Functional Analysis of Microphthalmia-associated Transcription Factor in Pigment Cell-specific Transcription of the Human Tyrosinase Family Genes

Abstract

Tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2 are the enzymes involved in melanin biosynthesis and are preferentially expressed in pigment cells. Their human gene promoters share the 11-base pair M box containing a CATGTG motif, which was shown here to be bound in vitro by microphthalmia-associated transcription factor (MITF). Transient cotransfection analysis showed that MITF overexpression increased the expression of a reporter gene under the control of the human tyrosinase or TRP-1 gene promoter but not the TRP-2 promoter. The promoter activation caused by MITF is dependent on each CATGTG motif of the distal enhancer element, the M box, and the initiator E box of the tyrosinase gene and the TRP-1 M box. Furthermore, a truncated MITF lacking the carboxyl-terminal 125 amino acid residues transactivated the tyrosinase promoter less efficiently than did MITF, suggesting that MITF's carboxyl terminus contains a transcriptional activation domain, but unexpectedly such a truncated MITF remarkably transactivated the TRP-2 gene promoter. These results suggest that MITF is sufficient to direct pigment cell-specific transcription of the tyrosinase and TRP-1 genes but not the TRP-2 gene.

The melanocyte inducing factor MITF is stably expressed in cell lines from human clear cell sarcoma

“…Microphthalmia-associated transcription factor-M functions in melanocyte differentiation and survival, and directly activates the promoters of genes, including tyrosinase, that are required for pigment production (Bentley et al, 1994;Hemesath et al, 1994;Yavuzer et al, 1995;Yasumoto et al, 1997). To evaluate the downstream effects of Mitf-M expression in CCS cells, we surveyed expression of tyrosinase ( Figure 3B, bottom panel) by Western blotting (using tyrosinase antibody C19, Santa Cruz, CA.).…”

“…The Mitf-M isoform is melanocyte specific and can induce melanocytic differentiation (Tachibana et al, 1996), indicating that Mitf-M is a critical melanogenic factor. Microphthalmia-associated transcription factor acts in part via direct transcriptional activation of genes (tyrosinase, TYRP1 and TYRP2) required for pigment synthesis (Bentley et al, 1994;Hemesath et al, 1994;Yavuzer et al, 1995;Yasumoto et al, 1997) and also has a role in melanocyte survival and differentiation (Lerner et al, 1986;Opdecamp et al, 1997;Hemesath et al, 1998). *Correspondence: Dr CR Goding; E-mail: c.goding@mcri.ac.uk With respect to CCS, it is significant that transcription of the Mitf-M isoform is controlled by a melanocyte-specific promoter (Fuse et al, 1996) that includes a cAMP-response element (CRE) comprising a single ATF1/CREB binding site (Bertolotto et al, 1998).…”

Involvement of Nurr-1/Nur77 in corticotropin-releasing factor/urocortin1-induced tyrosinase-related protein 1 gene transcription in human melanoma HMV-II cells

“…Three enzymes are involved in melanogenesis: tyrosinase, tyrosinase-related protein 1 (TRP1), and DOPA chrome tautomerase (Dct)/tyrosinase related protein (TRP2) (Körner and Pawelek, 1982;Kobayashi et al, 1994;Yokoyama et al, 1994), with MITF as a key regulator of expression. MITF binds to their binding elements, M box and E box, on the gene promoters of these enzymes, leading to stimulation of melanin synthesis (Yasumoto et al, 1997). MITF-induced TRP1 is mainly involved in the modulation of pigment production in response to stressors.…”

Altered expression of the iron transporter Nramp1 (Slc11a1) during fetal development of the retinal pigment epithelium in microphthalmia-associated transcription factor Mitfmi and Mitfvitiligo mouse mutants

“…The Mitf mi/mi mutation corresponds to a 3 base-pair deletion that results in a loss of DNA binding and Mitf transcriptional activity (Hodgkinson et al, 1993). Mitf is known to regulate several genes involved in pigment formation, including tyrosinase, tyrosinase-related protein, and dopachrome tautomerase, among others (Yasumoto et al, 1997). Loss of Mitf transcriptional activity in Mitf mi/mi mutant mice therefore results in pigmentation defects, allowing the different genotypes to be distinguished phenotypically by coat color.…”

“…As the melanosome matures, pigment granules are deposited and polymerized along the fibrillar matrix scaffold (Dell'Angelica, 2003). Mitf appears to be involved in gene regulation at all stages of melanosome biogenesis, fibrillar matrix formation, and pigment synthesis/deposition (Yasumoto et al, 1997).…”