Altered energy homeostasis and resistance to diet-induced obesity in KRAP-deficient mice.

Obesity and related metabolic disorders have become leading causes of adult morbidity and mortality. KRAP (Ki-ras-induced actin-interacting protein) is a cytoskeleton-associated protein and a ubiquitous protein among tissues, originally identified as a cancer-related molecule, however, its physiological roles remain unknown. Here we demonstrate that KRAP-deficient (KRAP(-/-)) mice show enhanced metabolic rate, decreased adiposity, improved glucose tolerance, hypoinsulinemia and hypoleptinemia. KRAP(-/-) mice are also protected against high-fat diet-induced obesity and insulin resistance despite of hyperphagia. Notably, glucose uptake in the brown adipose tissue (BAT) in KRAP(-/-) mice is enhanced in an insulin-independent manner, suggesting that BAT is involved in altered energy homeostasis in KRAP(-/-) mice, although UCP (Uncoupling protein) expressions are not altered. Of interest is the down-regulation of fatty acid metabolism-related molecules, including acetyl-CoA carboxylase (ACC)-1, ACC-2 and fatty acid synthase in the liver of KRAP(-/-) mice, which could in part account for the metabolic phenotype in KRAP(-/-) mice. Thus, KRAP is a novel regulator in whole-body energy homeostasis and may be a therapeutic target in obesity and related diseases.

ZFAT expression in B and T lymphocytes and identification of ZFAT-regulated genes.

The human ZFAT gene encodes a 1243-amino-acid protein containing one AT hook and 18 C2H2 zinc finger domains, which are highly conserved among ZFAT orthologues from fish to mammalian species. Consistent with the presence of multiple predicted nuclear localization signals, endogenous ZFAT protein was found to be localized to the nucleus. In the mouse tissues examined by Western blotting, ZFAT was found to be expressed in thymus, spleen, and lymph nodes, but not in other tissues, including bone marrow. Furthermore, ZFAT protein was found to be up-regulated during the transition from CD4(-)CD8(-) to CD4(+)CD8(+) thymocytes and to be expressed only in B and T lymphocytes in peripheral lymphoid tissues. Expression array analyses demonstrated that genes that are down-regulated upon ZFAT overexpression in mouse Ba/F3 cells are significantly enriched for those functionally related to immune responses. These results suggest that ZFAT functions as a critical transcriptional regulator in B and T lymphocytes.

Analysis of KRAP expression and localization, and genes regulated by KRAP in a human colon cancer cell line.

We previously identified the human KRAP (Ki-ras-induced actin-interacting protein) gene from the cDNA library of human colon cancer HCT116 cells as one of the genes whose expression levels were up-regulated by activated Ki-ras. Although the KRAP gene is structurally conserved from fish to mammalian species, the expression pattern and function of KRAP still remain to be elucidated. Here, we have generated a specific polyclonal antibody for KRAP and characterized the histological expression of KRAP in mouse tissues. KRAP was ubiquitously expressed in mouse tissues, with high levels in pancreas, liver, and brown adipose tissues, and KRAP was co-localized with filamentous actin along the apical membranes in both pancreas and liver tissues. A subfractionation study revealed that KRAP is a cytoplasmic protein and that the majority is associated with the cytoskeleton. Furthermore, microarray gene expression profile by inhibiting KRAP expression in HCT116 cells showed that several receptors and signal molecules frequently deregulated in cancers were differentially expressed in the KRAP-knockdown cells. All of these results suggested that KRAP might be a cytoskeleton-associated protein involving the structural integrity and/or signal transductions in human cancers.

Role of epiregulin in peptidoglycan-induced proinflammatory cytokine production by antigen presenting cells.

We have previously found that epiregulin, a member of epidermal growth factor superfamily, is involved in proinflammatory cytokine production in bone marrow-derived macrophages. In this report, to further assess the role of epiregulin in innate immunity, we measured IL-6 production levels upon lipopolysaccharide and peptidoglycan stimulation in antigen presenting cells including macrophages and dendritic cells. Our analyses using epiregulin-deficient mice with mixed and inbred genetic backgrounds revealed that epiregulin deficiency results in the reduction of IL-6 production levels in both cell types upon peptidoglycan stimulation, and that the extent of this reduction is more evident under the BALB/c background compared with the C57BL/6J background. These results indicated that epiregulin may have a critical role in the regulation of peptidoglycan-mediated proinflammatory cytokine production in antigen presenting cells and innate immunity.

Dermatitis due to epiregulin deficiency and a critical role of epiregulin in immune-related responses of keratinocyte and macrophage.

