AP-3 and Rabip4’ Coordinately Regulate Spatial Distribution of Lysosomes

Abstract

The RUN and FYVE domain proteins rabip4 and rabip4’ are encoded by RUFY1 and differ in a 108 amino acid N-terminal extension in rabip4’. Their identical C terminus binds rab5 and rab4, but the function of rabip4s is incompletely understood. We here found that silencing RUFY1 gene products promoted outgrowth of plasma membrane protrusions, and polarized distribution and clustering of lysosomes at their tips. An interactor screen for proteins that function together with rabip4’ yielded the adaptor protein complex AP-3, of which the hinge region in the β3 subunit bound directly to the FYVE domain of rabip4’. Rabip4’ colocalized with AP-3 on a tubular subdomain of early endosomes and the extent of colocalization was increased by a dominant negative rab4 mutant. Knock-down of AP-3 had an ever more dramatic effect and caused accumulation of lysosomes in protrusions at the plasma membrane. The most peripheral lysosomes were localized beyond microtubules, within the cortical actin network. Our results uncover a novel function for AP-3 and rabip4’ in regulating lysosome positioning through an interorganellar pathway.

Matrix Proteins of Nipah and Hendra Viruses Interact with Beta Subunits of AP-3 Complexes

“…Interestingly, this AP3B1 Hinge region has been studied previously in the context of two different cellular binding partners: kinesin family member 3A (Kif3A) (45) and rabip4= (56). The interaction between AP3B1 and Kif3A was identified in a yeast two-hybrid screen, using a Hinge-containing fragment of AP3B1 as bait (45).…”

“…In addition, the interaction was found to be important for HIV-1 particle release, as release of HIV-1 Gag VLPs could be inhibited either through siRNA depletion of Kif3A or by expression of a motorless Kif3A polypeptide that binds AP3B1 and presumably acts as a competitive inhibitor to block AP3B1 interaction with full-length, endogenous Kif3A (45). In a separate study, binding partners for the endosomal protein rabip4= were isolated using an affinity pulldown procedure followed by mass spectrometry, and this identified an interaction between rabip4= and AP3B1 (56). Mapping studies showed that the Hinge domain of AP3B1 bound to the FYVE domain of rabip4=, and knockdown studies suggested that AP-3:rabip4= complexes are likely important for proper control of lysosome distribution within cells (56).…”

“…In a separate study, binding partners for the endosomal protein rabip4= were isolated using an affinity pulldown procedure followed by mass spectrometry, and this identified an interaction between rabip4= and AP3B1 (56). Mapping studies showed that the Hinge domain of AP3B1 bound to the FYVE domain of rabip4=, and knockdown studies suggested that AP-3:rabip4= complexes are likely important for proper control of lysosome distribution within cells (56). Taken together with our results obtained with the henipavirus M proteins, these studies suggest that the AP3B1 Hinge domain is capable of directing protein interactions with a variety of partners.…”

Podocalyxin‐like protein promotes gastric cancer progression through interacting with RUN and FYVE domain containing 1 protein

“…RUN and FYVE domain containing 1 (RUFY1) is a member of the RUFY family, whose members contain an N‐terminal RUN domain and a C‐terminal FYVE domain . RUFY proteins are localized predominantly to early endosomes and participate in the regulation of diverse cellular processes . For example, RUFY1 acted as a downstream effector of Etk.…”

“…25,26 RUFY proteins are localized predominantly to early endosomes and participate in the regulation of diverse cellular processes. 25,[27][28][29][30] For example, RUFY1 acted as a downstream effector of Etk. Tyrosine phosphorylation of RUFY1 by Etk might be important for its endosomal localization.…”