Expression of genes for microphthalmia isoforms, Pax3 and MSG1, in human melanomas.
Microphthalmia (MITF) gene product, a transcription factor of the basic-helix-loop-helix type, is thought to play a role in the regulation of genes encoding the enzymes necessary for melanogenesis. These include tyrosinase, TRP-1 and TRP-2. Melanocyte-specific isoform of microphthalmia, MITF-M, is expressed in normal and malignant melanocytes. The presence of two other isoforms of microphthalmia, MITF-A and MITF-H, which differ from MITF-M in the amino-terminus, was demonstrated also in some non-melanocytic lineages. Here we have analyzed the presence of all three known isoforms of MITF mRNA in a panel of 17 human melanoma cell lines by a reverse transcriptase-polymerase chain reaction using isoform-specific primers. While, as expected, the predominant form in melanoma cell lines was MITF-M, low amounts of MITF-A mRNA was found in almost all melanomas, as well as in most of 20 tumor cell lines of the non-melanocyte origin (lung and colon carcinomas, osteosarcomas and neuroblastomas). The expression of MITF-H was not detected, with a few exceptions, in the tested cell lines. Pax3 transcription factor was reported earlier to regulate positively the melanocyte-specific promoter of the MITF gene. We found here that the Pax 3 mRNA was expressed in all melanoma cell lines, even in those that had repressed the MITF-M and were amelanotic. This suggests that additional factors, besides Pax3, are required for the MITF expression. The MSG1 (melanocyte-specific gene 1), a gene originally isolated from melanocytes and containing a strong transcription activation domain, was also found expressed in all melanomas and most non-melanocyte tumor cell lines. Together, these data indicate that the MITF-M isoform is the major type of MITF mRNA present in human melanoma cell lines and show that the expression of the isoform MITF-A and the MSG1 is not restricted to malignant melanocytes and occurs in a wide range of tumor cell lines.
Vachtenheim
J
J
Laboratory of Molecular Biology, University Hospital, 3rd Medical Faculty, Charles University, Prague 8-Bulovka, Czech Republic. jivach@upn.anet.cz
Novotná
H
H
D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008543:Melanins / Q000096:biosynthesis; D008544:Melanocytes / Q000378:metabolism*; D008545:Melanoma / Q000235:genetics* / Q000378:metabolism; D051739:Microphthalmia-Associated Transcription Factor; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D009369:Neoplasms / Q000378:metabolism / Q000473:pathology; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D000072041:PAX3 Transcription Factor; D051761:Paired Box Transcription Factors; D020033:Protein Isoforms / Q000096:biosynthesis / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012471:Salivary Proteins and Peptides / Q000096:biosynthesis / Q000235:genetics*; D014157:Transcription Factors; D014407:Tumor Cells, Cultured / Q000378:metabolism
D004268:DNA-Binding Proteins; C497234:MITF protein, human; D008543:Melanins; D051739:Microphthalmia-Associated Transcription Factor; D009363:Neoplasm Proteins; D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051761:Paired Box Transcription Factors; D020033:Protein Isoforms; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D012471:Salivary Proteins and Peptides; C087429:Smr3a protein, mouse; D014157:Transcription Factors; C068686:Pax3 protein, mouse