Overexpression Of KLF15 Research Articles

KLF15 alleviates oxidative stress and apoptosis of H/R-induced trophoblast cells to improve invasion and migration capacity via the activation of IGF1R

BackgroundKrüppel-like factor 15 (KLF15) has been reported to be involved in ischemia injury of multiple types of diseases. Nevertheless, the roles and underlying mechanisms of KLF15 in preeclampsia (PE) are still unclear. MethodsIn this study, the expression of KLF15 in placenta tissues and hypoxia/reoxygenation (H/R)-induced HTR8/SVneo cells was evaluated by GSE66273 database, qRT-PCR and western blot assay. CCK-8 assay was employed to detect cell proliferation. Wound healing assay and transwell assay were used to detect cell migration and invasion. Cell oxidative stress was measured by DCFH-DA staining and kits. Cell apoptosis was evaluated by TUNEL assay and western blot assay. The JASPAR database was used to analyze the binding site of KLF15 and insulin-like growth factor-1 receptor (IGF1R) promoter region. The luciferase reporter assay was used to detect IGF1R promoter activity and ChIP assay was used to verify the combination of KLF15 and IGF1R promoter. Moreover, western blot was employed to measure the expressions of PI3K/Akt-related proteins. ResultsThe data showed that the expression of KLF15 was significantly downregulated in GSE66273 database, tissues and HTR8/SVneo cells. KLF15 overexpression increased H/R-induced HTR8/SVneo cell proliferation, invasion and migration, and inhibited oxidative stress and cell apoptosis. In addition, IGF1R was highly expressed in H/R-induced HTR8/SVneo cells after KLF15 overexpression, and the binding of KLF15 and IGF1R promoter was verified. Silencing of IGF1R reversed the effects of KLF15 overexpression on H/R-induced HTR8/SVneo cell proliferation, migration, invasion, oxidative stress and cell apoptosis. Moreover, KLF15 overexpression and IGF1R silencing regulated the expressions of PI3K/Akt-related proteins in H/R-induced HTR8/SVneo cells. ConclusionIn conclusion, KLF15 overexpression promoted the proliferation and metastasis, and suppressed oxidative stress and cell apoptosis of H/R-induced HTR8/SVneo cells through mediating the PI3K/Akt pathway, which may provide a promising target for the treatment of preeclampsia.

Exploring the Mechanism of KLF15 on the Biological Activity and Autophagy of Gastric Cancer Cells based on PI3K/Akt/Mtor Signaling Pathway.

To explore the mechanism of KLF15 on the biological activity and autophagy of gastric cancer cells based on the PI3K/Akt/mTOR signaling pathway. The gastric cancer AGS cells were divided into the Con group, pcDNANC group, pcDNA-KLF15 group, LY294002 group and IGF-1 group. RT-PCR was used to detect the expression of KLF15 in human gastric mucosal cells and gastric cancer cells; MTT method to detect cell proliferation; Transwell method to detect cell invasion; flow cytometry to detect cell apoptosis; Western blotting to detect PI3K, Akt, mTOR in cells, LC3, Beclin1, p62 protein expression.P<0.05 was used to indicate statistical significance. Compared with the human gastric mucosal cell line GES-1 cells, the expression of KLF15 in human gastric cancer cell lines MKN-28, MFC, SCG-7901 and AGS cells was significantly decreased, And the expression of KLF15 in AGS cells, was the lowest (P=0.006). Compared with the Con group, The expression of KLF15 in the cells of the PCDNA-KLF15 group was significantly increased (P=0.018); There was no significant difference in the expression of KLF15 between the Con group and the PCDNA-NC group (P=0.225). Compared with the Con group, the proliferation and invasion abilities of the cells in the pcDNA-KLF15 group were significantly reduced, And the apoptosis ability was significantly increased (P=0.019). The ratio of LC3II/LC31 and the expression of Beclin1 Protein in the control group were significantly higher than those in the Con group (P=0.017). Overexpression of KLF15 can inhibit the proliferation and invasion of Gastric cancer cells and promote cell apoptosis and autophagy, and its mechanism may be related to the regulation of the PI3K/Akt/mTOR signaling pathway.

