Kun-yong Kim

Adiponectin Is a Negative Regulator of NK Cell Cytotoxicity

NK cells are a key component of innate immune systems, and their activity is regulated by cytokines and hormones. Adiponectin, which is secreted from white adipose tissues, plays important roles in various diseases, including hypertension, cardiovascular diseases, inflammatory disorders, and cancer. In this study the effect of adiponectin on NK cell activity was investigated. Adiponectin was found to suppress the IL-2-enhanced cytotoxic activity of NK cells without affecting basal NK cell cytotoxicity and to inhibit IL-2-induced NF-κB activation via activation of the AMP-activated protein kinase, indicating that it suppresses IL-2-enhanced NK cell cytotoxicity through the AMP-activated protein kinase-mediated inhibition of NF-κB activation. IFN-γ enhances NK cell cytotoxicity by causing an increase in the levels of expression of TRAIL and Fas ligand. The production of IFN-γ, one of the NF-κB target genes in NK cells, was also found to be suppressed by adiponectin, accompanied by the subsequent down-regulation of IFN-γ-inducible TRAIL and Fas ligand expression. These results clearly demonstrate that adiponectin is a potent negative regulator of IL-2-induced NK cell activation and thus may act as an in vivo regulator of anti-inflammatory functions.

Adiponectin-Activated AMPK Stimulates Dephosphorylation of AKT through Protein Phosphatase 2A Activation

Low serum levels of adiponectin are a high risk factor for various types of cancer. Although adiponectin inhibits proliferation and metastasis of breast cancer cells, the underlying molecular mechanisms remain obscure. In this study, we show that adiponectin-activated AMPK reduces the invasiveness of MDA-MB-231 cells by stimulating dephosphorylation of AKT by increasing protein phosphatase 2A (PP2A) activity. Among the various regulatory B56 subunits, B56gamma was directly phosphorylated by AMPK at Ser(298) and Ser(336), leading to an increase of PP2A activity through dephosphorylation of PP2Ac at Tyr(307). We also show that both the blood levels of adiponectin and the tissue levels of PP2A activity were decreased in breast cancer patients and that the direct administration of adiponectin into tumor tissues stimulates PP2A activity. Taken together, these findings show that adiponectin, derived from adipocytes, negatively regulates the invasiveness of breast cancer cells by activating the tumor suppressor PP2A.

Tumor necrosis factor-α and interleukin-1β increases CTRP1 expression in adipose tissue

CTRP1, a member of the CTRP superfamily, consists of an N‐terminal signal peptide sequence followed by a variable region, a collagen repeat domain, and a C‐terminal globular domain. CTRP1 is expressed at high levels in adipose tissues of LPS‐stimulated Sprague‐Dawley rats. The LPS‐induced increase in CTRP1 gene expression was found to be mediated by TNF‐α and IL‐1β. Also, a high level of expression of CTRP1 mRNA was observed in adipose tissues of Zucker diabetic fatty (fa/fa) rats, compared to Sprague‐Dawley rats in the absence of LPS stimulation. These findings indicate that CTRP1 expression may be associated with a low‐grade chronic inflammation status in adipose tissues.

Increase in CIP2A expression is associated with doxorubicin resistance

The cancerous inhibitor of protein phosphatase 2A (CIP2A) increases the migration and metastasis of various cancer cells. Overexpression of CIP2A has been shown to increase the proliferation of MDA‐MB‐231 cells. We thus assessed whether CIP2A expression is associated with sensitivity to doxorubicin. MDA‐MB‐231 cells showed an increase in CIP2A expression after treatment with doxorubicin, while MCF‐7 cells showed a decrease in CIP2A expression. The overexpression of CIP2A in MCF‐7 cells overcame the inhibition of cell proliferation in response to doxorubicin treatment. CIP2A expression was not affected by wild‐type or mutant p53. However, mutant p53 blocked doxorubicin‐mediated CIP2A down‐regulation in HCT116 cells. As a regulation mechanism of doxorubicin‐mediated CIP2A expression, we showed that phosphorylated Akt was involved in the suppression of CIP2A expression.

