# TTC36-Mediated Tumor Suppression via YBX3/SPRED1 Axis Paradoxically Reduces Sorafenib Sensitivity in Hepatocellular Carcinoma

## TL;DR

This study finds that TTC36 suppresses liver cancer growth but causes resistance to the drug sorafenib, suggesting personalized treatment strategies based on TTC36 levels.

## Contribution

The study reveals a novel tumor suppressor mechanism involving TTC36, YBX3, and SPRED1, and identifies a paradoxical resistance pathway to sorafenib in HCC.

## Key findings

- TTC36 downregulation promotes HCC proliferation and correlates with poor survival.
- TTC36 stabilizes YBX3, which enhances SPRED1 mRNA stability and suppresses Ras/MAPK signaling.
- TTC36-high HCC develops sorafenib resistance via PI3K/Akt activation, which can be reversed by Akt inhibition.

## Abstract

Background: Hepatocellular carcinoma (HCC) exhibits limited therapeutic responses, partly due to undefined tumor suppressor networks. While TTC36 is downregulated in HCC and correlates with poor prognosis, its functional role, molecular mechanisms, and impact on targeted therapy remain unknown.

Methods: By analyzing HCC tissues RNA-seq, and scRNA-seq data of HCC tissues, we investigated the expression pattern of TTC36. The clinical relevance was analyzed by using Kaplan-Meier Plotter. Cell proliferation, migration, invasion and apoptosis were detected to confirm the function of TTC36. Mechanistic insights into TTC36-mediated HCC suppression were obtained via RNA-seq analysis, mass spectrometry analysis, molecular docking, RNA pulldown, dual-luciferase reporter assays. In animal models, the tumor growth analysis, along with IHC staining and TUNNEL staining, was used to investigate the function of TTC36 and the response to sorafenib.

Results: Bioinformatics and in vitro/vivo assays demonstrated TTC36 downregulation promotes HCC proliferation and correlates with poor survival. Mechanistically, TTC36 directly binds YBX3 and masks ubiquitination sites (K311/K350), inhibiting proteasomal degradation. Stabilized YBX3 enhances SPRED1 mRNA stability by binding the CACAUC motif in its 3'UTR, suppressing Ras/MAPK signaling. The TTC36/YBX3/SPRED1 axis inhibits tumor growth but induces sorafenib resistance via compensatory PI3K/Akt activation. Akt inhibition (MK-2206) reverses sorafenib resistance in TTC36-high HCC.

Conclusion: TTC36 is a tumor suppressor that stabilizes YBX3 to upregulate SPRED1 and inhibit Ras/MAPK-driven proliferation. Paradoxically, TTC36-high HCC develops sorafenib resistance through PI3K/Akt hyperactivation, which is overcome by combined Akt inhibition. Thus, TTC36 may serves as a predictive biomarker to stratify HCC patients for personalized therapy: sorafenib monotherapy for TTC36-low tumors and sorafenib-Akt inhibitor combination for TTC36-high, sorafenib-resistant tumors.