Expression pattern and secretion of human and chicken heparanase are determined by their signal peptide sequence

Cleavage of heparan sulfate (HS) proteoglycans affects the integrity and fu nction of tissues and thereby fundamental phenomena, involving cell migrati on and response to changes in the extracellular microenvironment. The role of HS-degrading enzymes, commonly referred to as heparanases, in normal dev elopment has not been identified. The present study focuses on cloning, exp ression, and properties of a chicken heparanase and its distribution in the developing chicken embryo. We have identified a chicken EST, homologous to the recently cloned human heparanase, to clone and express a functional ch icken heparanase, 60% homologous to the human enzyme. The full-length chick en heparanase cDNA encodes a 60-kDa proenzyme that is processed at the N te rminus into a 45-kDa highly active enzyme. The most prominent difference be tween the chicken and human enzymes resides in the predicted signal peptide sequence, apparently accounting for the chicken heparanase being readily s ecreted and localized in close proximity to the cell surface. In contrast, the human enzyme is mostly intracellular, localized in perinuclear granules . Cells transfected with a chimeric construct composed of the chicken signa l peptide preceding the human heparanase exhibited cell surface localizatio n and secretion of heparanase, similar to cells transfected with the full-l ength chicken enzyme. We examined the distribution pattern of the heparanas e enzyme in the developing chicken embryo. Both the chicken heparanase mRNA and protein were expressed, as early as 12 h post fertilization, in cells migrating from the epiblast and forming the hypoblast layer. Later on (72 h ), the enzyme is preferentially expressed in cells of the developing vascul ar and nervous systems. Cloning and characterization of heparanase, the fir st and single functional vertebrate HS-degrading enzyme, may lead to identi fication of other glycosaminoglycan degrading enzymes, toward elucidation o f their significance in normal and pathological processes.