Hpa2 Gene Cloning.

From 1999-2003, Oxford GlycoSciences (OGS) ran a successful drug discovery oncology programme to discover small molecule inhibitors of the Heparanase I enzyme (HPSE1). HPSE1 at the time was widely regarded as being the sole mammalian enzyme capable of cleaving Heparan Sulfate (HS). A second family protein member however called Heparanase 2 (HPSE2) including splice forms was subsequently discovered by PCR analysis based on EST sequences. HPSE2 was found to be expressed mainly in smooth muscle containing tissues, particularly bladder and brain. HPSE2 is poorly expressed in haematopoietic cells and placenta which contrasts with the HPSE1 distribution pattern. HPSE2 binds more strongly to HS than HPSE1 and is believed to out compete for substrate binding and so in effect act as a tumor suppressor. So far, all attempts to show specific HPSE2 endoglycosidase activity against HS have failed suggesting that the enzyme may act as a pseudoenzyme that has evolved to retain only certain non-catalytic heparanase like functions. A breakthrough in the elucidation of functional roles for HPSE2 came about in 2010 with the linkage of HPSE2 gene deletions and mutations to the development of Ochoa/Urofacial Syndrome. Future work into the mechanistic analysis of HPSE2's role in signalling, tumor suppression and bladder/nerve functioning are needed to fully explore the role of this family of proteins.

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