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15417786mcr200992-sup-255692_2_supp_7092465_qslvsh.pptx (845 kB)

Figure S6 from Mastermind Like Transcriptional Coactivator 3 (MAML3) Drives Neuroendocrine Tumor Progression

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posted on 2023-04-03, 19:45 authored by Nathaniel Alzofon, Katrina Koc, Kristin Panwell, Nikita Pozdeyev, Carrie B. Marshall, Maria Albuja-Cruz, Christopher D. Raeburn, Katherine L. Nathanson, Debbie L. Cohen, Margaret E. Wierman, Katja Kiseljak-Vassiliades, Lauren Fishbein

Western blot for expression of FL and dEx1 MAML3 domain constructs and luciferase assay. Cells for these blots were transfected at the same time as cells used for the luciferase experiment and harvested on the day the luciferase assay was performed. A. Protein expression of FL MAML3 domain constructs: FLâ^†C772 contains amino acids (aa) 1-772, FLâ^†C364 aa 1-364, FLâ^†Q aa 1-364 and 772-1133, FLâ^†S aa 1-195 and 365-1133, FLâ^†Nâ^†S aa 1-155 and 365-1133. B. Protein expression of dEx1 MAML3 domain constructs: dEx1â^†C772 contains amino acids (aa) 156-772, dEx1â^†C364 aa 156-364, dEx1â^†Q aa156-364 and 772-1133, dEx1â^†S aa 156-195 and 365-1133, dEx1â^†Nâ^†S aa 365-1133. C. TCF/LEF promoter activation by MAML3 constructs in QGP-1 and BON-1. Diagrams of each MAML3 construct are shown to the left of their relative promoter activation. All MAML3 constructs were co-transfected with β-catenin. Cells transfected with β-catenin alone, or with neither MAML3 nor β-catenin are shown as controls, in addition to the negative control FOP vector for every combination. Experiments was done three separate times in triplicate.


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Metastatic disease in pheochromocytomas and paragangliomas (PCC/PGL) is not well-understood. The Cancer Genome Atlas discovered recurrent MAML3 fusion genes in a subset of tumors that lacked known germline or somatic driver mutations and were associated with aggressive disease. Here, we aimed to investigate the role of MAML3 in tumorigenesis. Human PCC/PGLs were used for IHC and genetic analysis. Three neuroendocrine tumor cell lines, SK-N-SH, QGP-1, and BON-1, were transiently transfected with MAML3 (FL) or exon 1 deleted MAML3 (dEx1; mimicking the fusion), and biologic effects of overexpression were examined in vitro. We found 7% (4/55) of human PCC/PGL have UBTF∼MAML3 fusions and all were sporadic cases with metastatic disease. Fusion-positive tumors had intense MAML3 nuclear staining and increased β-catenin by IHC and showed increased WNT4 expression. In vitro, overexpression of FL and dEx1 MAML3 increased invasion in SK-N-SH, QGP-1, and BON-1 (all P < 0.05) and increased soft-agar colony formation in QGP-1 and BON-1 (all P < 0.05). Cotransfection with FL or dEx1 MAML3 and β-catenin increased TCF/LEF promoter activation by luciferase activity and coimmunoprecipitation confirmed interaction between MAML3 and β-catenin. These data suggest MAML3 is involved in WNT signaling pathway activation. In summary, UBTF∼MAML3 fusions are present in a subset of PCC/PGL and associated with metastatic disease without other known drivers. MAML3 overexpression led to increased tumorigenicity in neuroendocrine tumor cells and the mechanism of action may involve WNT signaling pathways. MAML3 increases tumorigenicity and invasion in neuroendocrine tumor cells and may be a prognostic marker for aggressive disease.

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