A Novel TIP30 Protein Complex Regulates EGF Receptor Signaling and Endocytic Degradation

Hua Xiao,Chengliang Zhang,Xinchun Zhang,Aimin Li

doi:10.1074/jbc.m110.207720

Abstract

Activated epidermal growth factor receptor (EGFR) continues to signal in the early endosome, but how this signaling process is regulated is less well understood. Here we describe a protein complex consisting of TIP30, endophilin B1, and acyl-CoA synthetase long chain family member 4 (ACSL4) that interacts with Rab5a and regulates EGFR endocytosis and signaling. These proteins are required for the proper endocytic trafficking of EGF-EGFR. Knockdown of TIP30, ACSL4, endophilin B1, or Rab5a in human liver cancer cells or genetic knock-out of Tip30 in mouse primary hepatocytes results in the trapping of EGF-EGFR complexes in early endosomes, leading to delayed EGFR degradation and prolonged EGFR signaling. Furthermore, we show that Rab5a colocalizes with vacuolar (H(+))-ATPases (V-ATPases) on transport vesicles. The TIP30 complex facilitates trafficking of Rab5a and V-ATPases to EEA1-positive endosomes in response to EGF. Together, these results suggest that this TIP30 complex regulates EGFR endocytosis by facilitating the transport of V-ATPases from trans-Golgi network to early endosomes.

Highlights

Acidic luminal pH in early endosomes is the driving force for receptors to release their ligands, such as insulin and low density lipoprotein (LDL) [1, 2]
TIP30 Forms a Complex with Rab5a, Endo B1, and acyl-CoA synthetase long chain family member 4 (ACSL4)— To identify cytosolic proteins that interact with TIP30, we stably expressed TIP30 protein with an HA tag fused to its C-terminal end (TIP30-HA) in human hepatocellular carcinoma cells (PLC/PRF/5)
Endo B1 failed to be immunoprecipitated with ACSL4-HA, possibly due to the interference of HA at its C terminus, endogenous ACSL4 was detected in Endo B1-HA immunoprecipitates

Summary

Introduction

Acidic luminal pH in early endosomes is the driving force for receptors to release their ligands, such as insulin and low density lipoprotein (LDL) [1, 2]. We report that a newly identified protein complex containing TIP30, ACSL4, and Endo B1 drives EGF-EGFR complex endocytic trafficking by facilitating the localization of Rab5a and V-ATPases to early endosomes.

Results

Conclusion