The Nrf3 transcription factor is a membrane-bound glycoprotein targeted to the endoplasmic reticulum through its N-terminal homology box 1 sequence.
Transcription factor Nrf3 (NF-E2 p45-related factor 3) is targeted to the endoplasmic reticulum (ER). Mouse Nrf3 is subject to proteolysis, Asn glycosylation, and deglycosylation reactions. It is synthesized as a approximately 96-kDa protein that is subsequently converted into isoforms of approximately 90, 80, and 70 kDa. In the ER, the approximately 90-kDa glycoprotein is predominant and gives rise to approximately 80- and approximately 70-kDa isoforms. The approximately 90- and approximately 80-kDa polypeptides were observed in the nuclear envelope, whereas the approximately 70-kDa isoform was detected primarily in the nucleoplasm. Our experiments showed the N-terminal homology box 1 (NHB1, residues 12-31) is part of a tripartite signal peptide sequence, comprising n, h, and c regions. The h region (residues 12-23) was demonstrated to target Nrf3 to the ER and is necessary for its Asn glycosylation. The n region (residues 1-11) controlled the abundance of the approximately 90-kDa glycoprotein. The c region (residues 24-39) was found to contain a signal peptidase cleavage site that is responsible for production of the approximately 90-kDa mature Nrf3 glycoprotein from a approximately 96-kDa precursor. We have found that Nrf3 is activated by the ER stressors tunicamycin and brefeldin A, and that NHB1 is required for this response. Amino acids between the c region and NHB2 (residues 76-100) controlled the proteolytic processing of mouse Nrf3 into cleavage products of approximately 80-kDa (glycated) and approximately 70-kDa (non-glycated); by contrast, human Nrf3 lacked a signal peptidase cleavage site between its c region and NHB2. Lastly, data are presented suggesting that the NHB2 sequence in mouse Nrf3 may regulate the topology of the transcription factor within the ER membrane.
Zhang
Yiguo
Y
Biomedical Research Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom. Electronic address: y.z.zhang@dundee.ac.uk.
Kobayashi
Akira
A
Department of Medical Biochemistry, Tohoku University School of Medicine, Sendai 980-8575, Japan.
Yamamoto
Masayuki
M
Department of Medical Biochemistry, Tohoku University Graduate School of Medicine, Sendai 980-8577, Japan; Center for Tsukuba Advanced Research Alliance, University of Tsukuba, Tsukuba 305-8577, Japan.
Hayes
John D
JD
Biomedical Research Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, Scotland, United Kingdom.
D000595:Amino Acid Sequence; D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D019556:COS Cells; D002522:Chlorocebus aethiops; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D034741:RNA, Small Interfering; D017386:Sequence Homology, Amino Acid; D013347:Subcellular Fractions / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology
D050976:Basic-Leucine Zipper Transcription Factors; D008562:Membrane Glycoproteins; C485120:Nrf3 protein, mouse; D034741:RNA, Small Interfering