The role of KDM6A in melanoma
Melanoma is an aggressive form of skin cancer and the most common in young adults. Australia has one of the highest incidence of melanoma in the world. Current treatments for metastatic melanoma are plagued by the resistance these melanomas develop against current targeted therapies or immunotherapies.
Lysine demethylases (KDMs) are epigenetic enzymes that remove methyl groups from the amino acid lysine on histone proteins, which effects gene expression. One of these KDMs is KDM6A (also known as UTX), that removes methyl groups from type 3 histone, 3 lysine number 27 (H3K27me3) inducing activation of gene expression. KDM6A has been reported to play an important role in the progression of bladder cancer, multiple myeloma, lung cancer, cervical cancer and pancreatic cancer [1-5]however the role of KDM6A in melanoma is yet to be investigated.
In this study, we quantified KDM6A protein in 83 patients with cutaneous melanoma using immunohistochemistry (IHC) and correlated KDM6A expression with survival. We showed that 44% of patients had high KDM6A that lead to significant decreased survival compared to patients with low KDM6A. Hence, KDM6A has important clinical implications in melanoma and that targeting KDM6A in melanoma should be further investigated.
The inhibitor GSK-J4 which targets KDM6A activity was tested to investigate its effects on melanoma cell lines as well as normal human cells; melanocytes (HEM) and dermal fibroblasts (HDF). We showed that when melanoma cell lines are treated with GSK-J4 over 3 days, cell viability (cell titre glow assay) is significantly reduced compared to DMSO vehicle control in a dose-dependent manner. Additionally, cell viability was further reduced by treatment over 6 days, suggesting that melanoma cells sensitize to GSK-J4 treatment over a longer period of time. In addition, GSK-J4 treatment on HEMs and HDFs showed less cell death when compared to the melanoma cell lines, suggesting it in not toxic to normal cells.
To investigate the specificity of GSK-J4, immunofluorescence (IF) was used to measure global levels of H3K27me3 following treatment. IF showed that GSK-J4 treatment in a GSK-J4 sensitive melanoma cell line increased H3K27me3 levels compared to the control, as expected.
EZH2 (also known as KMT6A) is the antagonist of KDM6A in that it adds methyl groups to H3K27, typically associated with gene repression. We and others have demonstrated an oncogenic role for EZH2 in melanoma and EZH2 inhibitors can impede the growth of melanoma in vitro and in vivo [6, 7]. Importantly, several cancers with inactivating mutations in KDM6A, confer sensitivity to EZH2 inhibitors. The effects of GSK-J4 treatment in conjunction with an EZH2 inhibitor GSK126 was tested on a melanoma cell line highly resistant to GSK126 to determine if these cells were sensitive to concurrent KDM6A/EZH2 inhibitor treatment. We found that cell viability was significantly reduced by the combination, when compared to single drug treatment.
Our preliminary data suggests that targeting KDM6A with the inhibitor GSK-J4 could be a potential therapy in melanoma that should be further investigated.