Molecular determinants for small Maf protein control of platelet production.
MafG and p45 possess basic region-leucine zipper (bZip) domains and form a heterodimer called NF-E2, a key regulator of megakaryopoiesis. NF-E2 binds to the Maf recognition element (MARE) and activates transcription of many platelet genes. Since the bZip domain, which mediates DNA binding and heterodimerization, is the only functional domain established for MafG, it has been assumed that MafG is required only for p45 binding to MARE and to facilitate p45-mediated transcriptional activation. Analysis of the C-terminal region of MafG, which is distinct from the bZip domain, revealed that this region contains a nuclear matrix-targeting signal. We used a transgenic complementation rescue assay to delineate the function of the MafG C terminus in vivo. Transgenic mice expressing a mutant MafG protein lacking the C terminus (MafGΔC) were crossed into a MafG-null background. The compound mutant mice displayed severe thrombocytopenia and splenomegaly, which phenocopied p45-null mice. The MafG C terminus is essential for proplatelet formation and platelet gene activation but not for p45 binding to MARE. These results demonstrate that the MafG C terminus is required for NF-E2 function and suggest that efficient targeting of NF-E2 to a specific nuclear scaffold is important to achieve high-level activity.
Center for Radioisotope Sciences, Tohoku University Graduate School of Medicine, 2-1 Seiryo-cho, Aoba-ku, Sendai 980-8575, Japan. hozumim@med.tohoku.ac.jp
Hozumi
H
Motohashi
Rie
R
Fujita
Mariko
M
Takayama
Ai
A
Inoue
Fumiki
F
Katsuoka
Emery H
EH
Bresnick
Masayuki
M
Yamamoto
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D002460:Cell Line; D017124:Conserved Sequence; D017931:DNA Primers / Q000235:genetics; D006801:Humans; D050978:Maf Transcription Factors, Small / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D051259:MafG Transcription Factor / Q000737:chemistry / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D008533:Megakaryocytes / Q000166:cytology / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008954:Models, Biological; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050984:NF-E2 Transcription Factor, p45 Subunit / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D034061:Thrombopoiesis / Q000235:genetics / Q000502:physiology*; D015533:Transcriptional Activation
D017931:DNA Primers; D050978:Maf Transcription Factors, Small; D051259:MafG Transcription Factor; C491247:Mafg protein, mouse; D050505:Mutant Proteins; D050984:NF-E2 Transcription Factor, p45 Subunit; C494693:Nfe2 protein, mouse; D012097:Repressor Proteins