Levin-Konigsberg Roni, Mitra Koushambi, Spees Kaitlyn, Nigam AkshatKumar, Liu Katherine, Januel Camille, Hivare Pravin, Arana Sophia M, Prolo Laura M, Kundaje Anshul, Leonetti Manuel D, Krishnan Yamuna, Bassik Michael C
Department of Genetics, Stanford School of Medicine, Stanford, CA 94305, USA.
Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA; Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA; Institute of Biophysical Dynamics, The University of Chicago, Chicago, IL 60637, USA.
Dev Cell. 2025 Jan 20;60(2):220-235.e7. doi: 10.1016/j.devcel.2024.10.003. Epub 2024 Oct 29.
Ammonia is a ubiquitous, toxic by-product of cell metabolism. Its high membrane permeability and proton affinity cause ammonia to accumulate inside acidic lysosomes in its poorly membrane-permeant form: ammonium (NH). Ammonium buildup compromises lysosomal function, suggesting the existence of mechanisms that protect cells from ammonium toxicity. Here, we identified SLC12A9 as a lysosomal-resident protein that preserves organelle homeostasis by controlling ammonium and chloride levels. SLC12A9 knockout (KO) cells showed grossly enlarged lysosomes and elevated ammonium content. These phenotypes were reversed upon removal of the metabolic source of ammonium or dissipation of the lysosomal pH gradient. Lysosomal chloride increased in SLC12A9 KO cells, and chloride binding by SLC12A9 was required for ammonium transport. Our data indicate that SLC12A9 function is central for the handling of lysosomal ammonium and chloride, an unappreciated, fundamental mechanism of lysosomal physiology that may have special relevance in tissues with elevated ammonia, such as tumors.
氨是细胞代谢中普遍存在的有毒副产物。其高膜通透性和质子亲和力导致氨以膜通透性较差的形式（铵，NH）在酸性溶酶体内积累。铵的积累损害溶酶体功能，这表明存在保护细胞免受铵毒性的机制。在这里，我们鉴定出SLC12A9是一种定位于溶酶体的蛋白质，它通过控制铵和氯离子水平来维持细胞器的稳态。SLC12A9基因敲除（KO）细胞显示溶酶体明显增大且铵含量升高。去除铵的代谢来源或消除溶酶体pH梯度后，这些表型得以逆转。SLC12A9 KO细胞中溶酶体氯离子增加，铵转运需要SLC12A9与氯离子结合。我们的数据表明，SLC12A9的功能对于处理溶酶体中的铵和氯离子至关重要，这是溶酶体生理学中一种未被重视的基本机制，可能在氨水平升高的组织（如肿瘤）中具有特殊意义。
