Pax3 and Regulation of the Melanocyte-specific Tyrosinase-related Protein-1 Promoter

Abstract

Previous work has established that the melanocytespecific tyrosinase-related protein-1 (TRP-1) promoter is regulated positively by the microphthalmia-associated transcription factor Mitf, acting through the conserved M box and negatively by the T-box factor Tbx2, which can bind two "melanocyte-specific elements" termed the MSEu and MSEi. Both the MSEu and MSEi, which share a 6-base pair GTGTGA consensus, are also recognized by a previously unidentified melanocytespecific factor, MSF. Here we show using a combination of DNA binding assays, proteolytic clipping, and antiPax3 antibodies that MSF is indistinguishable from Pax3, a paired homeodomain transcription factor implicated genetically in melanocyte development and the regulation of the Mitf promoter. Consistent with Pax3 being able to bind the TRP-1 promoter, Pax3 is expressed in melanocytes and melanomas, and TRP-1 promoter activity is up-regulated by Pax3. The results identify a novel role for Pax3 in the expression of TRP-1, and the potential role of Pax3 in the melanocyte lineage is discussed.The development of the melanocyte lineage presents a fascinating opportunity to analyze the complex interplay between signal transduction pathways and transcription factors, which underlies development. Because melanocytes are not essential for viability and variations in pigmentation are obvious (1), over 70 independent genetic loci have been implicated in the development or function of these melanin-producing cells. Of the 20 or so that have been cloned to date, some, such as the genes encoding tyrosinase or tyrosinase-related protein-1 (TRP-1), 1 have a clearly defined function in the genesis of pigment. On the other hand, genes such as the endothelin B (2-4) and c-Kit receptors (5), and the microphthalmia (6 -8), Sox10 (9, 10), and Pax3 (11) transcription factors have been implicated in the developmental pathway leading to the genesis of the mature pigment-producing melanocyte from a nonpigmented melanoblast precursor cell originating in the trunk neural crest.Particularly interesting are mutations affecting the Pax3-paired homeodomain transcription factor, exemplified by the splotch allele (11), which expresses a truncated Pax3 protein.Although splotch homozygotes die in utero, heterozygous splotch mice exhibit pigmentation defects resulting from the loss of a proportion of the melanoblasts migrating away from the neural crest. The loss of melanocytes in splotch mice may be explained by the fact that Pax3 has recently been shown to activate expression from the promoter for the gene encoding the microphthalmia-associated basic helix-loop-helix-leucine zipper transcription factor (Mitf) (12); mice devoid of functional Mitf lack all pigment cells, and a decrease in Mitf levels resulting from monoallelic loss of Pax3 would account for the pigmentation defect exhibited by splotch mice. The ability of Pax3 to regulate expression of Mitf is paralleled by the role of Pax3 in skeletal muscle formation where it is required for expression of the basic helix-loop-helix tran...

DNA binding of USF is required for specific E-box dependent gene activation in vivo

“…Our ®ndings are consistent with the observation that USF binds to the Myc regulated E-box of the CAD gene in vivo (Boyd et al, 1998). The data do not address the molecular mechanism by which DNA binding by USF is regulated; however, several previous reports have shown that DNA binding of USF proteins is regulated by phosphorylation (Berger et al, 1998;Maekawa et al, 1991) and that the extent of phosphorylation is lower in established cell lines relative to primary cells (Galibert et al, 1997).…”

Investigation of downstream target genes of PAX3c, PAX3e and PAX3g isoforms in melanocytes by microarray analysis

“…Others such as Dhh, Msx1, Kitl, Rac1 and the markers of melanoma progression, RhoC and Timp3, were identified only in the present study. 22,23 Genes identified in other studies such as Mitf, Trp1 and Stx [13][14][15] were absent in this study. Several possible reasons exist.…”

Tyrp1 and Oculocutaneous Albinism Type 3

“…Recently, it was demonstrated that Tyrp1 gene expression could be down-regulated in melanocytic cells by activation of negative regulatory factors, even in the presence of Mitf (31). Tyrp1 expression is also regulated by 2 elements, termed MSEu and MSEi, which act as negative regulatory elements (32,33). Binding of Pax3, a paired homeodomain transcription factor involved in melanocyte development, to these elements up-regulates Tyrp1 expression (32).…”

“…Tyrp1 expression is also regulated by 2 elements, termed MSEu and MSEi, which act as negative regulatory elements (32,33). Binding of Pax3, a paired homeodomain transcription factor involved in melanocyte development, to these elements up-regulates Tyrp1 expression (32). The brachyury-related transcription factor, Tbx2, binds to the MSEu and MSEi elements of Tyrp1 and down-regulates Tyrp1 expression (33).…”