Cystine/H(+) symporter that mediates export of cystine, the oxidized dimer of cysteine, from lysosomes (PubMed:11689434, PubMed:18337546, PubMed:22232659, PubMed:29467429, PubMed:33208952, PubMed:15128704). Plays an important role in melanin synthesis by catalyzing cystine export from melanosomes, possibly by inhibiting pheomelanin synthesis (PubMed:22649030). In addition to cystine export, also acts as a positive regulator of mTORC1 signaling in kidney proximal tubular cells, via interactions with components of the v-ATPase and Ragulator complexes (By similarity). Also involved in small GTPase-regulated vesicle trafficking and lysosomal localization of LAMP2A, independently of cystine transporter activity (By similarity). H(+)(out) + L-cystine(out) = H(+)(in) + L-cystine(in) H(+)(out) + L-cystine(out) = H(+)(in) + L-cystine(in) H(+)(out) + L-cystine(out) = H(+)(in) + L-cystine(in) Interacts with components of the V-ATPase complex. Interacts with components of the Ragulator complex. Interacts with RRAGA/RagA and RRAGC/RagC (By similarity). Interacts with AP-3 complex subunit mu (AP3M1 or AP3M2) (PubMed:25753619). AP-3 complex is required for localization to the lysosome. Strongly expressed in pancreas, kidney (adult and fetal), skeletal muscle, melanocytes and keratinocytes (PubMed:22649030). Expressed at lower levels in placenta and heart. Weakly expressed in lung, liver and brain (adult and fetal) (PubMed:22649030). Represents 5-20 % of CTNS transcripts, with the exception of the testis that expresses both isoforms in equal proportions. The lysosomal targeting motif, together with the second PQ-loop mediate targeting to the lysosome. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the cystinosin family.