Characterization of HOXA1-mediated inhibition of canonical Wnt signaling

HOXA1 is one of the 39 known HOX proteins expressed in humans and mice. Being among the earliest and most anteriorly expressed HOX genes, the HOXA1 gene codes for a homeodomain transcription factor that will act as a master regulator for several developmental processes which play major roles in hindbrain segmentation and neural crest development. As with several other HOX genes, HOXA1 has also been observed to play the part as an oncogene when abnormally expressed in adult tissues and is hypothesized to play a major role in the onset of aggressive, therapy-resistant forms of breast cancer. The Wnt/β-catenin signaling pathway (also known as the “canonical” Wnt pathway) is a major developmental signaling cascade that relies on the Wnt-mediated inhibition of β-catenin degradation to activate the transcriptional response associated with the pathway. Wnt signaling is known to play a major role during embryo development in almost every organ and tissue of the developing organism, and its abnormal activation in the adult has been linked to oncogenesis and cancer progression. Previous preliminary results obtained in vitro in the context of studying the involvement of mutant forms of HOXA1 in developmental abnormalities of certain neural crest-derived structures have suggested that HOXA1 and the canonical Wnt/β-catenin pathway are capable of interacting, with HOXA1 having a possible inhibitory effect on the pathway. Due to the shared biological contexts in which HOXA1 and the canonical Wnt pathway act, we consider that this observed inhibition may play an important role in both embryo development and cancer. For this master thesis, we attempted to further characterize the nature of this observed inhibition. To do this, we proceeded with several tests designed to assay Wnt pathway transcriptional effects in the presence or absence of HOXA1, using transcriptional reporter assays or by quantification of the endogenous expression of Wnt target genes. Concomitantly, we also attempted to visualize β-catenin concentrations in the cell, as variations of β-catenin can also be indicative of canonical Wnt pathway activation or inhibition. The results presented in this master thesis are thus one first attempt to explore this previously uncharacterized interaction between HOXA1 and the Wnt/β-catenin signaling pathway in vitro, using molecular biology approaches to understand the precise effects of HOXA1 on the Wnt pathway.