Insulin-Like Growth Factors (IGF) and IGF-Binding Proteins Bound to Vitronectin Enhance Keratinocyte Protein Synthesis and Migration

The insulin-like growth factor (IGF) system plays an important role in a number of disease states, such as cancer and psoriasis, through its ability to modulate cell proliferation, attachment, and migration. The type-1 IGF and type-2 IGF receptors, as well as six IGF-binding proteins (IGFBP-1-6), have well-established roles in mediating IGF activity. Additionally, it's been demonstrated that IGF-II binds directly to the extracellular matrix protein vitronectin (VN), whereas IGF-I does not. IGFBP-5, however, has been recently demonstrated to facilitate the binding of IGF-I to VN. The aim of this study was to determine whether the interaction between IGF, IGFBP, and VN modulates human keratinocyte function. Functional assays demonstrated that both the IGF-II:VN and IGF-I:IGFBP-5:VN complexes resulted in significantly enhanced protein synthesis and cell migration through 12 microm pore Transwells in skin keratinocytes (HaCAT). Furthermore, the IGF-II:VN complex significantly enhanced human corneal epithelial (HCE) cell protein synthesis. Interestingly, the IGF-II:VN complex did not effect either HCE cell migration or attachment. This is the first study to demonstrate a functional role for the interaction between IGF and VN in human keratinocytes. Moreover, these results suggest that IGF-II:VN and IGF-I:IGFBP-5:VN complexes may be useful in situations where enhanced keratinocyte cell migration and proliferation is required, such as in wound healing and skin regeneration.