CREBZF, a novel Smad8-binding protein

Formononetin Derivative for Osteoporosis by Simultaneous Regulating Osteoblast and Osteoclast

Seven new formononetin derivatives (1-7) were designed and prepared from formononetin (phase II phytoestrogen). The derivatives 9-butyl-3-(4-methoxyphenyl)-9,10-dihydro-4H,8H-chromeno[8,7-e][1,3]oxazin-4-one (2) and 9-(furan-3-ylmethyl)-3-(4-methoxyphenyl)-9,10-dihydro-4H,8H-chromeno[8,7-e][1,3]oxazin-4-one (7) promoted significant osteoblast formation by modulating the BMP/Smad pathway. Compound 7 exhibited potent antiosteoclastogenesis activity in RANKL-induced RAW264.7 cells and ovariectomy (OVX)-induced osteoporosis in mice by regulation of the RANK/RANKL/OPG pathway. Compound 7 regulated osteoblast and osteoclast simultaneously and showed better effect than the well-known drug ipriflavone in vivo, suggesting 7 as a patented antiosteoporosis candidate.

Emerging Role of SMILE in Liver Metabolism

Small heterodimer partner-interacting leucine zipper (SMILE) is a member of the CREB/ATF family of basic leucine zipper (bZIP) transcription factors. SMILE has two isoforms, a small and long isoform, resulting from alternative usage of the initiation codon. Interestingly, although SMILE can homodimerize similar to other bZIP proteins, it cannot bind to DNA. As a result, SMILE acts as a co-repressor in nuclear receptor signaling and other transcription factors through its DNA binding inhibition, coactivator competition, and direct repression, thereby regulating the expression of target genes. Therefore, the knockdown of SMILE increases the transactivation of transcription factors. Recent findings suggest that SMILE is an important regulator of metabolic signals and pathways by causing changes in glucose, lipid, and iron metabolism in the liver. The regulation of SMILE plays an important role in pathological conditions such as hepatitis, diabetes, fatty liver disease, and controlling the energy metabolism in the liver. This review focuses on the role of SMILE and its repressive actions on the transcriptional activity of nuclear receptors and bZIP transcription factors and its effects on liver metabolism. Understanding the importance of SMILE in liver metabolism and signaling pathways paves the way to utilize SMILE as a target in treating liver diseases.

Emerging Role of SMILE in Liver Metabolism

Small heterodimer partner-interacting leucine zipper (SMILE) is a member of the CREB/ATF family of basic leucine zipper (bZIP) transcription factors. SMILE has two isoforms, a small and long isoform, resulting from alternative usage of the initiation codon. Interestingly, although SMILE can homodimerize similar to other bZIP proteins, it cannot bind to DNA. As a result, SMILE acts as a co-repressor in nuclear receptor signaling and other transcription factors through its DNA binding inhibition, coactivator competition, and direct repression, thereby regulating the expression of target genes. Therefore, the knockdown of SMILE increases the transactivation of transcription factors. Recent findings suggest that SMILE is an important regulator of metabolic signals and pathways by causing changes in glucose, lipid, and iron metabolism in the liver. The regulation of SMILE plays an important role in pathological conditions such as hepatitis, diabetes, fatty liver disease, and controlling the energy metabolism in the liver. This review focuses on the role of SMILE and its repressive actions on the transcriptional activity of nuclear receptors and bZIP transcription factors and its effects on liver metabolism. Understanding the importance of SMILE in liver metabolism and signaling pathways paves the way to utilize SMILE as a target in treating liver diseases.

CREBZF regulates testosterone production in mouse Leydig cells

CREBZF, including the two isoforms SMILE (long isoform of CREBZF) and Zhangfei (short isoform of CREBZF), has been identified as a novel transcriptional coregulator of a variety of nuclear receptors. Our previous studies found that SMILE is expressed in the mouse uterine luminal and glandular epithelium and is upregulated by estrogen. In the present study, CREBZF was age-dependently and -specifically expressed in mouse interstitial Leydig cells during sexual maturation. The expression pattern of CREBZF exhibited an age-related increase, and SMILE was the dominant isoform in the mouse testis. Although hCG did not affect CREBZF expression, CREBZF silencing significantly inhibited hCG-stimulated testosterone production in primary Leydig cells and MLTC-1 cells. Meanwhile, the serum concentration of testosterone was significantly decreased after microinjection of lentiviral-mediated shRNA-CREBZF into the mature mouse testis. In addition, CREBZF silencing markedly decreased P450c17, 17β-HSD, and 3β-HSD expression following hCG stimulation in primary Leydig cells, and this inhibitory effect was obviously reversed by overexpression of CREBZF. Furthermore, CREBZF significantly upregulated the mRNA levels of Nr4a1 and Nr5a1, which are the essential orphan nuclear receptors for steroidogenic gene expression. Together our data indicate that CREBZF promotes hCG-induced testosterone production in mouse Leydig cells by affecting Nr4a1 and Nr5a1 expression levels and subsequently increasing the expression of steroidogenic genes such as 3β-HSD, 17β-HSD, and P450c17, suggesting a potential important role of CREBZF in testicular testosterone synthesis.

