Regulation of cargo transfer between ESCRT-0 and ESCRT-I complexes by flotillin-1 during endosomal sorting of ubiquitinated cargo

S Bänfer,J Koskimies,R Jacob,R Tikkanen,M Amaddii,U Gärtner,M Meister

doi:10.1038/oncsis.2017.47

Abstract

Ubiquitin-dependent sorting of membrane proteins in endosomes directs them to lysosomal degradation. In the case of receptors such as the epidermal growth factor receptor (EGFR), lysosomal degradation is important for the regulation of downstream signalling. Ubiquitinated proteins are recognised in endosomes by the endosomal sorting complexes required for transport (ESCRT) complexes, which sequentially interact with the ubiquitinated cargo. Although the role of each ESCRT complex in sorting is well established, it is not clear how the cargo is passed on from one ESCRT to the next. We here show that flotillin-1 is required for EGFR degradation, and that it interacts with the subunits of ESCRT-0 and -I complexes (hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and Tsg101). Flotillin-1 is required for cargo recognition and sorting by ESCRT-0/Hrs and for its interaction with Tsg101. In addition, flotillin-1 is also required for the sorting of human immunodeficiency virus 1 Gag polyprotein, which mimics ESCRT-0 complex during viral assembly. We propose that flotillin-1 functions in cargo transfer between ESCRT-0 and -I complexes.

Highlights

Signalling by receptors such as the epidermal growth factor receptor (EGFR) is downregulated by degradation of the receptor in lysosomes, which requires the receptor to be ubiquitin modified
Ubiquitinated cargo destined for lysosomal degradation is recognised and sorted by the endosomal sorting complexes required for transport (ESCRTs; reviewed in Henne et al.1)
The initial recognition of ubiquitinated cargo and recruitment of ESCRT-I is conducted by the ESCRT-0 complex, which contains two subunits, hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and signal-transducing adaptor molecule 1/2 (STAM 1/2)

Summary

INTRODUCTION

Signalling by receptors such as the epidermal growth factor receptor (EGFR) is downregulated by degradation of the receptor in lysosomes, which requires the receptor to be ubiquitin modified. Ubiquitinated cargo destined for lysosomal degradation is recognised and sorted by the endosomal sorting complexes required for transport (ESCRTs; reviewed in Henne et al.[1]). ESCRTs sequentially bind to the ubiquitinated cargo in endosomes and sequester it into intralumenal vesicles, thereby generating multivesicular bodies that deliver the cargo to lysosomes.[2,3] The initial recognition of ubiquitinated cargo and recruitment of ESCRT-I is conducted by the ESCRT-0 complex, which contains two subunits, hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and signal-transducing adaptor molecule 1/2 (STAM 1/2). We here show that flotillin-1, which we have previously demonstrated to regulate EGFR signalling but not EGFR uptake from the plasma membrane,[19] is involved in the recognition and sorting of ubiquitinated cargo by ESCRT-0 and -I

RESULTS

DISCUSSION

MATERIALS AND METHODS