ABSTRACT
Zhangfei (ZF) is a basic region-leucine zipper protein that has been implicated in herpesvirus infection cycle and related cellular processes. Here we show both in vivo and in vitro data demonstrating that ZF is a novel cellular binding partner of activating transcription factor 4 (ATF4) (or CREB2). We found that ZF competed with ATF4 to form ATF4-ZF heterodimeric complexes through the bZIP regions. ZF enhanced ATF4 binding to the cAMP response element (CRE), and augmented activation of a CRE reporter by ATF4, in response to MEK1 activation. These results suggest an important role of ZF in the MEK1-ATF4 signaling pathway.
Subject(s)
Activating Transcription Factor 4/metabolism , Basic-Leucine Zipper Transcription Factors/metabolism , MAP Kinase Kinase 1/metabolism , MAP Kinase Signaling System/physiology , Response Elements/physiology , Activating Transcription Factor 4/genetics , Basic-Leucine Zipper Transcription Factors/genetics , Cyclic AMP/metabolism , HeLa Cells , Herpesviridae/genetics , Herpesviridae/metabolism , Herpesviridae Infections/genetics , Herpesviridae Infections/metabolism , Humans , MAP Kinase Kinase 1/genetics , Nuclear Proteins , Protein Structure, Tertiary/physiology , RNA-Binding Proteins , Transcription Factors , Virus Replication/physiologyABSTRACT
Zhangfei is a basic region-leucine zipper (bZIP) transcription factor identified through its interaction with a herpesvirus-related host cell factor HCF1 (C1). Unlike most bZIP proteins, the mammalian Zhangfei protein does not bind DNA as homodimers. It is believed due to the absence of an asparagine residue in the basic region, which forms the DNA-recognition motif, NxxAAxxCR, in all bZIP proteins. Here, we report the identification and characterization of a novel Zhangfei homologue in Takifugu rubripes, which has an intact DNA-recognition motif by sequence analysis. We found that the pufferfish Zhangfei (pZF) appeared to have all the functional domains known in human Zhangfei, including the conserved HCF1-binding motif; however, pZF did not appear to bind DNA either. These findings suggest that the distinct property of the Zhangfei basic region is conserved during the evolution of vertebrates and that Zhangfei requires interaction with other proteins to regulate transcription from target promoters.
Subject(s)
Basic-Leucine Zipper Transcription Factors/chemistry , Basic-Leucine Zipper Transcription Factors/metabolism , DNA/chemistry , DNA/metabolism , Tetraodontiformes/metabolism , Amino Acid Sequence , Animals , Basic-Leucine Zipper Transcription Factors/genetics , Binding Sites , Conserved Sequence , DNA/genetics , Humans , Molecular Sequence Data , Protein Binding , Sequence Homology, Amino Acid , Tetraodontiformes/geneticsABSTRACT
Luman (or LZIP, CREB3) is a transcription factor with an endoplasmic reticulum (ER)-transmembrane domain. Due to its structural similarities with ATF6, it is thought that Luman might also be involved in cellular stress responses. Here we report that Luman can bind and activate transcription from the consensus unfolded protein response element (UPRE). Mutations that disrupted the binding of Luman to the UPREs impaired its ability to activate transcription from these sites. Overexpression of Luman stimulated transcription of EDEM, a downstream effector of the mammalian unfolded protein response involved in ER-associated degradation (ERAD). Unlike ATF6, however, Luman was not activated by proteolytic cleavage in response to endoplasmic reticulum stressors such as tunicamycin and thapsigargin. These results suggest that the activation of ERAD by Luman is likely through a pathway different from the common ER stress response, and that additional factor(s) are required for the activation of this Luman-mediated pathway.
