Abstract 1311: PCSK9 expression in liver sinusoidal endothelial cells during liver metastasis
Authors: Sebastian Ander Martin-San , García-García Helena , Siegfried Géraldine , Khatib Abdel-Majid , Badiola Iker 
Published: April 2023

Abstract
PCSK9 is a serin protein kinase of the family of convertases. It has been extensively studied in hypercholesterolaemia, but has recently been shown to be involved in cancer. It is overexpressed in several types of cancer, especially during the process of metastasis. One of the most common is colon liver metastasis. In this process of dissemination, the tumor microenvironment plays a key role. Our research focuses on the function of PCSK9 in liver sinusoidal endothelial cells (LSECs) involved in angiogenesis. We have shown in a study in vitro by qPCR and western blotting (WB), that PCSK9 protein is expressed in LSECs under basal conditions. Furthermore, we activated the cells with media from SW620 tumor cells as well as from SW620-derived cancer stem cells (CSCs) during 24 hours. Thus, we have shown that activation of LSECs with CSC conditioned media significantly increases PCSK9 expression at the mRNA level. This is the first time this convertase is detected in LSECs. In addition, we performed an immunofluorescence (IF) staining of PCSK9 to determine the cellular localization of the protein in this cell type. We found PCSK9 in the nucleus of LSECs in cell culture. Furthermore, we have confirmed the nuclear location by a WB analysis of the cytoplasmatic and nuclear fraction of the cells. As far as we know, this localization of PCSK9 has never been observed which open the possibility of new function for PCSK9 in LSECs. In addition, we performed IF staining in human tissues, both adjacent and metastatic livers. Thus, LSECs were labelled with the specific marker CD31 and PCSK9 demonstrating that PSCK9 is also expressed in patient’s LSECs. Regarding cellular localization, the protein appears to be localized in the nucleus according to the observations made in vitro. In order to determine PCSK9 function, we overexpressed PCSK9 in HEK cells and we co-immunoprecipitated it to study the related proteins. Some protein of interest appeared as far as EpCAM and CDK6 which are being studied. Furthermore, we inhibited PCSK9 with siRNA and chemical inhibitor (PF-06446846). We performed a proliferation test in both conditions and we showed that LSEC proliferation significantly decrease when we inhibit PCSK9. Finally, we did a RNAseq study in LSEC cells inhibiting PCSK9 after their activation with CSC media. This result showed us a significant decrease expression of ERN1 or FAP at mRNA level when PCSK9 is inhibited. We can conclude that PCSK9 plays a key role in LSEC during Liver Colorectal Metastasis affecting significantly on proliferation and showing a particular nuclear location. Although the metabolic pathway remains undetermined, the proteomic and RNAseq studies have provided us with some molecules that seem to interact with PCSK9 and that could explain the particular function of PCSK9 in LSECs during the metastatic process
Citation Format: Ander Martin-San Sebastian, Helena García-García, Géraldine Siegfried, Abdel-Majid Khatib, Iker Badiola. PCSK9 expression in liver sinusoidal endothelial cells during liver metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1311.