LAPTM4B is a PtdIns(4,5)P2 effector that regulates EGFR signaling, lysosomal sorting, and degradation

Area of Science:

• Cell Biology
• Molecular Biology
• Oncology

Background:

• Lysosomal degradation terminates epidermal growth factor receptor (EGFR) signaling.
• EGFR sorting into intraluminal vesicles (ILVs) of multivesicular endosomes (MVEs) is crucial for this degradation.
• While ESCRT machinery is known to regulate EGFR sorting, the role of endosomal transmembrane proteins remains unclear.

Purpose of the Study:

• To investigate the role of the endosomal transmembrane oncoprotein LAPTM4B in EGFR sorting and signaling.
• To elucidate the molecular mechanism by which LAPTM4B affects EGFR trafficking.
• To identify regulators that counteract LAPTM4B's inhibitory function.

Main Methods:

• Investigated the effect of LAPTM4B on EGFR sorting and degradation using cellular assays.
• Examined the interaction between LAPTM4B, Hrs, and EGFR.
• Analyzed the role of PIPKIγi5, PtdIns(4,5)P2, and SNX5 in modulating LAPTM4B's function.

Main Results:

• LAPTM4B inhibits EGF-induced EGFR intraluminal sorting and lysosomal degradation, prolonging EGFR signaling.
• LAPTM4B promotes Hrs ubiquitination, disrupting Hrs-EGFR association.
• PIPKIγi5 binding to LAPTM4B generates PtdIns(4,5)P2, recruiting SNX5 to protect Hrs from ubiquitination and promote EGFR sorting.

Conclusions:

• LAPTM4B acts as an inhibitor of EGFR intraluminal sorting and degradation.
• A novel regulatory pathway involving LAPTM4B, PtdIns(4,5)P2 signaling, and the ESCRT complex controls EGFR trafficking.
• LAPTM4B's oncogenic function in cell transformation and tumor progression is mediated by its disruption of EGFR lysosomal degradation.