The role of HPSE in BRAF V600E-mutant colorectal cancer.

Abstract

3530 Background: BRAF mutations occur in about 10% of colorectal cancer (CRC), more than 90% of which are BRAF V600E mutation. Patients (pts) with BRAF V600E mutation present poor prognosis. Complex molecular biological mechanisms in this population have not been well annotated. HPSE plays a multifunctional role in cell proliferation, invasion and angiogenesis in cancer. Here we identified differentially expressed genes (DEGs) between pts with and without BRAF V600E mutation, and then focused on the function of HPSE, one of top DEGs, in BRAF V600E-mutant CRC. Methods: Clinical and transcriptional data of pts with CRC from The Cancer Genome Atlas (TCGA, n = 525) database and GSE39582 dataset (n = 510) were analyzed to explore the top overlapped DEGs between BRAF V600E mutant and wild-type pts. Records and tumor samples of 172 pts with BRAF V600E-mutant CRC diagnosed at Zhongshan Hospital Fudan University between 6/2015-12/2018 were collected. The HPSE protein expression status of tumor samples was evaluated by immunohistochemistry staining. Moderate or strong staining in > 25% of tumor cells was interpreted as HPSE positive. Overall survival (OS) was analyzed using Kaplan-Meier Curves with Log-rank test and multivariable Cox regression. Next, lentiviral shRNA-based silencing of HPSE was performed in two BRAF V600E-mutant CRC cell lines (HT-29, RKO). The effect of HPSE on tumor growth was investigated through colony formation assays, cell cycle assays and subcutaneous xenograft models. Results: The top overlapped genes of the DEGs list included HPSE, TFF2, AXIN2, MLH1, RNF43, EPM2AIP1. Among them, HPSE had significantly high expression in BRAF V600E-mutant group. Of 172 pts with BRAF V600E mutation, 83 were identified as HPSE positive and 89 were negative. Two groups were generally well balanced on age (p = 0.096), gender (p = 1.000), location (p = 0.658), stage (p = 0.249) and MMR status (p = 0.129). HPSE positive pts had a significantly worse OS in comparison to HPSE negative pts (p = 0.037, median OS not reached). The multivariate analysis showed that HPSE positive was independently associated with inferior OS [HR 1.97 (95%CI: 1.02 – 3.80), p = 0.044). Silencing HPSE gene impaired colony formation activity significantly and arrested more cells in G0/G1 phase of BRAF V600E-mutant CRC cell lines. Tumor growth was inhibited apparently in HPSE-silencing xenograft models. Conclusions: Pts with BRAF V600E-mutant CRC had a high HPSE expression level, while HPSE protein expression was an independent prognostic factor for this population. The silencing of HPSE expression in BRAF V600E-mutant CRC cell lines inhibited cell proliferation and tumor growth in vitro and in vivo. HPSE may contribute to the poor prognosis of BRAF V600E-mutant CRC and might be a promising therapeutic target for this subtype of CRC.