The functional consequences of the interactions between insulin-like growth factors (IGFs), insulin-like growth factor binding proteins (IGFBPs) and vitronectin (VN) and their involvement in skin

The insulin-like growth factor (IGF) system plays an important role in a number of disease states, such as cancer, and has also been implicated in wound and burn healing processes. Two IGF receptors, the type-1 IGF and type-2 IGF receptors, as well as six insulin-like growth factor binding proteins (IGFBP-1 to 6), have well established roles in mediating IGF activity. Earlier studies in this laboratory demonstrated that IGF-II binds to the extracellular matrix (ECM) protein vitronectin (VN), and although IGF-I does not bind directly to VN it can bind indirectly via specific IGFBPs. Therefore the aim of the research described in this thesis was to determine whether binary and ternary complexes of IGF-I/II, IGFBPs and VN affect human keratinocyte cell function. The strategy of pre-binding these complexes to the culture dishes was adopted in this study in an attempt to more accurately reflect the extracellular environment in vivo. These studies demonstrated that the binary complex of IGF-II and VN and the ternary complexes comprised of IGF-I, IGFBP-2, or 3, or 4, or 5 and VN significantly stimulated HaCaT de novo cell protein synthesis in the human keratinocyte cell line. Interestingly, these latter experiments demonstrated that although large increases in protein synthesis were observed using the ternary complexes, IGF-I/IGFBP complexes alone were responsible for the significant increases in protein synthesis and these responses are mediated via the MAPK signaling pathway. In addition, both the dimeric and trimeric complexes significantly enhanced cell migration through 12 μm TranswellsTM. Unlike the protein synthesis assays, VN was critically important in these migratory responses and highlighting the important role that integrins play in cell migration. Cell attachment assays on the other hand demonstrated that the interactions of IGFs with IGFBPs and VN did not affect cell attachment. The data encompassed within this thesis represent the first studies to provide a functional role for the interaction between IGFs, IGFBPs and VN in human keratinocytes. Taken together these results suggest that IGF/IGFBP/VN complexes may hold great potential in situations where enhanced keratinocyte cell migration and proliferation is required, such as in wound healing and skin engineering applications