Activation of CREBZF Increases Cell Apoptosis in Mouse Ovarian Granulosa Cells by Regulating the ERK1/2 and mTOR Signaling Pathways

CREBZF, a multifunction transcriptional regulator, participates in the regulation of numerous cellular functions. The aims of the present study were to detect the localization of CREBZF expression in the ovary and explore the role of CREBZF and related mechanisms in the apoptosis of ovarian granulosa cells. We found by immunohistochemistry that CREBZF was mainly located in granulosa cells and oocytes during the estrous cycle. Western blot analysis showed that SMILE was the main isoform of CREBZF in the ovary. The relationship between apoptosis and CREBZF was assessed via CREBZF overexpression and knockdown. Flow cytometry analysis showed that CREBZF induced cell apoptosis in granulosa cells. Western bolt analysis showed that overexpression of CREBZF upregulated BAX and cleaved Caspase-3, while it downregulated BCL-2. Furthermore, overexpression of CREBZF inhibited the ERK1/2 and mTOR signaling pathways through the phosphorylation of intracellular-regulated kinases 1/2 (ERK1/2) and p70 S6 kinase (S6K1). Moreover, we found that CREBZF also activated autophagy by increasing LC3-II. In summary, these results suggest that CREBZF might play a proapoptotic role in cell apoptosis in granulosa cells, possibly by regulating the ERK1/2 and mTOR signaling pathways.

Transcriptome analysis reveals long intergenic non-coding RNAs involved in skeletal muscle growth and development in pig

Long intergenic non-coding RNAs (lincRNAs) play essential roles in numerous biological processes and are widely studied. The skeletal muscle is an important tissue that plays an essential role in individual movement ability. However, lincRNAs in pig skeletal muscles are largely undiscovered and their biological functions remain elusive. In this study, we assembled transcriptomes using RNA-seq data published in previous studies of our laboratory group and identified 323 lincRNAs in porcine leg muscle. We found that these lincRNAs have shorter transcript length, fewer exons and lower expression level than protein-coding genes. Gene ontology and pathway analyses indicated that many potential target genes (PTGs) of lincRNAs were involved in skeletal-muscle-related processes, such as muscle contraction and muscle system process. Combined our previous studies, we found a potential regulatory mechanism in which the promoter methylation of lincRNAs can negatively regulate lincRNA expression and then positively regulate PTG expression, which can finally result in abnormal phenotypes of cloned piglets through a certain unknown pathway. This work detailed a number of lincRNAs and their target genes involved in skeletal muscle growth and development and can facilitate future studies on their roles in skeletal muscle growth and development.

Insulin-Inducible SMILE Inhibits Hepatic Gluconeogenesis

The role of a glucagon/cAMP-dependent protein kinase-inducible coactivator PGC-1α signaling pathway is well characterized in hepatic gluconeogenesis. However, an opposing protein kinase B (PKB)/Akt-inducible corepressor signaling pathway is unknown. A previous report has demonstrated that small heterodimer partner-interacting leucine zipper protein (SMILE) regulates the nuclear receptors and transcriptional factors that control hepatic gluconeogenesis. Here, we show that hepatic SMILE expression was induced by feeding in normal mice but not in db/db and high-fat diet (HFD)-fed mice. Interestingly, SMILE expression was induced by insulin in mouse primary hepatocyte and liver. Hepatic SMILE expression was not altered by refeeding in liver-specific insulin receptor knockout (LIRKO) or PKB β-deficient (PKBβ(-/-)) mice. At the molecular level, SMILE inhibited hepatocyte nuclear factor 4-mediated transcriptional activity via direct competition with PGC-1α. Moreover, ablation of SMILE augmented gluconeogenesis and increased blood glucose levels in mice. Conversely, overexpression of SMILE reduced hepatic gluconeogenic gene expression and ameliorated hyperglycemia and glucose intolerance in db/db and HFD-fed mice. Therefore, SMILE is an insulin-inducible corepressor that suppresses hepatic gluconeogenesis. Small molecules that enhance SMILE expression would have potential for treating hyperglycemia in diabetes.

The effect of Zhangfei/CREBZF on cell growth, differentiation, apoptosis, migration, and the unfolded protein response in several canine osteosarcoma cell lines

Background

We had previously shown that the bLZip domain-containing transcription factor, Zhangfei/CREBZF inhibits the growth and the unfolded protein response (UPR) in cells of the D–17 canine osteosarcoma (OS) line and that the effects of Zhangfei are mediated by it stabilizing the tumour suppressor protein p53. To determine if our observations with D-17 cells applied more universally to canine OS, we examined three other independently isolated canine OS cell lines—Abrams, McKinley and Gracie.

Results

Like D–17, the three cell lines expressed p53 proteins that were capable of activating promoters with p53 response elements on their own, and synergistically with Zhangfei. Furthermore, as with D–17 cells, Zhangfei suppressed the growth and UPR-related transcripts in the OS cell lines. Zhangfei also induced the activation of osteocalcin expression, a marker of osteoblast differentiation and triggered programmed cell death.

