KBTBD8/RRP15 as a potential novel therapeutic target associates with lenvatinib-inhibited progression in hepatocellular carcinoma both in vitro and in vivo

Introduction

We have previously demonstrated that RRP15 (Ribosomal RNA Processing 15 Homolog) was significantly elevated in hepatocellular carcinoma (HCC) and correlated directly with poor prognosis. RRP15 suppression curtails HCC progression through induction of cellular senescence and apoptosis. However, the impact of RRP15 on the precise therapeutic potential of lenvatinib has remained underexplored.

Objective

To investigate the relationship between RRP15 expression and sensitivity of lenvatinib in HCC treatment, and also explore the potential of targeting RRP15 by lenvatinib to inhibit HCC progression.

Methods

RRP15 and KBTBD8 (Kelch Repeat and BTB Domain Containing 8) expression was examined using western blot and immunohistochemistry. Cell viability, proliferation, migration and invasion as well as apoptosis were assessed using CCK-8, clonogenic assays, transwell, TUNEL (Terminal Deoxynucleotidyl Transferase mediated dUTP Nick-End Labeling) and Annexin V staining assays. The interaction between RRP15 and KBTBD8 was identified through pull-down and mass spectrometry analysis and further validated by immunofluorescence and co-immunoprecipitation assays. RRP15 ubiquitination and degradation were assessed using cycloheximide treatment, plasmid transfection and co-immunoprecipitation, followed by western blot analysis. Tail vein injection lung metastasis model was performed to determine tumor metastasis in vivo.

Results

We reveled a correlation between RRP15 downregulation and enhanced sensitivity to lenvatinib, presenting marked suppression of metastasis and invasiveness. Proteomic analyses and subsequent validation disclosed the pivotal role of the E3 ubiquitin ligase KBTBD8 in mediating the ubiquitination and subsequent degradation of RRP15 protein post-lenvatinib treatment in HCC cells. KBTBD8 inhibition stalled RRP15 ubiquitination and degradation, while its overexpression accelerated these processes. Moreover, RRP15 overexpression fosters HCC cell proliferation and metastasis, a pathological effect mitigated by KBTBD8 overexpression. In vivo experiments further validate the role of lenvatinib in promoting RRP15 degradation via KBTBD8 upregulation.

Conclusions

Our study elucidated a previously unidentified mechanism of lenvatinib action and identified the RRP15-KBTBD8 axis as a novel therapeutic target in HCC, offering new avenues for treatment strategies in combating HCC.