Project description:Melanoma tumors are highly heterogeneous, comprising of different cell types that vary in their potential for growth and invasion. Heterogeneous expression of the Microphthalmia-associated Transcription Factor (MITF) and the POU domain transcription factor BRN2 (POU3F2) has been found in malignant melanoma. Changing expression of these transcription factors as the disease progresses has been linked to the metastatic mechanism of phenotype switching. We therefore investigated the effects of MITF and BRN2 expression in melanoma growth and metastasis. Depletion of MITF resulted in a cell population that had a slowed cell cycle progression, was less invasive in vitro and had hindered tumor and metastasis forming ability in mouse xenograft studies. BRN2 depletion left a cell population with intact proliferation and invasion in vitro; however metastatic growth was significantly reduced in the mouse xenograft model. These results suggest that the proliferative population within melanoma tumors express MITF, and both MITF and BRN2 are important for metastatic growth in vivo. This finding highlights the importance of BRN2 and MITF expression in development of melanoma metastasis.
Project description:The transcription factors PAX3 and MITF are required for the development of the neural crest and melanocyte lineage, and both proteins play important roles in melanoma cell growth and survival. PAX3 transcriptionally activates MITF expression during neural crest development, but the relationship between these transcription factors during melanocyte development and in melanoma cells is currently poorly understood. This study aimed to further our understanding of the interaction between transcriptional networks controlled by PAX3 and MITF by assessing the effect of siRNA-mediated knockdown of PAX3 and MITF in metastatic melanoma cell lines. The goals of this study were to determine (i) if PAX3 is required for maintaining expression of MITF in melanoma and melanocyte cell lines; (ii) whether PAX3 and MITF independently, or redundantly, influence growth and survival in melanoma cell lines; and (iii) to investigate the respective roles of PAX3 and MITF expression in melanoma cell differentiation. Microarrays were used to measure global changes in transcript expression in response to siRNA-mediated knockdown of PAX3 or MITF compared to non-targeting controls in two metastatic melanoma cells lines. RNA was isolated from two different metastatic melanoma cell lines 30 hours after one of four different treaments: (i) transfection with siRNA targeting PAX3; or (ii) transfection with siRNA targeting MITF; or (iii) or transfection with siRNA targeting luciferase (non-targeting negative control); or (iv) treatment with media only (control). Therefore, eight samples were used for gene expression profiling by using GeneChip arrays, with one replicate per cell line per treatment.
Project description:The transcription factors PAX3 and MITF are required for the development of the neural crest and melanocyte lineage, and both proteins play important roles in melanoma cell growth and survival. PAX3 transcriptionally activates MITF expression during neural crest development, but the relationship between these transcription factors during melanocyte development and in melanoma cells is currently poorly understood. This study aimed to further our understanding of the interaction between transcriptional networks controlled by PAX3 and MITF by assessing the effect of siRNA-mediated knockdown of PAX3 and MITF in metastatic melanoma cell lines. The goals of this study were to determine (i) if PAX3 is required for maintaining expression of MITF in melanoma and melanocyte cell lines; (ii) whether PAX3 and MITF independently, or redundantly, influence growth and survival in melanoma cell lines; and (iii) to investigate the respective roles of PAX3 and MITF expression in melanoma cell differentiation. Microarrays were used to measure global changes in transcript expression in response to siRNA-mediated knockdown of PAX3 or MITF compared to non-targeting controls in two metastatic melanoma cells lines.
Project description:The genetic changes underlying metastatic melanoma need to be deciphered to develop new and effective therapeutics. Previously, genome-wide microarray analyses of human melanoma identified two reciprocal gene expression programs, that included expression of mRNAs regulated by either transforming growth factor, beta 1 (TGFB1) pathways or microphthalmia-associated transcription factor (MITF)/SRY-box containing gene 10 (SOX10) pathways. We extend this knowledge to include gene expression analyses of 5 additional human melanoma lines, and show that these lines also fall into either TGFB1 or MITF/SOX10 gene expression groups. These mRNA expression studies were followed up by miRNA expression analyses. Microarray analyses were performed on 5 metastatic melanoma lines in 3 replicates. Standard Affymetrix protocols were used.
