Numerous signalling pathways control the cellular processes mediating cancer growth and metastasis. Wnt- and integrin-mediated signalling play important roles in these processes, and as such, targeting these pathways has been considered for the development of potential cancer therapeutics.
Secreted Frizzled-related protein 4 (sFRP4) is an endogenous protein well-known as a Wnt signalling antagonist.1 sFRP4 consists of two domains: a Frizzled-type cysteine-rich domain (CRD) and a netrin-like domain (NLD). The CRD is the likely domain responsible for Wnt signalling inhibition, due to its similarity to the CRD of the Frizzled receptor; sFRP4 CRD binding to Wnt proteins would prevent Wnt binding to Frizzled, thus prevent Wnt signal transduction. Although the NLD appears to have a role in attentuating cancer growth and spread, the molecular mechanism by which it achieves this remains elusive. It has previously been reported that TIMP-2, canonically a matrix metalloproteinase inhibitor, is also capable of blocking angiogenesis via antagonising integrin signaling, by direct binding to integrin;2 TIMP-2, like the NLD of sFRP4, folds as a netrin-like domain. Therefore, due to this fold similarity, we hypothesise that the sFRP4 NLD may be acting as an integrin antagonist to mediate its biological function.
In this study, we have investigated the structural basis of TIMP-2 and sFRP4 NLD binding to integrin α3β1. A combination of molecular docking, homology modelling and loop resampling was used to propose a TIMP-2-integrin complex, which informed modelling of an sFRP4 NLD complex with integrin α3β1. Steered molecular dynamics simulations applying constant force to the integrin headpiece suggest that the sFRP4 NLD may afford improved integrin antagonism compared to TIMP-2, thus illustrating its potential to act as an integrin antagonist. The knowledge derived from this study will inform the development of sFRP4-based cancer therapeutics.