On the lysosomal degradation of neurofibromin and its phosphorylation in cultured melanocytes.
Neurofibromatosis type 1 (NF1) is one of the most common inherited disorders in humans. Most of the NF1 gene mutations result in a reduction of the amount of neurofibromin to about 50%. Recently, we found that the level of neurofibromin can be regulated post-translationally through the alteration of its half-life. Here, we investigated whether lysosomes are involved in this post-translational regulation in cultured melanocytes of NF1 patients and controls. When the lysosomal degradation was inhibited by chloroquine, an increase of neurofibromin by a factor of 2 to 3, correlating with an increased half-life, was measured. Incubation with phosphoprotein-phosphatase inhibitors also increased the neurofibromin content in melanocytes. Investigations on phosphorylation of neurofibromin revealed a basal phosphorylation in melanocytes cultured with growth factor-deprived medium that increased upon incubation with the growth stimulators PMA or bFGF. Because both factors are also able to increase the half-life of neurofibromin, we suggest its phosphorylation to be an important step in protecting neurofibromin against specific lysosomal degradation.
Kaufmann
D
D
Abteilung Humangenetik, Universität Ulm, Germany.
Junge
I
I
Bartelt
B
B
Lattke
H
H
Müller
R
R
D000818:Animals; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006207:Half-Life; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D008544:Melanocytes / Q000187:drug effects / Q000378:metabolism*; D008969:Molecular Sequence Data; D025542:Neurofibromin 1; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D025542:Neurofibromin 1; D011506:Proteins; D019319:Okadaic Acid; D002738:Chloroquine; D013755:Tetradecanoylphorbol Acetate