Syntaxin 12 and COMMD3 are new factors that function with VPS33B in the biogenesis of platelet α-granules
Syntaxin 12 and COMMD3 are new factors that function with VPS33B in the biogenesis of platelet α-granules
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DOI：
10.1182/blood.2021012056
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发表时间：
2022-02-10
期刊：
影响因子：
20.3
通讯作者：
Di Pietro, Santiago M.
中科院分区：
文献类型：
--
作者：
Ambrosio, Andrea L.;Febvre, Hallie P.;Di Pietro, Santiago M.
血小板α颗粒调节止血和无数其他生理过程，但其生物成因尚不清楚。已知只有3种蛋白质的突变会导致人类α颗粒缺陷和出血性疾病。两个这样的蛋白，VPS16B和VPS33B，形成一个复杂的介导转运新合成的α颗粒蛋白通过巨核细胞（MK）内体室。目前尚不清楚VPS16B/VPS33B复合体是如何实现这一功能的。在这里，我们报道VPS16B/VPS33B与Syntaxin 12 （Stx12）物理结合，Syntaxin 12是一种介导内体囊泡融合的SNARE蛋白。重要的是，缺乏Stx12的mk表现出α颗粒数量和α颗粒蛋白的总体水平降低，从而揭示了Stx12是a颗粒生物发生机制的新组成部分。VPS16B/VPS33B还结合CCDC22， CCDC22是CCC复合物的一个组分，在核内体出口位点起作用。CCDC22与Stx12竞争与VPS16B/VPS33B的结合，提示可能的切换机制。此外，mk中表达的主要CCC形式含有COMMD3，这是10种COMMD蛋白之一。缺乏COMMD3/CCDC22可导致α -颗粒数量和α -颗粒蛋白总体水平的降低，从而使COMMD3/CCC复合物成为α -颗粒生物发生的新因子。此外，p -选择素以COMMD3依赖的方式通过细胞表面运输，COMMD3的消耗导致p -选择素和PF4的溶酶体降解。与VPS16B/VPS33B缺陷相比，Stx12和COMMD3/CCC缺陷导致的表型较轻，这表明Stx12和COMMD3/CCC在α颗粒生物发生中起辅助作用，但不如VPS16B/VPS33B重要。在机制上，我们的研究结果表明VPS16B/VPS33B通过将融合机制与普遍存在的内体回收复合体连接起来，协调α颗粒蛋白的内体进入和退出，该复合体在mk中被重新利用以制造α颗粒。
Platelet alpha-granules regulate hemostasis and myriad other physiological processes, but their biogenesis is unclear. Mutations in only 3 proteins are known to cause alpha-granule defects and bleeding disorders in humans. Two such proteins, VPS16B and VPS33B, form a complex mediating transport of newly synthesized alpha-granule proteins through megakaryocyte (MK) endosomal compartments. It is unclear how the VPS16B/VPS33B complex accomplishes this function. Here we report VPS16B/VPS33B associates physically with Syntaxin 12 (Stx12), a SNARE protein that mediates vesicle fusion at endosomes. Importantly, Stx12-deficient MKs display reduced alpha-granule numbers and overall levels of alpha-granule proteins, thus revealing Stx12 as a new component of the a-granule biogenesis machinery. VPS16B/VPS33B also binds CCDC22, a component of the CCC complex working at endosome exit sites. CCDC22 competes with Stx12 for binding to VPS16B/VPS33B, suggesting a possible hand-off mechanism. Moreover, the major CCC form expressed in MKs contains COMMD3, one of 10 COMMD proteins. Deficiency of COMMD3/CCDC22 causes reduced alpha-granule numbers and overall levels of alpha-granule proteins, establishing the COMMD3/CCC complex as a new factor in alpha-granule biogenesis. Furthermore, P-selectin traffics through the cell surface in a COMMD3-dependent manner and depletion of COMMD3 results in lysosomal degradation of P-selectin and PF4. Stx12 and COMMD3/CCC deficiency cause less severe phenotypes than VPS16B/VPS33B deficiency, suggesting Stx12 and COMMD3/CCC assist but are less important than VPS16B/VPS33B in alpha-granule biogenesis. Mechanistically, our results suggest VPS16B/VPS33B coordinates the endosomal entry and exit of alpha-granule proteins by linking the fusogenic machinery with a ubiquitous endosomal retrieval complex that is repurposed in MKs to make alpha-granules.