MFSD12, the major facilitator superfamily domain containing 12 protein, is essential as a transmembrane transporter. It mediates the import of cysteine into melanosomes and lysosomes [1]. This function is crucial for maintaining normal levels of cystine in melanosomes, producing precursors for pheomelanin synthesis, and for redox regulation in cells as cyst(e)ine is a key precursor for glutathione synthesis [1,2]. It is also involved in lysosomal lipid peroxidation regulation and glycosphingolipid metabolism by modulating lysosome homeostasis [3,4]. Genetic models like mouse models are valuable for studying MFSD12.

In a mouse knock-in model mimicking the human MFSD12 p.Tyr182His variant, the mice showed an altered coat color, indicating the role of this variant in mammalian pigmentation [6]. In cystinosis experimental models, MFSD12 knockout led to reduced cystine levels in patient-derived proximal tubular epithelial cells and zebrafish embryos, though without improvement in proximal tubular function [5]. In breast cancer cells, MFSD12-T254A mutant inhibited MFSD12 function and suppressed tumor progression [2].

In conclusion, MFSD12 plays vital roles in cysteine transport into melanosomes and lysosomes, which impacts pigmentation, redox regulation, and lysosomal function. Studies using KO/CKO mouse models and other genetic models have revealed its significance in conditions like cystinosis and cancer, providing insights into potential therapeutic targets for these diseases.