Sulfatase 2 protects hepatocellular carcinoma cells against apoptosis induced by the PI3K inhibitor LY294002 and ERK and JNK kinase inhibitors.

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide (1). Because of frequent de novo and acquired resistance of HCCs to chemotherapy, there are limited options for therapy of HCC (2, 3). There is therefore an urgent need for improved therapy of HCC. Consequently there is strong interest in identifying novel molecular targets for therapy of advanced HCC. The role of the extracellular heparan sulphate 6-O-endosulphatases, sulfatase 1 (SULF1) and sulfatase 2 (SULF2) in human carcinogenesis has not been completely elucidated (4, 5). SULF1 has been shown to function as a tumour suppressor in HCC, head and neck cancer, ovarian cancer and pancreatic cancer (5–10). SULF1 and SULF2 have also been reported to inhibit tumour growth in multiple myeloma (11). In contrast, SULF2 is upregulated in breast cancer and functions as an oncogene in HCC, pancreas cancer, lung cancer and chronic lymphocytic leukemia (12–16). Gene expression microarray analysis of 139 pairs of HCC tumour and adjacent benign tissue showed upregulation of SULF2 in 57% of HCCs (13). The 5-year survival rate for patients with HCCs with upregulated SULF2 was significantly worse than for those with down-regulated SULF2. Patients with upregulated SULF2 also had earlier recurrence of HCC after surgery. Immunohistochemical analysis of cell proliferation and apoptosis was performed in 30 of the HCCs (13). Tumours were classified into subclass A (poor prognosis) or subclass B (good prognosis) based on the prior gene expression profiling study by Lee et al. (17). Subclass A tumours were more frequent in the high SULF2 group (13 of 14 tumours) and less frequent in the low SULF2 group (two of 16 tumours; P=0.00001). HCCs with high SULF2 expression also had a significantly higher Ki-67 proliferation index (P= 0.007) and a significantly lower apoptosis index (P = 0.0001) than those with low SULF2 expression. SULF2 expression therefore correlated with increased proliferation and decreased apoptosis (13). In experiments to validate these results, we showed that SULF2 promoted proliferation and migration of HCC cells in vitro (13, 18). Mechanistically, SULF2 upregulated cell surface glypican 3 and promoted FGF signalling. Expression of SULF2 increased phosphorylation of Erk and Akt (13). SULF2 expression also increased phosphorylation of the anti-apoptotic Akt substrate GSK3β and stimulated Wnt/β-catenin signalling(19). Other investigators have also demonstrated that SULF2 promotes signalling by receptor tyrosine kinase ligands, Wnts and other growth factors (14, 20, 21). In terms of associations with other known pro-apoptotic molecules, SULF2 has been shown to be a transcriptional target of p53 in colon cancer, lung cancer, ovarian cancer and HCC cells, but the direct or indirect effects of SULF2 on apoptosis and apoptosis-related pathways in HCC have not been reported (22, 23). ERK, PI3K/Akt and JNK pathway inhibitors and histone deacetylase (HDAC) inhibitors induce apoptosis and are currently in clinical trials for cancer therapy (24–26). We studied the expression of SULF2 in HCCs and determined the role of SULF2 in modulating apoptosis induced by these kinase and HDAC inhibitors in HCC cells. The questions addressed in this study were: Is SULF2 mRNA expression correlated to protein expression in HCCs? Do changes in SULF2 expression affect cell viability, caspase activation and induction of apoptosis of HCC cells by ERK, PI3K, JNK or HDAC inhibitors? Does knockdown of SULF2 inactivate the Akt pathway? Does knockdown of SULF2 inhibit cell cycle progression as measured by cyclin D1 expression? Does SULF2 mediate its effects by regulating apoptosis-related Bcl-2, Bcl-XL and BAD protein expression?