The involvement of the NF-κB pathway in the HOXA1 : ERα antagonism in breast cancer

Details

Supervisors

Rezsohazy, René ; Morsomme, Pierre

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries

Abstract

Breast cancer, the most frequent type of cancer among women, results from the uncontrolled growth of cells in breast tissue. This proliferation is caused by various mechanisms and genes among which are the Hox gene family. Hox genes code for transcription factors fundamentally involved in regulating animal embryogenesis. However, they can be expressed throughout postnatal life and their mutation or mis-regulation is linked to the onset or progression of cancer. Hoxa1, a member of the Hox family, has been linked to several cancer types including breast cancer. Clinical datasets have revealed the abnormal activation of Hoxa1 in breast cancer patients. Consistently, models demonstrated that forced expression of HOXA1 in human mammary epithelial cells leads to their oncogenic transformation into aggressive carcinomas. Moreover, a recent study has revealed the interaction between HOXA1 and signaling pathways leading to the activation of NF-κB, an oncoprotein. Strikingly, Hoxa1 expression and activity of the NF-κB pathway are strongly correlated in breast tumors. Besides, preliminary results from the host laboratory support the existence of a functional antagonism between HOXA1 and ERα, a third oncoprotein. Finally, studies suggest that in certain breast cancer models, ERα and NF-κB display cross repressive activities. The possible cross regulatory influences between proteins which are all identified as breast oncoproteins stress the fact that the etiology of breast cancer is diverse and heterogeneous. The general objective of our work was to contribute to characterize the molecular and functional interaction between HOXA1 and ERα. A first objective was to identify the ERα domains involved in the interaction with HOXA1. The molecular interaction between HOXA1 and ERα has been previously observed in the lab. ERα variant derivatives have been generated and we identified one N-terminal domain of ERα which is essential to the interaction and two other protein regions possibly involved in modulating this interaction. A second objective was to investigate the possible involvement of NF-κB in the HOXA1 – ERα antagonism. In that regard we identified a reliable inhibitor of the NF-κB pathway and revealed that HOXA1 inhibits ERα transcriptional activity through NF-κB. To investigate the mechanisms this inhibition, we measured the abundance in ERα with or without HOXA1 as well as upon NF-κB inhibition, but the results did not support that changes in ERα abundance could correlate to the activity changes observed. Third, the PBX protein has been identified as a molecular and functional interactor of HOXA1 and ERα. In that context, the HOXA1 – ERα antagonism might result from their competition for PBX. We aimed at studying the impact of PBX on the transcriptional activity of the oncoproteins under study and highlighted that PBX could increase the activity of both ERα and HOXA1. Finally, to translate the HOXA1 – ERα antagonism in terms of cellular response, we aimed at developing a foci formation assay to observe the influence of HOXA1, ERα and NF-κB, on the oncogenic potential of breast cell lines. Although the assay still requires adjustments, our results showed that PBX sustains foci formation. In conclusion, our work provides new insights into the involvement of NF-κB in the HOXA1–ERα antagonism as well as into the contribution of PBX to these complex interactions taking place in the context of breast cancer.