Methods for analysis of AP-3/Rabin4' in regulation of lysosome distribution.

The position of lysosomes in the cytoplasm is important for their ability to fuse with the plasma membrane and release of proteases that are involved in tissue remodeling. Motor-directed bidirectional transport along microtubules is a critical process determining the distribution of lysosomes. How lysosomes are tethered to microtubules is incompletely understood, but a role for small GTPases of rab and arl families has been documented.

AP-3 and Rabip4' coordinately regulate spatial distribution of lysosomes.

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.

Assembly of the biogenesis of lysosome-related organelles complex-3 (BLOC-3) and its interaction with Rab9.

The Hermansky-Pudlak syndrome (HPS) is a genetic hypopigmentation and bleeding disorder caused by defective biogenesis of lysosome-related organelles (LROs) such as melanosomes and platelet dense bodies. HPS arises from mutations in any of 8 genes in humans and 16 genes in mice. Two of these genes, HPS1 and HPS4, encode components of the biogenesis of lysosome-related organelles complex-3 (BLOC-3).

Drosophila Sec16 mediates the biogenesis of tER sites upstream of Sar1 through an arginine-rich motif.

tER sites are specialized cup-shaped ER subdomains characterized by the focused budding of COPII vesicles. Sec16 has been proposed to be involved in the biogenesis of tER sites by binding to COPII coat components and clustering nascent-coated vesicles. Here, we show that Drosophila Sec16 (dSec16) acts instead as a tER scaffold upstream of the COPII machinery, including Sar1.

Rabip4' is an effector of rab5 and rab4 and regulates transport through early endosomes.

We describe the characterization of an 80-kDa protein cross-reacting with a monoclonal antibody against the human La autoantigen. The 80-kDa protein is a variant of rabip4 with an N-terminal extension of 108 amino acids and is expressed in the same cells. For this reason, we named it rabip4'.