Melanoma differentiation associated gene-9/syndecan binding protein promotes hepatocellular carcinoma

BACKGROUND AND AIMS

The oncogene Melanoma differentiation associated gene-9/syndecan binding protein (MDA-9/SDCBP) is overexpressed in many cancers, promoting aggressive, metastatic disease. However, the role of MDA-9 in regulating hepatocellular carcinoma (HCC) has not been well studied.

APPROACH AND RESULTS

To unravel the function of MDA-9 in HCC, we generated and characterized a transgenic mouse with hepatocyte-specific overexpression of MDA-9 (Alb/MDA-9). Compared with wild-type (WT) littermates, Alb/MDA-9 mice demonstrated significantly higher incidence of N-nitrosodiethylamine/phenobarbital-induced HCC, with marked activation and infiltration of macrophages. RNA sequencing (RNA-seq) in naive WT and Alb/MDA-9 hepatocytes identified activation of signaling pathways associated with invasion, angiogenesis, and inflammation, especially NF-κB and integrin-linked kinase signaling pathways. In nonparenchymal cells purified from naive livers, single-cell RNA-seq showed activation of Kupffer cells and macrophages in Alb/MDA-9 mice versus WT mice. A robust increase in the expression of Secreted phosphoprotein 1 (Spp1/osteopontin) was observed upon overexpression of MDA-9. Inhibition of NF-κB pathway blocked MDA-9-induced Spp1 induction, and knock down of Spp1 resulted in inhibition of MDA-9-induced macrophage migration, as well as angiogenesis.

CONCLUSIONS

Alb/MDA-9 is a mouse model with MDA-9 overexpression in any tissue type. Our findings unravel an HCC-promoting role of MDA-9 mediated by NF-κB and Spp1 and support the rationale of using MDA-9 inhibitors as a potential treatment for aggressive HCC.

Abstract 3720: Cysteine palmitoylation of astrocyte elevated gene-1/Metadherin (AEG-1/MTDH) regulates its biological and immunological activity

Non-alcoholic steatohepatitis (NASH) is a major risk factor for hepatocellular carcinoma (HCC). Astrocyte elevated gene-1/Metadherin (AEG-1/MTDH) augments steatosis, inflammation, and tumorigenesis, thereby promoting the whole spectrum of this disease process. Targeting AEG-1 is a potential interventional strategy for NASH and HCC. Thus, proper understanding of the regulation of this molecule is essential. We found that AEG-1 is palmitoylated at residue Cysteine75 (Cys75). Mutation of Cys75 to Serine (Ser) completely abolished AEG-1 palmitoylation.Systematic knockdown studies identified zinc finger DHHC-type palmitoyltransferase 6 (ZDHHC6) as the palmitoyltransferase catalyzing the process. To obtain insight into how palmitoylation regulates AEG-1 function, we generated a knock-in mouse by CRISPR/Cas9 in which Cys75 of AEG-1 was mutated to Ser (AEG-1-C75S). No developmental or anatomical abnormality was observed between AEG-1-wild type (AEG-1-WT) and AEG-1-C75S littermates. However, global gene expression analysis by RNA-sequencing unraveled that signaling pathways and upstream regulators, which contribute to cell proliferation, motility, inflammation,angiogenesis, and lipid accumulation, are activated in AEG-1-C75S hepatocytes compared toAEG-1-WT. Feeding these mice with high fat/high sugar diet for 20 weeks showed accumulation of T-regulatory cells and exhausted CD8 T-cells in the livers of AEG-1-C75S mice vs AEG-1-WT, and only in females, suggesting that inhibition of AEG-1 palmitoylation creates an immunosuppressive milieu favoring tumorigenesis. Collectively, these findings suggest that AEG-1-C75S functions as dominant positive, and palmitoylation restricts oncogenic and NASH-promoting functions of AEG-1. Studies are ongoing to unravel the mechanism by which palmitoylation restricts AEG-1 function, and to understand the sex-specific immune-modulatory role of AEG-1 palmitoylation in hepatocarcinogenesis.

Citation Format: Maria Del Carmen Camarena, Garrison Komaniecki, Debashri Manna, Rachel Mendoza, Mark A. Subler, Jolene J. Windle, Mikhail G. Dozmorov, Hening Lin, Devanand Sarkar. Cysteine palmitoylation of astrocyte elevated gene-1/Metadherin (AEG-1/MTDH) regulates its biological and immunological activity. [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 3720.

Astrocyte Elevated Gene-1 Cys75 S-Palmitoylation by ZDHHC6 Regulates Its Biological Activity

Nonalcoholic fatty liver disease is a major risk factor for hepatocellular carcinoma (HCC). Astrocyte elevated gene-1/Metadherin (AEG-1/MTDH) augments lipid accumulation (steatosis), inflammation, and tumorigenesis, thereby promoting the whole spectrum of this disease process. Targeting AEG-1 is a potential interventional strategy for nonalcoholic steatohepatitis (NASH) and HCC. Thus, proper understanding of the regulation of this molecule is essential. We found that AEG-1 is palmitoylated at residue cysteine 75 (Cys75). Mutation of Cys75 to serine (Ser) completely abolished AEG-1 palmitoylation. We identified ZDHHC6 as a palmitoyltransferase catalyzing the process in HEK293T cells. To obtain insight into how palmitoylation regulates AEG-1 function, we generated knock-in mice by CRISPR/Cas9 in which Cys75 of AEG-1 was mutated to Ser (AEG-1-C75S). No developmental or anatomical abnormality was observed between AEG-1-wild type (AEG-1-WT) and AEG-1-C75S littermates. However, global gene expression analysis by RNA-sequencing unraveled that signaling pathways and upstream regulators, which contribute to cell proliferation, motility, inflammation, angiogenesis, and lipid accumulation, were activated in AEG-1-C75S hepatocytes compared to AEG-1-WT. These findings suggest that AEG-1-C75S functions as dominant positive and that palmitoylation restricts oncogenic and NASH-promoting functions of AEG-1. We thus identify a previously unknown regulatory mechanism of AEG-1, which might help design new therapeutic strategies for NASH and HCC.