loss of the histone variant macroH2A increases the expression of CDK8 in melanoma. 7 Importantly, knocking down CDK8 effectively blocks the proliferation of melanoma and colon cancer cells, [6][7][8]24 suggesting that gain of CDK8 is an important oncogenic determinant. An oncogenic role of CDK8 is also supported by studies of walleye dermal sarcoma, which is caused by walleye dermal sarcoma virus.…”

Histone variant H2A.Z.2: A novel driver of melanoma progression

“…Previous studies have shown H2A.Z to be overexpressed and play a role in other tumor types; however, these studies either focused solely on H2A.Z.1 or did not clearly distinguish between the isoforms. 5 We have demonstrated that both H2A.Z isoforms are highly expressed in melanoma and that high expression levels correlate with shorter survival of patients. Although we do not exclude a role for H2A.Z.1 in melanoma pathogenesis, we identified a distinct role for H2A.Z.2 as a mediator of melanoma cell proliferation.…”

“…4 We have previously identified the histone variant macroH2A as a tumor suppressor in melanoma that directly regulates expression of the cyclin-dependent kinase CDK8. 5 In addition, the chromatin remodeler ATRX, a negative regulator of macroH2A, can be used as a prognostic marker of melanoma. 6 Recently, we have reported a role for another variant of the H2A family, namely H2A.Z.2, in promoting proliferation of melanoma cells.…”