ABSTRACT
Protection of skin against UV light requires a coordinated interaction between melanocytes and keratinocytes. Melanosomes are lysosome-related organelles that originate in melanocytes and are transferred into keratinocytes where they form a supranuclear cap. The mechanism responsible for melanosome transfer into keratinocytes and their intracellular distribution is poorly understood. Recently, we reported for the first time that loss-of-function mutations in the keratin K5 gene affect melanosome distribution in keratinocytes and results in a reticulate hyperpigmentation disorder, called Dowling-Degos disease. Here, we characterise the distribution and behaviour of individual K5 and K14 domains following transient and stable transfection into cells. We report that the K5 head domain is considerably more stable than the K14 head. Moreover, the distribution of the K5 head domain is altered following depolymerisation of microtubules. Following co-immunoprecipitation, we verified a specific interaction between the head domain of K5 with Hsc70, a chaperone also involved in vesicle uncoating. We hypothesise that this interaction is involved in melanosome formation or transport in keratinocytes. Alternatively, it may have a general function in the regulation of keratin assembly.
Subject(s)
HSC70 Heat-Shock Proteins/metabolism , Transport Vesicles/metabolism , Actins/metabolism , Bacterial Proteins/metabolism , Biological Transport/drug effects , Cell Line, Tumor , Desmosomes/drug effects , Desmosomes/metabolism , Fluorescent Antibody Technique , Haploidy , Humans , Keratin-14/chemistry , Keratin-14/metabolism , Keratin-5/chemistry , Keratin-5/metabolism , Luminescent Proteins/metabolism , Melanosomes/drug effects , Melanosomes/metabolism , Microtubules/drug effects , Microtubules/metabolism , Nocodazole/pharmacology , Nuclear Envelope/drug effects , Nuclear Envelope/metabolism , Nuclear Proteins/metabolism , Protein Binding/drug effects , Protein Structure, Tertiary , Skin/drug effects , Skin/pathology , Transport Vesicles/drug effectsABSTRACT
The CHIP ubiquitin ligase turns molecular chaperones into protein degradation factors. CHIP associates with the chaperones Hsc70 and Hsp90 during the regulation of signaling pathways and during protein quality control, and directs chaperone-bound clients to the proteasome for degradation. Obviously, this destructive activity should be carefully controlled. Here, we identify the cochaperone HspBP1 as an inhibitor of CHIP. HspBP1 attenuates the ubiquitin ligase activity of CHIP when complexed with Hsc70. As a consequence, HspBP1 interferes with the CHIP-induced degradation of immature forms of the cystic fibrosis transmembrane conductance regulator (CFTR) and stimulates CFTR maturation. Our data reveal a novel regulatory mechanism that determines folding and degradation activities of molecular chaperones.