Epidermal growth factor (EGF) family members, including epiregulin (EP), play a fundamental role in epithelial tissues; however, their roles in immune responses and the physiological role of EP remain to be elucidated. The skin has a versatile system of immune surveillance. Biologically active IL-1alpha is released to extracellular space upon damage from keratinocytes and is a major player in skin inflammation. Here, we show that EP is expressed not only in keratinocytes but also in tissue-resident macrophages, and that EP-deficient (EP(-/-)) mice develop chronic dermatitis. Wound healing in the skin in EP(-/-) mice was not impaired in vivo, nor was the growth rate of keratinocytes from EP(-/-) mice different from that of WT mice in vitro. Of interest is that in WT keratinocytes, both IL-1alpha and the secreted form of EP induced down-regulation of IL-18 mRNA expression, which overexpression in the epidermis was reported to induce skin inflammation in mice, whereas the down-regulation of IL-18 induced by IL-1alpha was impaired in EP(-/-) keratinocytes. Although bone marrow transfer experiments indicated that EP deficiency in non-bone-marrow-derived cells is essential for the development of dermatitis, production of proinflammatory cytokines by EP(-/-) macrophages in response to Toll-like receptor agonists was much lower, compared with WT macrophages, whose dysfunction in EP(-/-) macrophages was not compensated by the addition of the secreted form of EP. These findings, taken together, suggested that EP plays a critical role in immune/inflammatory-related responses of keratinocytes and macrophages at the barrier from the outside milieu and that the secreted and membrane-bound forms of EP have distinct functions.

SNPs in the promoter of a B cell-specific antisense transcript, SAS-ZFAT, determine susceptibility to autoimmune thyroid disease.

Autoimmune thyroid disease (AITD) is caused by an immune response to self-thyroid antigens and has a significant genetic component. Antisense RNA transcripts have been implicated in gene regulation. Here we have identified a novel zinc-finger gene, designated ZFAT (zinc-finger gene in AITD susceptibility region), as one of the susceptibility genes in 8q23-q24 through an initial association analysis using the probands in the previous linkage analysis and a subsequent association analysis of the samples from a total of 515 affected individuals and 526 controls. The T allele of the single-nucleotide polymorphism (SNP), Ex9b-SNP10 located in the intron 9 of ZFAT, is associated with increased risk for AITD (dominant model: odds ratio = 1.7, P = 0.000091). The Ex9b-SNP10 falls into the 3'-UTR of truncated-ZFAT (TR-ZFAT) and the promoter region of the small antisense transcript of ZFAT (SAS-ZFAT). In peripheral blood lymphocytes, SAS-ZFAT is exclusively expressed in CD19+ B cells and expression levels of SAS-ZFAT and TR-ZFAT seemed to correlate with the Ex9b-SNP10-T-associated ZFAT-allele, inversely and positively, respectively. The Ex9b-SNP10 is critically involved in the regulation of SAS-ZFAT expression in vitro and this expression results in a decreased expression of TR-ZFAT. These results suggested that the SNP-associated ZFAT-allele plays a critical role in B cell function by affecting the expression level of TR-ZFAT through regulating SAS-ZFAT expression and that this novel regulatory mechanism of SNPs might be involved in controlling susceptibility or resistance to human disease.

Deregulated expression of KRAP, a novel gene encoding actin-interacting protein, in human colon cancer cells.

We have identified a novel gene, designated KRAP (Ki- ras-induced actin-interacting protein), encoding a protein of 1,259 amino acids with coiled-coil regions and transmembrane regions, from the cDNA library of human colon cancer HCT116 cells, as one of the genes upregulated by activated Ki- ras. While KRAP was rarely expressed in normal colon epithelium, deregulated constitutive KRAP expression was observed in some other colon cancer cells. In normal tissues, KRAP was strongly expressed in pancreas and testis. Anti-KRAP polyclonal antibodies detected endogenous KRAP as the molecular size of Mr 180,000, and immunofluorescence microscopy and cytochalasin E treatment revealed that KRAP was clearly associated with the actin filaments. Furthermore, KRAP was localized as a membrane-bound form with extracellular regions. These results together suggested KRAP might be involved in the regulation of filamentous actin and signals from the outside of the cells.

A novel mechanism of nuclear factor kappaB activation through the binding between inhibitor of nuclear factor-kappaBalpha and the processed NH(2)-terminal region of Mig-6.

Mitogene-inducible gene-6 (Mig-6), an adaptor molecule containing the Cdc42/Rac interaction and binding (CRIB) domain, is rapidly induced by mitogenic and stressful stimuli, and sustained mig-6 expression is observed in chronic pathological conditions. The function of this molecule has remained elusive. We find that mig-6 is constitutively expressed in many human cancer cell lines, and Mig-6 is cleaved into the NH(2)-terminal region containing the CRIB domain and the remainder of the COOH-terminal region by limited proteolytic processing. We report here that full-length Mig-6, but not CRIB domain-deleted Mig-6 (DeltaMig-6) or uncleavable mutant of Mig-6 (Mig-6-S38A), induces transcriptional activation of nuclear factor of kappaB (NFkappaB), which is inhibited by inhibitor of kappaBalpha (IkappaBalpha), and that the processed NH(2)-terminal region of Mig-6 but not the full length is bound with IkappaBalpha through its NFkappaB binding region. These findings suggest that the processed CRIB domain of Mig-6 will compete with NFkappaB for IkappaBalpha and result in NFkappaB activation. This novel NFkappaB activation pathway provides new insights regarding tumorigenesis, and the specific inhibition of the cleavage of Mig-6 may be a target for clinical treatment.