U. Yavuzer et Cr. Goding, MELANOCYTE-SPECIFIC GENE-EXPRESSION - ROLE OF REPRESSION AND IDENTIFICATION OF A MELANOCYTE-SPECIFIC FACTOR, MSF, Molecular and cellular biology, 14(5), 1994, pp. 3494-3503
For a gene to be transcribed in a tissue-specific fashion, expression
must be achieved in the appropriate cell type and also be prevented in
other tissues. As an approach to understanding the regulation of tiss
ue-specific gene expression, we have analyzed the requirements for mel
anocyte-specific expression of the tyrosinase-related protein 1 (TRP-1
) promoter. Positive regulation of TRP-1 expression is mediated by bot
h an octamer-binding motif and an 11-bp element, termed the M box, whi
ch is conserved between the TRP-1 and other melanocyte-specific promot
ers. We show here that, consistent with its ability to activate transc
ription in a non-tissue-specific fashion, the M box binds the basic-he
lix-loop-helix factor USF in vitro. With the use of a combination of s
ite-directed mutagenesis and chimeric promoter constructs, additional
elements involved in regulating TRP-1 expression were identified. Thes
e include the TATA region, which appears to contribute to the melanocy
te specificity of the TRP-1 promoter. Mutational analysis also identif
ied two repressor elements, one at the start site, the other located a
t -240, which function both in melanoma and nonmelanoma cells. In addi
tion, a melanocyte-specific factor, MSF, binds to sites which overlap
both repressor elements, with substitution mutations demonstrating tha
t binding by MSF is not required for repression. Although a functional
role for MSF has not been unequivocally determined, the location of i
ts binding sites leads us to speculate that it may act as a melanocyte
-specific antirepressor during transcription of the endogenous TRP-1 g
ene.