Ser298 of MITF, a mutation site in Waardenburg syndrome type 2, is a phosphorylation site with functional significance.
MITF (microphthalmia-associated transcription factor) is a basic-helix-loop-helix-leucine zipper (bHLHZip) factor which regulates expression of tyrosinase and other melanocytic genes via a CATGTG promoter sequence, and is involved in melanocyte differentiation. Mutations of MITF in mice or humans with Waardenburg syndrome type 2 (WS2) often severely disrupt the bHLHZip domain, suggesting the importance of this structure. Here, we show that Ser298, which locates downstream of the bHLHZip and was previously found to be mutated in individuals with WS2, plays an important role in MITF function. Glycogen synthase kinase 3 (GSK3) was found to phosphorylate Ser298 in vitro, thereby enhancing the binding of MITF to the tyrosinase promoter. The same serine was found to be phosphorylated in vivo, and expression of dominant-negative GSK3beta selectively suppressed the ability of MITF to transactivate the tyrosinase promoter. Moreover, mutation of Ser298, as found in a WS2 family, disabled phos-phorylation of MITF by GSK3beta and impaired MITF function. These findings suggest that the Ser298 is important for MITF function and is phosphorylated probably by GSK3beta.
Takeda
K
K
Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Sendai 980-8575, Japan.
Takemoto
C
C
Kobayashi
I
I
Watanabe
A
A
Nobukuni
Y
Y
Fisher
D E
DE
Tachibana
M
M
D019943:Amino Acid Substitution; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D005799:Genes, Dominant; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D051379:Mice; D051739:Microphthalmia-Associated Transcription Factor; D014442:Monophenol Monooxygenase / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D012694:Serine / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014849:Waardenburg Syndrome / Q000235:genetics*
D004268:DNA-Binding Proteins; C497234:MITF protein, human; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D011994:Recombinant Proteins; D014157:Transcription Factors; D012694:Serine; D014442:Monophenol Monooxygenase; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3