Adipocyte culture medium stimulates production of macrophage inhibitory cytokine 1 in MDA-MB-231 cells

Obesity is one of the potential risk factors in causing breast cancer. As a result, adipose tissue surrounding breast ductal cells may play an important role in the breast cancer development or progression. To identify the genes that are regulated by factors secreted from adipocytes in breast cancer cells, MDA-MB-231 cells were treated with the culture medium of adipocytes. Most of induced genes were related to immune function and wound healing, which share a common gene expression signature with cancer progression. In present study macrophage inhibitory cytokine 1 (MIC-1) gene was studied among the induced genes. It was found that both MIC-1 mRNA and protein were dramatically increased by the culture medium of adipocytes. Furthermore, proteinase K-treated adipocyte culture supernatants also induced MIC-1 expression. These findings indicate that proteins are not major MIC-1 inducing factors in adipocyte culture medium. Consequently, we examined the effect of free fatty acids such as palmitate and oleate on MIC-1 induction and found that palmitate markedly induced MIC-1 gene expression, whereas oleate did not. Adipocyte culture medium- and palmitate-induced MIC-1 gene expression was mediated by the activation of p38 MAPK, but not by the activation of JNK, ERK, and NF-kappaB pathway. In addition, adipocyte-CM-induced MIC-1 also increased invasiveness of MDA-MB-231 cells.

Dexamethasone reverses TGF-β-mediated inhibition of primary rat preadipocyte differentiation

Dexamethasone and transforming growth factor‐β (TGF‐β) show contrary effects on differentiation of adipocytes. Dexamethasone stimulates adipocyte differentiation whereas TGF‐β inhibits it. In the present study, we investigated whether dexamethasone could reverse the TGF‐β‐mediated inhibition of preadipocyte differentiation. Primary rat preadipocytes, obtained from Sprague–Dawley rats, were pretreated with dexamethasone in the presence or absence of TGF‐β, prior to the induction of differentiation. Co‐treatment of dexamethasone and TGF‐β before inducing differentiation reversed the TGF‐β‐mediated inhibition of preadipocyte differentiation. In order to elucidate the mechanism by which dexamethasone reversed the effect of TGF‐β on the inhibition of preadipocyte differentiation, the expression of CCAAT/enhancer binding protein‐α (C/EBPα) and peroxisome proliferator‐activated receptor γ (PPARγ) was examined. Dexamethasone increased C/EBPα and PPARγ expression in the absence of TGF‐β and also recovered the TGF‐β‐mediated suppression of C/EBPα expression in preadipocytes. Its effect was sustained in differentiated adipocytes as well. However, those effects were not observed in 3T3‐L1 preadipocytes or differentiated adipocytes. These results indicate that dexamethasone reverses the TGF‐β‐mediated suppression of adipocyte differentiation by regulating the expression of C/EBPα and PPARγ, which is dependent on the cellular context.

IFITM6 expression is increased in macrophages of tumor-bearing mice

The family of interferon-induced transmembrane protein (IFITM) genes consists of IFITM1, 2, 3, 5, and 6. They encode cell surface proteins that modulate cell-cell adhesion and cell differentiation. In a previous study, we showed that IFITM1 is involved in the immune escape and metastasis of gastric cancer cells. In this study, we determined the difference in expression of IFITM family genes in tumor-bearing mice. IFITM1 and 6 were found to be significantly increased. IFITM6 gene expression was increased only in the spleen of tumor-bearing mice but not in the bone marrow, lymph node, or thymus. IFITM6 expression was induced in various macrophages, including splenic, thioglycollate-elicited, and bone marrow-derived macrophages, but not in T cells. Lipopolysaccharides (LPS) also increased IFITM6 expression 24 h after administration, and Toll-like receptor 1, 2, 3, 4, and 9 agonists stimulated IFITM6 expression. These findings imply that the increase in IFITM6 expression may be involved in macrophage functions of tumor-bearing mice.

Interleukin-12 p40 gene expression is induced in lipopolysaccharide-activated pituitary glands in vivo.

Proinflammatory cytokines have several functions including activation of the hypothalamo-pituitary-adrenal (HPA) axis and regulation of the immune system. The present study focuses on the regulation of interleukin 12 (IL-12) and its receptor gene expression in the HPA axis under artificially induced immune stress, brought on by administration of lipopolysaccharide (LPS) to Sprague-Dawley (SD) rats. RT-PCR analyses showed that expression of the IL-12 p40 gene was significantly increased and peaked at 2 h in the pituitary gland, but not in the hypothalamus. LPS-induced IL-12 p40 gene induction in the pituitary gland was suppressed after β-adrenoceptor agonist pretreatment in vivo. Both IL-12 p40 gene induction and IL-12 production were also observed when freshly isolated pituitary glands from non-treated SD rats were incubated with LPS in vitro. Furthermore, CD14, which is known as a LPS receptor, was found to be expressed in the pituitary gland. Gel mobility shift assays using nuclear extracts prepared from the pituitary glands of rats administered LPS showed induction of NF-ĸB and AP-1 DNA-binding activity. These results suggest that LPS stimulates the pituitary gland directly in vivo to increase IL-12 p40 gene expression and IL-12 protein production.