Project description:Tumor cells increase glutamate release through the cystine/glutamate transporter xCT to balance oxidative homeostasis in tumor cells and promote tumor progression. Here, we demonstrated that although inhibition of xCT either by pharmacological inhibitor (sulfasalazine, SAS), approved by FDA for inflammatory diseases, or genetic knockdown induced ROS-related death in melanoma cells. Taken together, our results reveal that inhibition of xCT by SAS is a promising therapeutic strategy for melanoma.
Project description:Cutaneous malignant melanoma (CMM) lacks targeted therapies beyond the oft-circumvented BRAF inhibitors. Part of the difficulty in treating melanomas has been attributed to a strong survival program controlled by melanocyte transcription factors such as MITF - a phenomenon first described in melanoma as “lineage dependency.” Recently, a highly selective covalent CDK7 inhibitor (THZ1) has been shown to potently suppress the growth of various cancers through the depletion of master transcription-regulating oncogenes and the disruption of their attendant super-enhancers. We now show that melanoma cells are highly sensitive to CDK7 inhibition and that a melanocyte “lineage cluster,” whose members are transcriptionally driven by super-enhancers, is also strongly suppressed by THZ1. These results point to CDK7 inhibition as a viable strategy to deprive oncogenic transcription and suppress tumor growth in melanoma.
Project description:Cutaneous malignant melanoma (CMM) lacks targeted therapies beyond the oft-circumvented BRAF inhibitors. Part of the difficulty in treating melanomas has been attributed to a strong survival program controlled by melanocyte transcription factors such as MITF - a phenomenon first described in melanoma as “lineage dependency.” Recently, a highly selective covalent CDK7 inhibitor (THZ1) has been shown to potently suppress the growth of various cancers through the depletion of master transcription-regulating oncogenes and the disruption of their attendant super-enhancers. We now show that melanoma cells are highly sensitive to CDK7 inhibition and that a melanocyte “lineage cluster,” whose members are transcriptionally driven by super-enhancers, is also strongly suppressed by THZ1. These results point to CDK7 inhibition as a viable strategy to deprive oncogenic transcription and suppress tumor growth in melanoma.
Project description:The epigenetic modifier EZH2 is part of the polycomb repressive complex that suppresses gene expression via histone methylation. Activating mutations in EZH2 are found in a subset of melanoma that contributes to disease progression by inactivating tumor suppressor genes. In this study we have targeted EZH2 with a specific inhibitor (GSK126) or depleted EZH2 protein by stable shRNA knockdown. We show that inhibition of EZH2 has potent effects on the growth of both wild-type and EZH2 mutant human melanoma in vitro particularly in cell lines harboring the EZH2Y646 activating mutation. This was associated with cell cycle arrest, reduced proliferative capacity in both 2D and 3D culture systems, and induction of apoptosis. The latter was caspase independent and mediated by the release of apoptosis inducing factor (AIFM1) from mitochondria. Gene expression arrays showed that several well characterized tumor suppressor genes were reactivated by EZH2 inhibition. This included activating transcription factor 3 (ATF3) that was validated as an EZH2 target gene by ChIP-qPCR. These results emphasize a critical role for EZH2 in the proliferation and viability of melanoma and highlight the potential for targeted therapy against EZH2 in treatment of patients with melanoma. Tiffen JC, Gunatilake D, Gallagher SJ, Gowrishankar K, Heinemann A, Cullinane C, et al. Targeting activating mutations of EZH2 leads to potent cell growth inhibition in human melanoma by derepression of tumor suppressor genes. Oncotarget 2015;12:12
Project description:LNK (SH2B3) is a key negative regulator of JAK-STAT signaling which has been extensively studied in malignant hematopoietic diseases. We found that LNK is significantly elevated in cutaneous melanoma; this elevation is correlated with hyperactive signaling of the RAS-RAF-MEK pathway. Elevated LNK enhances cell growth and survival in adverse conditions. Forced expression of LNK inhibits signaling by interferon-STAT1 and suppresses interferon (IFN) induced cell cycle arrest and cell apoptosis. In contrast, silencing LNK expression by either shRNA or CRISPR-Cas9 potentiates the killing effect of IFN. The IFN-LNK signaling is tightly regulated by a negative feedback mechanism; melanoma cells exposed to IFN upregulate expression of LNK to prevent overactivation of this signaling pathway. Our study reveals an unappreciated function of LNK in melanoma and highlights the critical role of the IFN-STAT1-LNK signaling axis in this potentially devastating disease. LNK may be further explored as a potential therapeutic target for melanoma immunotherapy.
Project description:Immune checkpoint blockers (ICBs) showed unprecedented clinical benefits. But the overall efficacy of ICBs is limited to a small subset of cancer patients due to therapeutic resistance. Concerted efforts from our group and others have identified that loss of IFN-g signaling genes in melanoma is a major mechanism of resistance to ICBs. We therefore generated B16 melanoma model with IFNgR1 knocked out by CRISPR-Cas9. We sequenced the whole transcriptomes and identified activated PI3K-Akt-mTOR pathway in IFNgR1 knocked out cells. This may represent an attractive target for therapeutic interventions to bypassing ICB resistance in melanoma lacking functional IFN-g signaling.
Project description:In order to reveal the downstream targets of MAPK in melanoma, we measured the expression of 12 melanoma cell lines pre and post MEK inhibition Samples were treated with 50nM of the MEK inhibitor PD901 and collected 8 hours after treatment