The BLOS1‐Interacting Protein KXD1 is Involved in the Biogenesis of Lysosome‐Related Organelles

Abstract

Biogenesis of lysosome-related organelles complex-1 (BLOC-1) is an eight-subunit complex involved in lysosomal trafficking. Interacting proteins of these subunits expand the understanding of its biological functions. With the implementation of the naïve Bayesian analysis, we found that a human uncharacterized 20 kDa coiled-coil KxDL protein, KXD1, is a BLOS1-interacting protein. In vitro binding assays confirmed the interaction between BLOS1 and KXD1. Mouse KXD1 homolog was widely expressed and absent in Kxd1 knockout (KO) mice. BLOS1 was apparently reduced in Kxd1-KO mice. Mild defects in the melanosomes of the retinal pigment epithelia and in the platelet dense granules of the Kxd1-KO mouse were observed, mimicking a mouse model of mild Hermansky-Pudlak syndrome that affects the biogenesis of lysosome-related organelles.

Biogenesis of Lysosome-related Organelles Complex-1 Subunit 1 (BLOS1) Interacts with Sorting Nexin 2 and the Endosomal Sorting Complex Required for Transport-I (ESCRT-I) Component TSG101 to Mediate the Sorting of Epidermal Growth Factor Receptor into Endosomal Compartments

“…Immunoblotting-Cultured cells or tissue lysates were prepared in lysis buffer containing 50 mM Tris-HCl, pH 7.4, 150 mM NaCl, 1% Triton X-100 with protease inhibitor mixture (Sigma) at 4°C for 1 h. The immunoblotting procedures were described previously (3).…”

“…The constructs used in this study are listed in the figures, and the procedures were described previously (3).…”

“…Recent studies have shown that KXD1 is an additional putative BLOC-1 subunit in mammals or yeast (3,4). Two subcomplexes (pallidin-cappuccino-BLOS1 and dysbindin-snapin-BLOS2) exist in this BLOC-1 macro-complex (5).…”

Impaired maturation of large dense-core vesicles in muted-deficient adrenal chromaffin cells

“…KXD1 has been identified as an additional subunit of BLOC-1 (Hayes et al, 2011;John Peter et al, 2013;Yang et al, 2012). Current understanding of the functions of BLOC-1 are mainly focused on cargo trafficking from endosomes to lysosomes (for a review, see Wei and Li, 2013) and endosomal maturation (John Peter et al, 2013).…”

“…BLOC-1 deficiency causes Hermansky-Pudlak syndrome (HPS) in mice and humans, which is characterized by LRO dysfunction (Wei and Li, 2013). The KXD1-knockout mice (Yang et al, 2012) exhibit mild defects in LROs compared with other typical HPS mouse mutants of BLOC-1 such as the sdy (dysbindin deficiency), mu (muted deficiency) and pa (pallidin deficiency) mice, whereas snapin-and BLOS1-knockout mice are embryonic lethal and exhibit impaired autophagy (Cai et al, 2010;Scott et al, 2014;Tian et al, 2005;Zhang et al, 2014). This suggests that the deficiency of different BLOC-1 subunit leads to variable phenotypes on LROs.…”