The transcriptional regulator Zfat is essential for maintenance and differentiation of the adipocytes

Adipocytes play crucial roles in the control of whole‐body energy homeostasis. Differentiation and functions of the adipocytes are regulated by various transcription factors. Zfat (zinc‐finger protein with AT‐hook) is a transcriptional regulator that controls messenger RNA expression of specific genes through binding to their transcription start sites. Here we report important roles of Zfat in the adipocytes. We establish inducible Zfat‐knockout (Zfat iKO) mice where treatment with tamoxifen causes a marked reduction in Zfat expression in various tissues. Tamoxifen treatment of Zfat iKO mice reduces the white adipose tissues (WATs) mass, accompanied by the decreased triglyceride levels. Zfat is expressed in both the adipose‐derived stem cells (ADSCs) and mature adipocytes in the WATs. In ex vivo assays of the mature adipocytes differentiated from the Zfat iKO ADSCs, loss of Zfat in the mature adipocytes reduces the triglyceride levels, suggesting cell autonomous roles of Zfat in the maintenance of the mature adipocytes. Furthermore, we identify the Atg13, Brf1, Psmc3, and Timm22 genes as Zfat‐target genes in the mature adipocytes. In contrast, loss of Zfat in the ADSCs impairs adipocyte differentiation with the decreased expression of C/EBPα and adiponectin. Thus, we propose that Zfat plays crucial roles in maintenance and differentiation of the adipocytes.

Zfat Is Indispensable for the Development of Erythroid Cells in the Fetal Liver

BACKGROUND/AIM

In mice, fetal liver is the first tissue of definitive erythropoiesis for definitive erythroid expansion and maturation. ZFAT, originally identified as a candidate susceptibility gene for autoimmune thyroid disease, has been reported to be involved in primitive hematopoiesis and T cell development. The aim of this study was to examine whether or not Zfat is involved in definitive erythropoiesis in the fetal liver during mammalian development.

MATERIALS AND METHODS

The role of Zfat during mouse fetal erythropoiesis in the fetal liver was examined using tamoxifen-inducible CreERT2 Zfat-deficient mice.

RESULTS

Zfat-deficient mice exhibit moderate anemia with small and pale fetal liver through a decreased number of erythroblasts by E12.5. Apoptosis sensitivity in fetal liver erythroid progenitors was enhanced by Zfat-deficiency ex vivo. Moreover, Zfat knockdown partially inhibited CD71^-/lowTer119^- to CD71^highTer119^- transition of fetal liver erythroid progenitors with impairment in the elevation of CD71 expression.

CONCLUSION

Zfat plays a critical role for erythropoiesis in the fetal liver.

Molecular mechanisms of transcriptional regulation by the nuclear zinc-finger protein Zfat in T cells

Zfat is a nuclear protein with AT-hook and zinc-finger domains. We previously reported that Zfat plays crucial roles in T-cell survival and development in mice. However, the molecular mechanisms whereby Zfat regulates gene expression in T cells remain unexplored. In this study, we analyzed the genome-wide occupancy of Zfat by chromatin immunoprecipitation with sequencing (ChIP-seq), which showed that Zfat bound predominantly to a region around a transcription start site (TSS), and that an 8-bp nucleotide sequence GAA(T/A)(C/G)TGC was identified as a consensus sequence for Zfat-binding sites. Furthermore, about half of the Zfat-binding sites were characterized by histone H3 acetylations at lysine 9 and lysine 27 (H3K9ac/K27ac). Notably, Zfat gene deletion decreased the H3K9ac/K27ac levels at the Zfat-binding sites, suggesting that Zfat may be related to the regulation of H3K9ac/K27ac. Integrated analysis of ChIP-seq and transcriptional profiling in thymocytes identified Zfat-target genes with transcription to be regulated directly by Zfat. We then focused on the chromatin regulator Brpf1, a Zfat-target gene, revealing that Zfat bound directly to a 9-bp nucleotide sequence, CGAANGTGC, which is conserved among mammalian Brpf1 promoters. Furthermore, retrovirus-mediated re-expression of Zfat in Zfat-deficient peripheral T cells restored Brpf1 expression to normal levels, and shRNA-mediated Brpf1 knockdown in peripheral T cells increased the proportion of apoptotic cells, suggesting that Zfat-regulated Brpf1 expression was important for T-cell survival. Our findings demonstrated that Zfat regulates the transcription of target genes by binding directly to the TSS proximal region, and that Zfat-target genes play important roles in T-cell homeostasis.

The Nuclear Zinc Finger Protein Zfat Maintains FoxO1 Protein Levels in Peripheral T Cells by Regulating the Activities of Autophagy and the Akt Signaling Pathway

Forkhead box O1 (FoxO1) is a key molecule for the development and functions of peripheral T cells. However, the precise mechanisms regulating FoxO1 expression in peripheral T cells remain elusive. We previously reported that Zfat(f/f)-CD4Cre mice showed a marked decline in FoxO1 protein levels in peripheral T cells, partially through proteasomal degradation. Here we have identified the precise mechanisms, apart from proteasome-mediated degradation, of the decreased FoxO1 levels in Zfat-deficient T cells. First, we confirmed that tamoxifen-inducible deletion of Zfat in Zfat(f/f)-CreERT2 mice coincidently decreases FoxO1 protein levels in peripheral T cells, indicating that Zfat is essential for maintaining FoxO1 levels in these cells. Although the proteasome-specific inhibitors lactacystin and epoxomicin only moderately increase FoxO1 protein levels, the inhibitors of lysosomal proteolysis bafilomycin A1 and chloroquine restore the decreased FoxO1 levels in Zfat-deficient T cells to levels comparable with those in control cells. Furthermore, Zfat-deficient T cells show increased numbers of autophagosomes and decreased levels of p62 protein, together indicating that Zfat deficiency promotes lysosomal FoxO1 degradation through autophagy. In addition, Zfat deficiency increases the phosphorylation levels of Thr-308 and Ser-473 of Akt and the relative amounts of cytoplasmic to nuclear FoxO1 protein levels, indicating that Zfat deficiency causes Akt activation, leading to nuclear exclusion of FoxO1. Our findings have demonstrated a novel role of Zfat in maintaining FoxO1 protein levels in peripheral T cells by regulating the activities of autophagy and the Akt signaling pathway.

Marked Reduction in FoxO1 Protein by its Enhanced Proteasomal Degradation in Zfat-deficient Peripheral T-Cells

BACKGROUND

Zfat is a nuclear protein that harbours putative DNA-binding domains. T-cell specific deletion of Zfat in Zfat(f/f)-CD4Cre mice yields a significant decrease in the number of peripheral T-cells with a lower surface expression of interleukin-7 receptor-α (IL-7Rα). However, the molecular mechanism by which Zfat controls IL-7Rα expression remains unknown.

MATERIALS AND METHODS

Expression levels of the molecules involved in IL-7Rα expression were determined by immunoblotting.

RESULTS

Zfat-deficient peripheral T-cells showed a marked reduction in the FoxO1 protein that regulates IL-7Rα expression; however, the FoxO1 mRNA expression level was not affected by Zfat-deficiency. Furthermore, treatment of Zfat-deficient T-cells with a proteasome inhibitor, epoxomicin, restored FoxO1 expression levels, indicating that the loss of Zfat enhanced the proteasomal degradation of the FoxO1 protein.

CONCLUSION

These results suggest that Zfat is required for peripheral T-cell homeostasis through IL-7Rα expression by controlling the FoxO1 protein.