The many facets of heparanase : not just an extracellular matrix-degrading enzyme

Abstract

Heparanase is an endo-{u03B2}-glucuronidase that cleaves heparan sulfate and facilitates the passage of migrating cells through extracellular matrices (ECM), particularly basement membranes, as well as releasing heparan sulfate-bound growth factors from the ECM, whereby the released growth factors also aid wound healing and angiogenesis. Under normal physiological conditions heparanase aids the passage of leukocytes through subendothelial basement membranes and entry into sites of inflammation. It is also well established that heparanase, via a similar mechanism, plays a critical role in the metastatic spread of cancer. Recent studies have suggested, however, that heparanase has biological functions independent of its enzymatic activity. A number of studies have also reported the presence of beparanase in the nucleus of cells, with nuclear heparanase being associated with a favourable prognosis and cytoplasmic beparanase with poor survival in patients with lung, neck and gastric cancers. There is some evidence that nuclear heparanase expression is linked to cancer cell differentiation but, despite such reports, the functional relevance of nuclear heparanase remains to be established. This thesis describes experiments which demonstrate that nuclear heparanase can regulate transcription in resting and activated human T lymphocytes. Initial immunofluorescence studies revealed that nuclear heparanase is associated with euchromatin, and not heterochromatin, in both resting and activated human T cells. Subsequent single locus ChIP as well as genome wide ChIP-on-chip analysis, identified a cohort of immune-related target genes that are bound by heparanase at their promoter and coding regions. Additional knockdown and over-expression experiments showed that chromatin-tethered heparanase is required for the inducible transcription of several of these genes in activated T cells. In fact, at the chromatin level, it was found that heparanase regulates histone H3K4 and H3K9 methylation, probably by binding to target gene control regions in association with the demethylase LSD1. It has been further shown that association of heparanase with the LSD1 complex is accompanied by a lack of recruitment of the methylase, MLL, suggesting that heparanase plays a central role in mediating the on/off switch of inducible gene transcription. Taken together, these data suggest a hitherto unanticipated role for nuclear heparanase as a novel chromatin-associated regulator of transcription in mammalian cells. Show more