Investigation of TFE3 and TFAP2B as critical regulators of melanoma cell plasticity

About This Grant

Summary Melanoma cells exhibit remarkable plasticity, transitioning between melanocytic/proliferative and mesenchymal/invasive states. This plasticity drives intra-tumoral heterogeneity, disease progression, and therapeutic resistance. While the Microphthalmia-associated Transcription Factor (MITF) is a well-established driver of the melanocytic/proliferative phenotype, the mesenchymal/invasive phenotype and the mechanisms governing state transitions remain poorly understood. Our published and preliminary data identify the MITF paralog TFE3 and the pioneer factor TFAP2B as critical regulators of the mesenchymal state in melanoma. We identify two TFE3 isoforms, a short length (TFE3sl) and a full-length (TFE3fl), with TFE3fl specifically stabilized in invasive melanoma. Pan-TFE3 knockout reduced invasion and distal lung seeding of MITF-low melanoma cell lines. Moreover, MITF directly suppresses the mesenchymal phenotype by activating FNIP2, a key component of the non-canonical mTORC1 signaling pathway. This pathway facilitates lysosomal degradation of TFE3fl, leading us to hypothesize that TFE3fl drives metastasis. These findings suggest a molecular mechanism in which the balance of transcriptional regulation by MITF and TFE3fl, in combination with TFAP2B, governs melanoma plasticity. We hypothesize that melanoma cell plasticity is regulated by a TFE3fl-TFAP2B axis that promotes mesenchymal phenotypes and metastatic progression. To test this hypothesis, we propose the following aims: (1) identify the TFE3 isoform critical for melanoma plasticity and progression and (2) determine how the TFAP2B/TFE3fl axis establishes mesenchymal states within primary tumors. To achieve these aims, we will use patient-derived melanoma cell lines and complementary in vivo models. Zebrafish are uniquely suited for this work because we have generated a primary melanoma model that enables direct visualization of vertical tumor cell invasion in real time, combined with histological validation across multiple animals, providing high-throughput assessment of invasive behavior in the correct anatomical context. In parallel, mouse models will be essential for assessing cancer stem cell (CSC) dynamics, including tumor cell survival and dissemination within the bloodstream, as well as long-term metastatic colonization and survival outcomes. Together, these approaches will allow us to define how TFE3 and TFAP2B regulate melanoma plasticity in both early invasive transitions and later metastatic progression. This study will advance our understanding of melanoma plasticity and identify mechanisms that facilitate the adaptive nature of melanoma cells. Use of mice and zebrafish in this proposal: The rationale for utilizing mouse and zebrafish models is that normal and pathological cells behave differently in vivo due to a complex microenvironment that cannot be replicated in other model systems. Zebrafish have the added benefit of real time imaging of melanoma onset and progression