Zhangfei Is a Potent and Specific Inhibitor of the Host Cell Factor-binding Transcription Factor Luman

Abstract

Host cell factor (HCF) was initially discovered as a cellular co-factor required for the activation of herpes simplex virus immediate early gene expression by the virion associated transactivator VP16. HCF also participates in a variety of cellular processes, although the mechanism of its action is not known. VP16 binds to HCF through a 4-amino acid motif (EHAY), which closely resembles the HCF binding domain of two cellular basic leucine-zipper proteins, Luman and Zhangfei. Luman is a powerful transcription factor that, in transient expression assays, activates promoters containing cAMP or unfolded protein response elements (UPRE). In contrast, Zhangfei neither binds consensus recognition elements for basic leucinezipper proteins nor does it activate promoters containing them. Here we show that Zhangfei suppresses the ability of Luman to activate transcription. HCF appeared to be required for efficient suppression. A mutant of Zhangfei, which was unable to bind HCF, was impaired in its ability to suppress Luman. Zhangfei did not suppress ATF6, a transcription factor closely related to Luman but that does not bind HCF, unless the HCF binding motif of Luman was grafted onto it. Zhangfei inhibited the HCF-dependent activation of a UPRE-containing promoter by a Gal4-Luman fusion protein but was unable to inhibit the HCF-independent activation by Gal4-Luman of a promoter that contained Gal4 binding motifs. Binding of HCF by Zhangfei was required for the co-localization of Luman and Zhangfei to nuclear domains, suggesting that HCF might target the proteins to a common location.

The Neuronal Host Cell Factor-Binding Protein Zhangfei Inhibits Herpes Simplex Virus Replication

“…In contrast, Zhangfei does not bind any of the known cognate sequences for b-zip proteins, nor does it activate promoters containing these sequences (23). However, Zhangfei has a profoundly repressive effect upon HCF-dependent transcription activation by Luman (30). HCF binding by both Zhangfei and Luman is required for efficient suppression by Zhangfei.…”

“…The plasmids encoding Zhangfei (pcZF); mutant Zhangfei which is unable to bind HCF (pcZF Y224A); LuS221Op, the truncated form of full-length Luman (pcLuS221Op); LuS221Op (N160G) with a mutation in the DNA binding domain (pcLuS221Op N160G); and HCF (pSL7) have been previously described (19,23,30). The plasmid G5EC, a chloramphenicol acetyltransferase (CAT) reporter which contains five copies of the Saccharomyces cerevisiae Gal4 upstream activation signal (UAS), as well as the pM series of plasmids for constructing Gal4 fusion proteins was a gift from Ivan Sadowski.…”

“…Recombinant adenovirus vectors were constructed as described earlier (30). HSV-1 stock (KOS strain) was propagated in Vero cells.…”

“…Luman activates promoters containing cyclic AMP and unfolded protein response elements (CRE and UPRE) (25,30). In contrast, Zhangfei does not bind any of the known cognate sequences for b-zip proteins, nor does it activate promoters containing these sequences (23).…”

Insulin-Inducible SMILE Inhibits Hepatic Gluconeogenesis

“…However, SMILE cannot bind to DNA as a homodimer (10)(11)(12). SMILE has also been reported to function as a coactivator of activating transcription factor 4 or as a corepressor of host cell factor-binding transcription factor (13,14). Previously, we have reported that SMILE is a corepressor of the estrogen receptor-related receptor g, glucocorticoid receptor (GR), constitutive androstane receptor, hepatocyte nuclear factor 4a (HNF4a), and CREBH (15)(16)(17).…”