RABL2A–CCDC34 Axis Promotes Sorafenib Resistance in Hepatocellular Carcinoma

In this study, we examined the regulatory role of CCDC34 in the sorafenib sensitivity of hepatocellular carcinoma (HCC) and its functional partners. Wide-type Huh7 and Hep3B and induced sorafenib-resistant (SR) Huh7/SR and Hep3B/SR cells were used as in vitro cell models. Immunofluorescent staining and coimmunoprecipitation were performed to check protein–protein interaction. Cell Counting Kit-8 (CCK-8), terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL), PI/Annexin V staining, and western blot analysis were performed to assess cell response to sorafenib. The results showed that CCDC34 upregulation in HCC was associated with poor survival. Huh7/SR and Hep3B/SR cells had significantly higher CCDC34 expression than the parental cell lines. RABL2A expression was significantly upregulated in SR HCC cells and interacted with CCDC34 in its GTP-bound state in Huh7/SR and Hep3B/SR cells. RABL2A depletion sensitized Huh7/SR and Hep3B/SR cells to sorafenib. RABL2A Q80L mutant (GTP-bound state locked), but not S35N mutant (GDP-bound state locked) overexpression increased sorafenib IC50 of Huh7 and Hep3B cells. CCDC34 depletion nearly abrogated the protective effects of RABL2A Q80L overexpression both in vitro and in vivo. RABL2A Q80L overexpression significantly increased the expression of p-p38 and p-JNK, the effects of which were significantly attenuated by CCDC34 depletion. In summary, we infer that the RABL2A–CCDC34 axis plays an important role in mediating p38/MAPK and JNK/MAPK signaling, thereby contributing to acquired sorafenib resistance in HCC.