41 - The Role of cad6b Long N-terminal Fragments in Matrix Metalloproteinase Activation During the Cranial Neural Crest Cell Epithelial-to-mesenchymal Transition

Poster Board Number: 41
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Co-authors:

Lisa Taneyhill - Principal Investigator, Animal Sciences, University of Maryland

Abstract Body : Neural crest cells (NCCs) give rise to diverse structures such as the craniofacial skeleton, melanocytes, and sensory ganglia. Because of the contributions of NCCs to these different cell types, aberrant NCC development can lead to various neurocristopathies, many of which are fatal and have no form of treatment. Stationary premigratory NCCs undergo a hallmark epithelial-to-mesenchymal transition (EMT) early in development in which they delaminate from the neural folds, adopt a mesenchymal morphology, and begin to migrate throughout the embryo. Mechanisms controlling NCC delamination and EMT are crucial to uncover since EMT is hijacked by cancer cells during metastasis and underlies diseases like fibrosis. To this end, our lab has demonstrated the importance of modulating cadherin-based adhesion in premigratory NCCs during EMT. Our prior studies revealed that chick premigratory cranial NCCs express and later downregulate Cadherin-6B (Cad6B) through proteolytic processing to promote NCC EMT. This proteolysis generates long and short extracellular Cad6B N-terminal fragments (L- and S-NTFs, respectively) and intracellular Cad6B C-terminal fragments. Moreover, Cad6B L-NTFs promote NCC delamination and EMT, in part, by increasing matrix metalloproteinase 2 (MMP2) activity. This leads to further proteolysis of Cad6B by MMP2 and enhances degradation of proteins within the dorsal neural tube basement membrane, facilitating early NCC migration. Additionally, active MMP2 is generated by proMMP2 proteolysis, which is mediated by other MMPs like MMP16, further highlighting the importance of MMPs in facilitating NCC EMT. However, the function and mechanism of action of Cad6B L-NTFs in directing NCC EMT via MMPs remains to be characterized. Our preliminary results now show that both proMMP2 and MMP16 physically interact with Cad6B L-NTFs in vivo, providing a potential molecular mechanism for the observed increase in MMP2 activity. Given our current findings, we hypothesize that Cad6B L-NTF activation of MMP2 requires formation of a Cad6B L-NTF-proMMP2-MMP16 complex and is dependent upon MMP16 activity, thereby promoting NCC EMT. To address this hypothesis, we will define the nature of the interaction among Cad6B L-NTFs and MMPs by performing molecular perturbation assays, biochemistry, and proximity ligation during NCC EMT. Future experiments will explore whether MMP16 is required for L-NTF-mediated activation of MMP2 and possesses catalytic-independent functions to direct NCC EMT. Collectively, our results will provide insight into the molecular mechanisms by which Cad6B L-NTFs drive NCC EMT, contributing to our understanding of craniofacial development and the diseases that ensue upon abnormal NCC development. This work is funded by NSF IOS-1947169 (L.A.T.).