Meta-Biol

• Pathways

Cystinosin (CTNS) is an integral lysosomal membrane protein which can transport L-cystine (CySS-, the oxidative product of two cysteine molecules linked via a disulfide bond) together with H+ out of lysosomes. CySS- is a component of hair, skin and nails. Defects in CTNS cause cystinosis, lysosomal storage-type diseases due to defective transport of CySS- across the lysosomal membrane (Town et al. 1998, Anikster et al. 1999; review Elmonem et al. 2016). Patients with cystinosis frequently exhibit blond hair and a fair complexion, suggesting an involvement in melanogenesis. Chiaverini et al. show CTNS is also localised to melanosomes. CTNS silencing led to a 75% reduction of melanin synthesis, caused by a degradation of tyrosinase (the enzyme responsible for melanin biosynthesis), thereby identifying a role for CTNS in melanogenesis (Chiaverini et al. 2012).