Abstract The neurodevelopmental transcription factor POU3F2 (also called OCT7 / BRN2) is expressed during neurogenesis. Moreover, POU3F2 expression has been reported as a promoter of proliferation and invasion in malignant melanoma of the skin. Since both melanomas and CNS-malignancies arise in organs of neuro-ectodermal origin, we investigated whether human gliomas expressed POU3F2 and the role of POU3F2 in glioma tumorigenesis. We performed immunohistochemistry of 149 grade II-IV gliomas from our tumor bank, and subsequently performed western blots and qPCR of 12 samples from each grade. In addition, we performed flow cytometric analysis of POU3F2 expression in 5 acutely dissociated tumors. Using lentiviral transfection we established glioma cell lines with POU3F2 overexpression or knock down in order the to investigate the effect of POU3F2 on proliferation, migration and differentiation, both in vitro and in vivo. The mechanism, by which POU3F2 regulates glioma progression, was also investigated. Immunohistochemistry showed that POU3F2 was almost uniformly expressed in human gliomas. Both western blot, qPCR and flow cytometry confirmed expression of POU3F2 in human gliomas. In acutely dissociated tumors, the POU3F2 positive cells displayed an increased cell percentage in the S and G2/M phase of the cell cycle. Moreover, POU3F2 overexpression in the glioma cell lines increased growth rates and colony formation. Overexpression of POU3F2 increased the levels of phosphorylated p-44/42 indicating activation of the ERK1/2 signaling pathway. Increased levels of downstream transcriptional targets c-Myc, Elk1 and Stat3 transcription factors in the POU3F2 overexpressing cell lines confirmed activation of the MAPK signaling pathway. Furthermore, the POU3F2 overexpressing cell lines displayed increased expression of the growth factor FGF2. U0126, an inhibitor of MEK1/2, decreased the cell proliferation and decrease levels of phospho-p44/42, phospho-stat3 and FGF2. Moreover, overexpression of the POU3F2 increases the level of other neurodevelopmental transcription factors associated with a pluripotent state. Ongoing studies aim at further elucidating the multiple roles of POU3F2 in brain tumor progression. Citation Format: Mohummad Aminur Rahman, Lina Liess, Mohammad S. Lellahi, Christiane H. Gjerde, Halala S. Saed, Ercan Mutlu, Huaiyang Zhu, Jian Wang, Per Øyvind Enger. The transcription factor POU3F2 is expressed in human gliomas and promotes tumorigenesis in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2101. doi:10.1158/1538-7445.AM2015-2101