Conclusions

Osteosarcomas are common malignancies in large breeds of dogs. Although there has been dramatic progress in their treatment, these therapies often fail, leading to recurrence of the tumour and metastatic spread. Our results indicate that induction of the expression of Zhangfei in OS, where p53 is functional, may be an effective modality for the treatment of OS.

Ursodeoxycholic acid inhibits liver X receptor α-mediated hepatic lipogenesis via induction of the nuclear corepressor SMILE

Small heterodimer partner interacting leucine zipper protein (SMILE) has been identified as a nuclear corepressor of the nuclear receptor (NRs) family. Here, we examined the role of SMILE in the regulation of nuclear receptor liver X receptor (LXR)-mediated sterol regulatory element binding protein-1c (SREBP-1c) gene expression. We found that SMILE inhibited T0901317 (T7)-induced transcriptional activity of LXR, which functions as a major regulator of lipid metabolism by inducing SREBP-1c, fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) gene expression. Moreover, we demonstrated that SMILE physically interacts with LXR and represses T7-induced LXR transcriptional activity by competing with coactivator SRC-1. Adenoviral overexpression of SMILE (Ad-SMILE) attenuated fat accumulation and lipogenic gene induction in the liver of T7 administered or of high fat diet (HFD)-fed mice. Furthermore, we investigated the mechanism by which ursodeoxycholic acid (UDCA) inhibits LXR-induced lipogenic gene expression. Interestingly, UDCA treatment significantly increased SMILE promoter activity and gene expression in an adenosine monophosphate-activated kinase-dependent manner. Furthermore, UDCA treatment repressed T7-induced SREBP-1c, FAS, and ACC protein levels, whereas knockdown of endogenous SMILE gene expression by adenovirus SMILE shRNA (Ad-shSMILE) significantly reversed UDCA-mediated repression of SREBP-1c, FAS, and ACC protein levels. Collectively, these results demonstrate that UDCA activates SMILE gene expression through adenosine monophosphate-activated kinase phosphorylation, which leads to repression of LXR-mediated hepatic lipogenic enzyme gene expression.

Effects of cyclic AMP response element binding protein-Zhangfei (CREBZF) on the unfolded protein response and cell growth are exerted through the tumor suppressor p53

Zhangfei/CREBZF, a basic region-leucine zipper (bLZip) transcription factor, is a potent suppressor of growth and the unfolded protein response (UPR) in some cancer cell lines, including the canine osteosarcoma cell line, D-17. However, the effects of Zhangfei are not universal, and it has no obvious effects on untransformed cells and some cancer cell lines, suggesting that Zhangfei may act through an intermediary that is either not induced or is defective in cells that it does not affect. Here we identify the tumor suppressor protein p53 as this intermediary. We show the following: in cells ectopically expressing Zhangfei, the protein stabilizes p53 and co-localizes with it in cellular nuclei; the bLZip domain of Zhangfei is required for its profound effects on cell growth and interaction with p53. Suppression of p53 by siRNA at least partially inhibits the effects of Zhangfei on the UPR and cell growth. The effects of Zhangfei on D-17 cells is mirrored by its effects on the p53-expressing human osteosarcoma cell line U2OS, while Zhangfei has no effect on the p53-null osteosarcoma cell line MG63. In U2OS cells, Zhangfei displaces the E3 ubiquitin ligase mouse double minute homolog 2 (Mdm2) from its association with p53, suggesting a mechanism for the effects of Zhangfei on p53.

Zhangfei/CREB-ZF - a potential regulator of the unfolded protein response

Cells respond to perturbations in the microenvironment of the endoplasmic reticulum (ER), and to the overloading of its capacity to process secretory and membrane-associate proteins, by activating the Unfolded Protein Response (UPR). Genes that mediate the UPR are regulated by three basic leucine-zipper (bLZip) motif-containing transcription factors – Xbp1s, ATF4 and ATF6. A failure of the UPR to achieve homeostasis and its continued stimulation leads to apoptosis. Mechanisms must therefore exist to turn off the UPR if it successfully restores normalcy. The bLZip protein Zhangfei/CREBZF/SMILE is known to suppress the ability of several, seemingly structurally unrelated, transcription factors. These targets include Luman/CREB3 and CREBH, ER-resident bLZip proteins known to activate the UPR in some cell types. Here we show that Zhangfei had a suppressive effect on most UPR genes activated by the calcium ionophore thapsigargin. This effect was at least partially due to the interaction of Zhangfei with Xbp1s. The leucine zipper of Zhangfei was required for this interaction, which led to the subsequent proteasomal degradation of Xbp1s. Zhangfei suppressed the ability of Xbp1s to activate transcription from a promoter containing unfolded protein response elements and significantly reduced the ability to Xbp1s to activate the UPR as measured by RNA and protein levels of UPR-related genes. Finally, specific suppression of endogenous Zhangfei in thapsigargin-treated primary rat sensory neurons with siRNA directed to Zhangfei transcripts, led to a significant increase in transcripts and proteins of UPR genes, suggesting a potential role for Zhangfei in modulating the UPR.