Abstract 2948: HOXB13: Investigating mechanisms of G84E mutation associated with prostate carcinogenesis

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA In collaboration with Dr. K. Cooney's lab at the Univ of Michigan, our group recently discovered that a recurrent glycine-to-glutamic acid germline mutation (G84E) in HOXB13 is associated with an increased prostate cancer (PCa) risk. HOXB13 is an androgen receptor (AR)-independent prostate-specific transcription factor shown to play a critical role in the development of the mouse prostate. However, the exact function of HOXB13 in normal human prostate biology and the mechanism by which HOXB13 G84E predisposes carriers to PCa remain unknown. The purpose of this study is to test our hypothesis that HOXB13 G84E, by itself or together with other oncogenes, may reprogram normal prostate cells to be prone to transformation, possibly due to altered molecular characteristics that have downstream effects on transcriptional targets. To this end, using patient-derived normal prostate epithelial cells immortalized with hTERT in the presence or absence of transduced AR (957e/hTERT and 957e/hTERT/AR), we generated cell lines stably expressing HOXB13 WT or G84E to examine neoplastic phenotypes and differentiation. In the presence of AR, HOXB13 WT and G84E caused a change in cell morphology to a fibroblast-like appearance and suppressed proliferation without any significant differences between WT and G84E. In the absence of AR, the morphological and growth suppressive effects of HOXB13 were ablated, which indicates a cooperative relationship between HOXB13 and AR. In addition, we analyzed several molecular aspects of HOXB13 WT and G84E such as protein-interactions, subcellular localization and half-life which could hypothetically contribute to carcinogenesis when altered. Whether the HOXB13-MEIS and HOXB13-AR interactions are affected by G84E was studied for the following reasons. Most HOXB13 mutations identified in PCa lie in the MEIS-interacting domains (MID) of HOXB13 and the biological significance of HOX-MEIS complexes has been shown in leukemic transformation. HOXB13 mediates the transcription of a subset of AR-target genes and the HOXB13-AR interaction has been documented. Immunoprecipitation analysis in 957e/hTERT/AR demonstrated that HOXB13 and MEIS2 interact through the MIDs and G84E did not alter this interaction. Additionally, G84E did not disturb the HOXB13-AR interaction. Finally, HOXB13 G84E localized properly to the nucleus and no significant differences were found in the half-lives of HOXB13 WT and G84E, at least in the absence of AR. Taken together, our study suggests that HOXB13 G84E alone or with AR cannot initiate PCa in our cell line model with a caveat that our model does not accurately recapitulate human PCa since patients harbor the G84E mutation throughout development. Moreover, the lack of molecular differences between WT and G84E calls for further investigation of potential areas of G84E-induced alterations, such as gene-protein and protein-protein interactions on a global scale. Citation Format: Dorhyun Johng, Charles M. Ewing, Steven M. Mooney, Shuangling Chen, William B. Isaacs. HOXB13: Investigating mechanisms of G84E mutation associated with prostate carcinogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2948. doi:10.1158/1538-7445.AM2014-2948