Purification and characterization of recombinant heparanase 2

Abstract

On mammalian cell surface, the role of extracellular matrix (ECM) is found to be crucial in providing structural support to cells. In addition, the ECM confers barrier property to nearby tissues and serves as a platform for growth factor binding and cell signaling from the extracellular to the intracellular environment. In developing as well as cancer tissue, modulation of the ECM regulates cell emigration versus homing. The ECM has also been implicated in the regulation of synaptic plasticity. The ECM is composed of a supramolecular array of proteoglycans and glycoproteins. Such a complex structure can be categorized according to function and/or structural components. In fact, the ECM is a dynamic structure in which the abundance and components are subject to change so as to meet physiological needs of cells and such modulation is usually accomplished via enzymes. In this dissertation, we focus on one of the ECM components, heparan sulfate (HS) proteoglycans and the HS-binding protein, heparanase 2, which show homology to heparanase 1 but lack HS-cleaving enzyme activity. Clinical and biochemical research studies have already proved that the heparanase 2 protein can attenuate the growth of cancer cells and tumor metastasis but the exact underlying mechanism remains unclear . It is hypothesized that it competes with its homolog heparanase 1 for binding to HS. When the HS binding sites are occupied by heparanase 2, enzymatic cleavage of the HS by heparanase 1 would be limited so that metastatic migration of cancer cells could be inhibited. However, this hypothesis is yet to be confirmed and some clinical studies of certain types of cancer have reported that the inhibition of cancer metastasis by heparanase 2 have no direct relation with heparanase 1 . Results from our lab have also proposed a model that the synaptic strength could be modulated through pro-heparanase /HSPG clustering of AMPAR in the peri-synapse resulting in AMPAR internalization. It is therefore to our interest to find if heparanase 2 also plays a role in such synaptic plasticity and if so, how this occurs. To address this, recombinant heparanase 2 protein was prepared and purified. With use of the recombinant protein preparation, this study demonstrated the binding affinity of heparanase 2 was stronger than its homolog heparanase 1 but heparanase 2 lacked HS-cleaving enzyme activity. This paves the way for further studies on the role of heparanase 2 in synaptic plasticity.