MZF1 promotes tumour progression and resistance to anti-PD- L1 antibody treatment in hepatocellular carcinoma

Background & Aims: The mechanism underlying resistance to immunotherapy involves engagement of immune checkpoint pathways. The transcriptional and epigenetic processes of checkpoint molecules, however, have not been well investigated. We thus studied whether the transcription factor myeloid zinc finger 1 (MZF1) may promote resistance to immunotherapy in hepatocellular carcinoma (HCC). Methods: Single-cell RNA-sequencing was performed to study the correlation between MZF1 and tumour microenvironment features in six patients with HCC. Combined immunohistochemistry and multi-immunofluorescence analyses were per-formed for verification. Ectopic expression of MZF1 was used in both orthotopic and genetically engineered hydrodynamic mouse HCC models for in vivo experiments. Proteome analysis, including protein degradation assays, ubiquitination assays, and co-immunoprecipitation assays, revealed the function of MZF1 in immune checkpoint pathways. Results: Single-cell RNA-sequencing suggested an immunosuppressive environment and a strong correlation with the im-mune checkpoint programmed death ligand 1 (PD-L1) in MZF1-overexpressing tumours. Analyses of 163 HCC samples demonstrated that MZF1 expression in HCC cells is associated with decreased T-cell infiltration. In vivo experiments showed that ectopic MZF1 expression in HCC cells impairs T-cell recruitment, resulting in resistance to immune checkpoint blockade. Mechanistically, MZF1 accelerated PD-L1 ubiquitination by binding to the cyclin-dependent kinase 4 (CDK4) activation site, while a direct bond between CDK4 and MZF1 led to increased MZF1 expression. Conclusions: MZF1 promotes PD-L1 ubiquitination via CDK4 and possibly MZF1. Inhibition of CDK4 can therefore restore PD -L1 expression and may be a potential strategy for combination with anti-PD-L1 antibodies. Impact and implications: Resistance to immune checkpoint blockade with anti-programmed death ligand 1 (PD-L1) anti-body therapy is attributed to oncogenic alterations of tumour cells, however, effective countermeasures are yet to be established. Here, we report that the transcription factor myeloid zinc finger 1 (MZF1) can bind to the cyclin-dependent kinase 4 (CDK4) activation site and accelerate PD-L1 ubiquitination. A CDK4 inhibitor therefore enhances anti-PD-L1 anti-body efficacy by blocking MZF1 signalling. This indicates a potential benefit of combining CDK4 inhibitors and anti-PD-L1 antibodies for the treatment of advanced HCC. (c) 2023 The Authors. Published by Elsevier B.V. on behalf of European Association for the Study of the Liver (EASL). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study reveals the correlation between the transcription factor MZF1 and the immune checkpoint molecule PD-L1 in hepatocellular carcinoma (HCC). The overexpression of MZF1 is associated with an immunosuppressive environment and decreased T-cell infiltration in HCC. Mechanistically, MZF1 accelerates PD-L1 ubiquitination via the CDK4 pathway. Inhibition of CDK4 may restore PD-L1 expression and enhance the efficacy of anti-PD-L1 antibodies.