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Background: Genomic studies have revealed that multiple genes are mutated at varying frequency in endometrial cancer (EC); however, the relevance of many of these mutations is poorly understood. An EC-specific recurrent mutation in the MAX transcription factor p.His28Arg was recently discovered. We sought to assess the functional consequences of this hotspot mutation and determine its association with cancer-relevant phenotypes., Methods: MAX was sequenced in 509 endometrioid ECs, and associations between mutation status and clinicopathologic features were assessed. EC cell lines stably expressing MAXH28R were established and used for functional experiments. DNA binding was examined using electrophoretic mobility shift assays and chromatin immunoprecipitation. Transcriptional profiling was performed with microarrays. Murine flank (six to 11 mice per group) and intraperitoneal tumor models were used for in vivo studies. Vascularity of xenografts was assessed by MECA-32 immunohistochemistry. The paracrine pro-angiogenic nature of MAXH28R-expressing EC cells was tested using microfluidic HUVEC sprouting assays and VEGFA enzyme-linked immunosorbent assays. All statistical tests were two-sided., Results: Twenty-two of 509 tumors harbored mutations in MAX, including 12 tumors with the p.His28Arg mutation. Patients with a MAX mutation had statistically significantly reduced recurrence-free survival (hazard ratio = 4.00, 95% confidence interval = 1.15 to 13.91, P = .03). MAXH28R increased affinity for canonical E-box sequences, and MAXH28R-expressing EC cells dramatically altered transcriptional profiles. MAXH28R-derived xenografts statistically significantly increased vascular area compared with MAXWT and empty vector tumors (P = .003 and P = .008, respectively). MAXH28R-expressing EC cells secreted nearly double the levels of VEGFA compared with MAXWT cells (P = .03, .005, and .005 at 24, 48, and 72 hours, respectively), and conditioned media from MAXH28R cells increased sprouting when applied to HUVECs., Conclusion: These data highlight the importance of MAX mutations in EC and point to increased vascularity as one mechanism contributing to clinical aggressiveness of EC.

Mus spretus mice are highly resistant to several types of cancer compared to Mus musculus mice. To determine whether differences in microRNA (miRNA) expression account for some of the differences in observed skin cancer susceptibility between the strains, we performed miRNA expression profiling of skin RNA for over 300 miRNAs. Five miRNAs, miR-1, miR-124a-3, miR-133a, miR-134, miR-206, were differentially expressed by array and/or qPCR. miR-1 was previously shown to have tumor suppressing abilities in multiple tumor types. We found miR-1 expression to be lower in mouse cutaneous squamous cell carcinomas (cSCCs) compared to normal skin. Based on the literature and our expression data, we performed detailed studies on predicted miR-1 targets and evaluated the effect of miR-1 expression on two murine cSCC cell lines, A5 and B9. Following transfection of miR-1, we found decreased mRNA expression of three validated miR-1 targets, Met, Twf1 and Ets1 and one novel target Bag4. Decreased expression of Ets1 was confirmed by Western analysis and by 3' reporter luciferase assays containing wildtype and mutated Ets1 3'UTR. We evaluated the effect of miR-1 on multiple tumor phenotypes including apoptosis, proliferation, cell cycle and migration. In A5 cells, expression of miR-1 led to decreased proliferation compared to a control miR. miR-1 expression also led to increased apoptosis at later time points (72 and 96 h) and to a decrease in cells in S-phase. In summary, we identified five miRNAs with differential expression between cancer resistant and cancer susceptible mice and found that miR-1, a candidate tumor suppressor, has targets with defined roles in tumorigenesis.