Elucidating the role of Heparanase-2 (Hpa2) in pancreatic cancer

Introduction. Heparanase is an endoglycosidase that specifically cleaves heparan sulfate (HS) side chains of proteoglycans that are abundantly present in the extracellular matrix (ECM) and on the cell surface. Heparanase activity is strongly implicated in tumor angiogenesis and metastasis attributed to remodeling of the subepithelial and subendothelial basement membranes. Heparanase 2 (Hpa2) is a close homolog of heparanase that lacks intrinsic HS-degrading activity but retains the capacity to bind HS with high affinity, thus competing for HS binding and inhibiting heparanase enzymatic activity. In head and neck cancer patients, Hpa2 expression was markedly elevated, correlating with prolonged time to disease recurrence and inversely correlating with tumor cell dissemination to regional lymph nodes, suggesting that Hpa2 functions as a tumor suppressor. The molecular mechanism associated with favorable prognosis following Hpa2 induction is unclear. Hpa2 nonetheless appears to down-regulate the expression pro-angiogenic genes (i.e., VEGF-A, VEGF-C) and to promote cell differentiation (i.e., E-cadherin, cytokeratins). Here, we examine the role of Hpa2 in pancreatic cancer.

Materials and methods. Human pancreatic tumor biopsies were subjected to immunostaining for Hpa2 and the immunostaining intensity was correlated to the clinical record of patient. Control (Vo) and Hpa2 over-expressing pancreatic carcinoma cell lines (i.e., Panc01, MiaPaca, Capan, AsPC, BxPC3), were examined for their tumorigenic capacity. Luciferase-labelled cells were inoculated sub-cutaneously, intra-peritonealy, and orthotopically and tumor growth was followed by IVIS. We further examined Hpa2 mode of action as a tumor suppressor in pancreatic cancer, focusing on angiogenesis, lymph-angiogenesis, tumor fibrosis and ER-stress.

Results. Hpa2 was not detected in normal pancreatic ducts was its expression was noticeably increased in some pancreatic ductal adenocarcinoma. Notably, patients stained positively for Hpa2 survived longer that Hpa2-negative patients. Hpa2 over expression inhibited pancreatic tumor growth in different in-vivo models, and the Hpa2 over expressing tumors showed an increased level of ER-stress (i.e., Bip, CHOPS, pPERK, peIF2), likely leading to apoptotic cell death. Interestingly, ER-stress and hypoxic, each alone and in combination induced Hpa2 expression in several pancreatic cancer cell lines. Taken together, a feed-back cycle seems to persist, leading to continuous cell stress, leading to reduced tumor growth.

Conclusions. Different in-vivo models results suggest that Hpa2 functions as a tumor suppressor. In addition, both in-vivo and in-vitro experiments indicate that Hpa2 elicit ER-stress, thus providing a novel mechanism by which Hpa2 restrain tumor growth.