Malignant melanoma is an aggressive cancer known for its notorious resistance to most current therapies. The basic helix-loop-helix microphthalmia transcription factor (MITF) is the master regulator determining the identity and properties of the melanocyte lineage, and is regarded as a lineage-specific 'oncogene' that has a critical role in the pathogenesis of melanoma. MITF promotes melanoma cell proliferation, whereas sustained supression of MITF expression leads to senescence. By combining chromatin immunoprecipitation coupled to high throughput sequencing (ChIP-seq) and RNA sequencing analyses, we show that MITF directly regulates a set of genes required for DNA replication, repair and mitosis. Our results reveal how loss of MITF regulates mitotic fidelity, and through defective replication and repair induces DNA damage, ultimately ending in cellular senescence. These findings reveal a lineage-specific control of DNA replication and mitosis by MITF, providing new avenues for therapeutic intervention in melanoma. The identification of MITF-binding sites and gene-regulatory networks establish a framework for understanding oncogenic basic helix-loop-helix factors such as N-myc or TFE3 in other cancers.

The TEAD (1-4) transcription factors comprise the conserved TEA/ATTS DNA-binding domain recognising the MCAT element in the promoters of muscle-specific genes. Despite extensive genetic analysis, the function of TEAD factors in muscle differentiation has proved elusive due to redundancy among the family members. Expression of the TEA/ATTS DNA-binding domain that acts as a dominant negative repressor of TEAD factors in C2C12 myoblasts inhibits their differentiation, whereas selective shRNA knockdown of TEAD4 results in abnormal differentiation characterised by the formation of shortened myotubes. Chromatin immunoprecipitation coupled to array hybridisation shows that TEAD4 occupies 867 promoters including those of myogenic miRNAs. We show that TEAD factors directly induce Myogenin, CDKN1A and Caveolin 3 expression to promote myoblast differentiation. RNA-seq identifies a set of genes whose expression is strongly reduced upon TEAD4 knockdown among which are structural and regulatory proteins and those required for the unfolded protein response. In contrast, TEAD4 represses expression of the growth factor CTGF (connective tissue growth factor) to promote differentiation. Together these results show that TEAD factor activity is essential for normal C2C12 cell differentiation and suggest a role for TEAD4 in regulating expression of the unfolded protein response genes. The TEAD transcription factors make a highly conserved family of 4 DNA-binding proteins 1,2 containing the TEA (Yeast (TEC-1), Aspergillus nidulans (AbaA) and Drosophilla (scalloped))/ATTS (Aspergillus nidulans (AbaA), Yeast (TEC-1), human TEF1, and Drosophilla (scalloped)) DNA-binding domain (DBD). 3,4 The TEA domain comprises a three-helix bundle with a homeodomain fold and binds a consensus MCAT (5 0 -CATTCCA/ T-3 0 ) element originally defined as the GT-II motif of the simian virus 40 (SV40) enhancer. 5 Mammalian TEADs are widely expressed with prominent expression in the nervous system and muscle. In-vitro, cell-based, knockout and transgenic studies have addressed the role of TEAD factors in regulation of muscle-expressed genes. 6-8 Cardiac troponin T, myosin, heavy polypeptide 7, cardiac muscle, beta (b-MHC) and Myocardin, have functional MCAT motifs in their regulatory regions. 2 Stimulation of a1-adrenergic signalling has been shown to induce cardiac hypertrophy and activate transcription of the b-MHC and skeletal a-actin genes in an MCAT-and TEAD-dependent manner in cultured neonatal rat cardiomyocytes. 9 Cardiac muscle-specific overexpression of TEAD4 in transgenic mice has been shown to induce arhythmias in vivo. 8 TEAD4 is specifically expressed in developing skeletal muscle in mouse embryos. 1 Chromatin immunoprecipitation-array hybridization (ChIP-chip) showed that TEAD4 is a direct target of the MYOD1 and MYOG transcription factors in C2C12 cells. 10 Although TEAD4 upregulation by MYOD1 and MYOG during differentiation is thought to activate transcription of muscle structural genes, mouse knockouts do not show any evident role for TEAD4 i...