Mmip1: a novel leucine zipper protein that reverses the suppressive effects of Mad family members on c-myc.
C-myc, a member of the basic helix-loop-helix-leucine zipper (bHLH-ZIP) protein family activates target genes in heterodimeric association with another bHLH-ZIP protein, Max. Max readily homodimerizes, competes with C-myc-Max heterodimers, and represses transcription. Four additional bHLH-ZIP proteins, Mad1, Mxi1, Mad3 and Mad4, heterodimerize with Max and also repress transcription of c-myc-responsive genes. We employed a yeast two-hybid approach to identify proteins which interact with Mxi. We identified a novel ZIP-containing protein, Mmip1 (Mad member-interacting protein 1) that strongly dimerizes with all four Mad members, but not with c-myc, Max, or with unrelated HLH proteins. The Mmip1-Mxi association is mediated by the ZIP domain of each polypeptide and is as strong or stronger than the associations between c-myc and Max or Max and Mxi1. In vitro, Mmip1 can inhibit DNA binding by Max-Mad heterodimers and, in vivo, can reverse the suppressive effects of Mad proteins on c-myc functions. Mmipl is found in a variety of cells types, is induced by serum stimulation, and can be co-immunoprecipitated from fibroblasts in association with Mxi1. By interfering with the dimerization between Max and Mad family member proteins, Mmip1 can indirectly up-regulate the transcriptional activity of c-myc and suppress the antiproliferative actions of Mad proteins.
Gupta
K
K
Section of Hematology/Oncology, Childrens Hospital of Pittsburgh, Pennsylvania 15213, USA.
Anand
G
G
Yin
X
X
Grove
L
L
Prochownik
E V
EV
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D018797:Cell Cycle Proteins; D002460:Cell Line; D002522:Chlorocebus aethiops; D011508:Chondroitin Sulfate Proteoglycans; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D005347:Fibroblasts; D016259:Genes, myc; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D012097:Repressor Proteins; D014157:Transcription Factors / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D014162:Transfection; D025521:Tumor Suppressor Proteins
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D018797:Cell Cycle Proteins; D011508:Chondroitin Sulfate Proteoglycans; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D016271:Proto-Oncogene Proteins c-myc; D011994:Recombinant Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; C079439:MXD1 protein, human; C079440:MXI1 protein, human; C492318:SMC3 protein, human