Serine peptidase inhibitor, Kazal type 1 (SPINK1) as a novel effector of cadherin-17 (CDH 17)/beta-catenin axis in hepatocellular carcinoma

Abstract

Liver cancer is the fifth most commonly diagnosed and the second most lethal malignancies worldwide, in which hepatocellular carcinoma (HCC) represents the majority subtype. High mortality rate of HCC is due to lack of effective treatments and early detection methods. Activation of cadherin-17 (CDH17)/β-catenin axis is found by our team in HCC and targeting components of this axis associated with anti-tumorigenesis. With limited knowledge on this axis in HCC, I plan to study molecules related to this axis as a way to uncover the cellular mechanism of this axis in liver tumorigenesis. Gene profiling data was re-analyzed to search for CDH17-associated genes in HCC clinical samples. The patient cohort was segregated into CDH17-high and CDH17-low group according to tumor/adjacent non-tumor expression ratio of CDH17. Serine peptidase inhibitor, Kazal type 1 (SPINK1) was found highly expressed in CDH17-high cases and its over-expression accounted for 73 % of total studied cases. Gene manipulation and inhibitor study in HCC cell lines suggested SPINK1 as a downstream molecule of CDH17/β-catenin axis in HCC. Further in silico analysis predicted potential binding sites of two transcriptional factors downstream of CDH17/β-catenin axis, lymphoid enhancer-binding factor 1 (LEF1) and T-cell factor 7 (TCF7), on SPINK1 promoter. Deletion or mutation of their binding sites on SPINK1 promoter suppressed the transcription of SPINK1 gene, while transient suppression of these two transcriptional factors resulted in reduction of SPINK1 level. As the direct link between SPINK1 and CDH17/β-catenin axis was confirmed, SPINK1 was hypothesized to possess tumorigenic properties like its upstream molecule CDH17. Suppression of SPINK1 using RNA interference in PLC and MHCC97-H HCC cells hampered growth, migration and colony formation abilities of suppressed cells. These phenotypic alterations accompanied with an inactivation of tumorigenic c-Raf/MEK/ERK pathway. These findings demonstrate the tumorigenic properties of SPINK1 in HCC. Next, the therapeutic potential of targeting SPINK1 in HCC was tested by using purified monoclonal antibody raised against recombinant SPINK1 protein (C4). C4 was capable in suppressing SPINK1 level based on results of immunocytochemisty, enzyme-linked immunosorbent assay and immunoneutralization. Treatment of HCC cells using C4 suppressed growth, migration and colony formation ability of cells by inactivating MAPK pathway. In subcutaneous tumor xenograft study, treating tumor-bearing mice with C4 at 8 mg/kg three times weekly inhibited tumor growth by around 65 %. These findings demonstrate C4 is a potential therapeutic for counteracting liver tumorigenesis.

In conclusion, I have demonstrated for the first time SPINK1 as a novel downstream molecule of CDH17/β-catenin axis involved in HCC progression via activating MAPK pathway. Targeting this molecule with its specific monoclonal antibody is a potential approach for cancer therapy.