Perlecan, a modular instructive proteoglycan with diverse functional properties.

This study reviewed some new aspects of the modular proteoglycan perlecan, a colossal proteoglycan with a 467 kDa core protein and five distinct functional domains. Perlecan is a heparan sulphate proteoglycan that transiently displays native CS sulphation motifs 4-C-3 and 7-D-4 during tissue morphogenesis these are expressed by progenitor cell populations during tissue development. Perlecan is susceptible to fragmentation by proteases during tissue development and in pathological tissues particularly in domains IV and V. The fragmentation pattern of domain IV has been suggested as a means of grading prostate cancer. Domain V of perlecan is of interest due to its interactive properties with integrin α5β1 that promotes pericyte migration enhancing PDGF-BB-induced phosphorylation of PDGFRβ, Src homology region 2 domain-containing phosphatase-2, and focal adhesion kinase supporting the repair of the blood brain barrier following ischaemic stroke. Fragments of domain V can also interact with α2β1 integrin disrupting tube formation by endothelial cells. LG1-LG2, LG3 fragments can antagonise VEGFR2, and α2β1 integrin interactions preventing angiogenesis by endothelial cells. These domain V fragments are of interest as potential anti-tumour agents. Perlecan attached to the luminal surfaces of endothelial cells in blood vessels acts as a flow sensor that signals back to endothelial and smooth muscle cells to regulate vascular tone and blood pressure. Perlecan also acts as a flow sensor in the lacuno-canalicular space regulating osteocytes and bone homeostasis. Along with its biomechanical regulatory properties in cartilaginous tissues this further extends the functional repertoire of this amazingly diverse functional proteoglycan.