Abstract 1637: EPHB4 is a key regulator of G1/S transition in hepatocellular carcinoma

Abstract

Abstract Effective therapeutic regimens against advanced hepatocellular carcinoma (HCCs) have recently improved but it remains very limited. Targeting receptor tyrosine kinases (RTKs) has proven to one of the main ways of achieving better survival outcome in HCC patients, yet the precise mechanism for this success remains to be elusive. We have systematically investigated the expression profiles of RTKs transcriptomic datasets i.e. The Cancer Genome Atlas - Liver hepatocellular carcinoma (TCGA-LIHC) (n=371) and our in-house cohort of paired i.e. HKU-QMH (n=41), and identified EPHB4 as one of the most abundantly expressed and frequently mutated RTKs in human HCCs. EPHB4 expression was found to be significantly correlated with Alpha Fetoprotein (AFP) expression, a factor commonly used in the diagnosis of HCCs. Furthermore, EphB4 has been demonstrated to play a regulatory role in VEGF/VEGFR-mediated angiogenesis, critical targets for current successful drugs. We confirmed abundant membrane EphB4 expression in HCC clinical specimens and human HCC cell line models using immunohistochemistry. Clinicopathological correlation analysis of EPHB4 mRNA expression revealed that its overexpression is associated with aggressive tumor features including presence of tumor microsatellite, liver invasion, venous invasion, and absence of tumor encapsulation. Functionally, stably knocking down EPHB4 (shEPHB4) resulted in a strong reduction of proliferation and self-renewal rates of multiple HCC cell lines in vitro. It significantly reduced tumor growth rates in subcutaneous and liver orthotopic models in vivo. Furthermore, limiting dilution assay showed EPHB4 plays a role in tumor initiation property of HCC cells. Mechanistically, we performed Gene Set Enrichment Analysis (GSEA) of transcriptome profiles for shEPHB4 with respective controls and found that knocking down EPHB4 causes HCC cells undergo drastic changes in several cell cycle checkpoints including G1/S transition. Using thymidine blockade, we further confirmed that knockdown of significantly hinders the transition of HCC cells from G1 to S phase of cell cycle. Our data suggests a strong link between EphB4 and cell cycle. Conclusion: We found EphB4 plays a functional role in regulating G1/S transition in human HCCs and understanding regulatory role of EphB4 on cell cycle progression may provide mechanistic insights into the how to effectively target HCC in the clinic. Citation Format: Abdullah Husain, Elley Y. Chiu, Hoi-Tang Ma, Daniel W. Ho, Karen M. Sze, Lo-Kong Chan, Irene O. Ng. EPHB4 is a key regulator of G1/S transition in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1637.