Interventional gene targeting of the cell cycle regulator Cyclin E1 during hepatocarcinogenesis attenuates cancer progression with limited proliferation, stemness traits and micro-metastasis

Background and aims Hepatocellular carcinoma (HCC) develops as a multi-stage process based on chronic hepatitis that leads to chromosomal aberrations and oncogenic events. E-type cyclins (CcnE1, CcnE2) and Cyclin-dependent kinase 2 (Cdk2) are key mediators during cell cycle progression. Recently, we demonstrated an essential role of CcnE1 and Cdk2, but not CcnE2, for the initiation of HCC in a prevention model. In the present study, we investigated the therapeutic benefit of targeting CcnE1 or Cdk2 after the onset of hepatocarcinogenesis.

Method Two-week-old conditional CcnE1 or Cdk2 mice with inducible Cre-recombinase under control of the Mx-gene promoter were injected with diethylnitrosamine. Cre-negative littermates served as controls. After 22 weeks (early HCC progression), interventional inactivation of CcnE1 or Cdk2 in liver cells and hematopoietic cell was induced by poly-I:poly-C injections. Sixteen weeks after treatment, tumor number and size were analyzed. Liver and tumor tissues were mechanistically and pathologically investigated for markers of proliferation, stemness, DNA repair and metastasis. The hepatic microenvironment was analyzed via flow cytometry and immunohistochemistry. Human HCC in silico analysis was based on GTex and TCGA.

Results Interventional inactivation of CcnE1 during HCC progression resulted in a reduction of tumor number and size compared to controls and was associated with decreased proliferation, stem cell traits and an absence of micro-metastasis. Importantly, the absence of CcnE1 was associated with reduced DNA repair, which illustrates the relevance of aberrant CcnE1 expression for the promotion of mutations by negatively affecting DNA integrity. Moreover, CcnE1 inactivation limited the presence of myeloid subpopulations, pointing to a potential role of CcnE1 in immune cell function or homing. In contrast, interventional inactivation of Cdk2 did not reveal any beneficial effects. Finally, CcnE1 levels were found to be associated with aneuploidy, stemness and disease recurrence in human HCCs.

Conclusion Cdk2 is fully dispensable for HCC progression. Interventional inactivation of CcnE1 during HCC progression attenuates disease development and presents a promising target for the treatment of HCC patients.

Publication History

Article published online:
08 September 2020