Project description:Melanoma tumors are highly heterogeneous, comprising of many cell populations that vary in their potential for growth and invasion. Differential transcription factor expression contributes to these phenotypic traits. BRN2, a member of the POU domain family of transcription factors is thought to play important roles in melanoma invasion and metastasis. However, how BRN2 functions during the metastatic process of melanoma remains largely unknown. We therefore investigated the effects of BRN2 expression in melanoma cells with no or low constitutive expression using a doxycycline-inducible system. Induction of BRN2 expression led to reduced proliferation and partial resistance to an inhibitor of mutated BRAF. Whole genome profiling analysis revealed novel targets and signaling pathway changes related to prevention of cell death induced by detachment from the extracellular matrix, known as anoikis resistance. Further investigation confirmed increased survival of BRN2 expressing cell lines in non-adherent conditions. Functionally, expression of BRN2 promoted induction of c-MET levels as well as increased phosphorylation of STAT3. Treatment with crizotinib, a c-MET inhibitor, decreased cellular viability of BRN2 expressing cells under non-adherent conditions to death by anoikis. These results highlight the importance of a largely overlooked transcription factor in the progression and metastasis of melanoma, and may suggest a strategy to target BRN2 expressing cells resistant to therapy and cell death by anoikis.
Project description:Cellular stress contributes to the capacity of melanoma cells to undergo phenotype switching into highly migratory and drug tolerant dedifferentiated states. Such dedifferentiated melanoma cell states are marked by loss of melanocyte specific gene expression and increase of mesenchymal markers. Two crucial transcription factors, MITF and SOX10, important in melanoma development and progression have been implicated in this process. In this study we describe that loss of MITF is associated with a distinct transcriptional program, MITF promoter hypermethylation and poor patient survival in metastatic melanoma. From a comprehensive collection of melanoma cell lines, we observed that MITF methylated cultures were subdivided in two distinct subtypes. Examining mRNA levels of neural crest associated genes we found that one subtype had lost the expression of several lineage genes including SOX10. Intriguingly, SOX10 loss was associated with SOX10 gene promoter hypermethylation and distinct phenotypic and metastatic properties. Depletion of SOX10 in MITF methylated melanoma cells using CRISPR/Cas9 confirmed these findings. In conclusion, this study describes the significance of melanoma state and the underlying functional properties explaining the aggressiveness of such states.
Project description:Metastatic melanoma is hallmarked by its ability to switch oncogenic MITF expression. Here we tested the impact of STAT3 on melanoma onset and progression in association with MITF expression levels. We established a mouse melanoma model for deleting Stat3 specifically in melanocytes with specific expression of human hyperactive NRASQ61K in an Ink4a deficient background. Mice with tissue specific Stat3 deletion showed an early onset of disease, but displayed significantly diminished lung metastasis. Whole genome expression profiling also revealed a reduced invasion phenotype, which was functionally confirmed in 3D melanoma model systems. Notably, loss or knockdown of STAT3 in mouse or human cells resulted in up-regulation of MITF and induction of cell proliferation. Mechanistically we show that STAT3 induced CEBPa/b expression was sufficient to suppress MITF transcription. Epigenetic analysis by ATAC-seq confirmed that STAT3 enabled CEBPa/b binding to the MITF enhancer region thereby silencing it. We conclude that STAT3 is a metastasis driver able to antagonize the MITF oncogene via direct induction of CEBP family member transcription facilitating RAS-RAF-driven melanoma metastasis.
Project description:The inherent ability of melanoma cells to alter the differentiation-associated transcriptional repertoire to evade treatment and facilitate metastatic spread is well accepted and has been termed phenotypic switching. However, how these facets of cellular behavior are controlled remains largely elusive. Here we show that cysteine availability, whether from lysosomes (CTNS-dependent) or exogenously derived (SLC7A11-dependent or as N-acetylcysteine), controls melanoma differentiation-associated pathways by acting on the melanocyte master regulator MITF. Functional data indicate that low cysteine availability reduces MITF levels and impairs lysosome functions, which affects tumor ferroptosis sensitivity but improves metastatic spread in vivo. Mechanistically, cysteine-restrictive conditions reduce acetyl-CoA levels to decrease p300-mediated H3K27 acetylation at the melanocyte-restricted MITF promoter, thus forming a cysteine feed-forward regulation that controls MITF levels and downstream lysosome functions. These findings collectively suggest that cysteine homeostasis governs melanoma differentiation by maintaining MITF levels and lysosome functions, which protect against ferroptosis and limit metastatic spread.