Link protein is ubiquitously expressed in non-cartilaginous tissues where it enhances and stabilizes the interaction of proteoglycans with hyaluronic acid.

Abstract

Link protein (LP) is an abundant protein of cartilage which stabilizes the interaction of aggrecan with hyaluronic acid (HA). In this study we report that LP is also present in a large number of embryonic non-cartilaginous tissues. We demonstrate, using RNase protection experiments, that the coding region of the LP mRNAs isolated from these tissues is identical to that present in cartilage. Furthermore, we show that the LP mRNAs are translated in non-cartilaginous tissues by the identification of LP polypeptides with monoclonal antibody 4B6/A5 in Western blots. LP is localized in the extracellular matrix of the mesoderm along the entire digestive tract and in the dermis of the embryonic skin as revealed by immunofluorescence analysis. Investigations on the interactions between LP and proteoglycans from skin and proventriculus demonstrate that LP can enhance the binding of proteoglycans from these tissues to HA. In addition, we find that the same proteoglycans bound to HA in the presence of LP are always more resistant to competition by soluble HA than in the absence of LP. Our results suggest that LP is involved in the stabilization of extracellular matrices of a wide variety of non-cartilaginous tissues.