Krüppel-like factor 15 counteracts endoplasmic reticulum stress and suppresses lung fibroblast proliferation and extracellular matrix accumulation

The incidence of pulmonary fibrosis is on the rise, and existing treatments have limited efficacy in improving patient survival. The purpose of this study was to reveal the potential of Krüppel-like factor (KLF)15 activation in alleviating pulmonary fibrosis. Transforming growth factor beta (TGF-β) was utilized to induce lung fibroblasts to establish an in vitro model of pulmonary fibrosis. The impacts of TGF-β and KLF15 level on cell proliferation, migration, extracellular matrix (ECM) accumulation, and endoplasmic reticulum stress (ERS) were assessed. Additionally, tunicamycin, an ERS agonist, was used to investigate the role of ERS in KLF15 regulation. The results showed that KLF15 was dropped in response to TGF-β treatment. However, KLF15 overexpression reduced cell proliferation, migration, ECM accumulation, and ERS, alleviating the effects of TGF-β stimulation. Subsequent treatment with tunicamycin diminished the effects of KLF15 overexpression, demonstrating that ERS mediated the modulation of KLF15. KLF15 acts against ERS and suppresses excessive proliferation and ECM accumulation in lung fibroblast. These findings suggest that activating KLF15 is a promising strategy for alleviating pulmonary fibrosis.

Systematic discovery of transcription factors that improve hPSC-derived cardiomyocyte maturation via temporal analysis of bioengineered cardiac tissues.

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have the potential to become powerful tools for disease modeling, drug testing, and transplantation; however, their immaturity limits their applications. Transcription factor (TF) overexpression can improve hPSC-CM maturity, but identifying these TFs has been elusive. Toward this, we establish here an experimental framework for systematic identification of maturation enhancing factors. Specifically, we performed temporal transcriptome RNAseq analyses of progressively matured hPSC-derived cardiomyocytes across 2D and 3D differentiation systems and further compared these bioengineered tissues to native fetal and adult-derived tissues. These analyses revealed 22 TFs whose expression did not increase in 2D differentiation systems but progressively increased in 3D culture systems and adult mature cell types. Individually overexpressing each of these TFs in immature hPSC-CMs identified five TFs (KLF15, ZBTB20, ESRRA, HOPX, and CAMTA2) as regulators of calcium handling, metabolic function, and hypertrophy. Notably, the combinatorial overexpression of KLF15, ESRRA, and HOPX improved all three maturation parameters simultaneously. Taken together, we introduce a new TF cocktail that can be used in solo or in conjunction with other strategies to improve hPSC-CM maturation and anticipate that our generalizable methodology can also be implemented to identify maturation-associated TFs for other stem cell progenies.

The functions and prognostic value of Kr\xfcppel\u2010like factors in breast cancer

BackgroundKrüppel‐like factors (KLFs) are zinc finger proteins which participate in transcriptional gene regulation. Although increasing evidence indicate that KLFs are involved in carcinogenesis and progression, its clinical significance and biological function in breast cancer are still limited.MethodsWe investigated all the expression of KLFs (KLF1-18) at transcriptional levels by using Oncomine and Gene Expression Profiling Interactive Analysis (GEPIA). The mRNA and protein expression levels of KLFs were also determined by using RT-qPCR and immunohistochemistry, respectively. CBioPortal, GeneMANIA and STRING were used to comprehensive analysis of the molecular characteristics of KLFs. The clinical value of prognostic prediction based on the expression of KLFs was determined by using the KM plotter. The relevant molecular pathways of KLFs were further analyzed by using Gene Set Enrichment Analysis (GSEA) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway database. Finally, we investigated the effect of KLF2 and KLF15 on biological behavior of breast cancer cells in vitro.ResultsThe expression of KLF2/4/6/8/9/11/15 was significantly down-regulated in breast cancer. The patients with high KLF2, KLF4 or KLF15 expression had a better outcome, while patients with high KLF8 or KLF11 had a poor prognosis. Furthermore, our results showed that KLF2 or KLF15 can be used as a prognostic factor independent on the other KLFs in patients with breast cancer. Overexpression of KLF2 or KLF15 inhibited cell proliferation and migration, and blocked cell cycle at G0/G1 phase, resulting in cell apoptosis.ConclusionsKLF2 and KLF15 function as tumor suppressors in breast cancer and are potential biomarkers for prognostic prediction in patients with breast cancer.

Depletion of Kruppel-like factor 15 sensitized gliomas to temozolomide cytotoxicity through O6-methylguanine-DNA methyl-transferase

Temozolomide (TMZ)-based chemotherapy is a standard strategy for gliomas, although chemoresistance remains a major therapeutic challenge. The chemical mechanism by which TMZ induces cell death is DNA methylation, leading to double-stranded breaks (DSBs) and thus to apoptosis. However, TMZ-induced N6-meG sites are efficiently repaired and mediated by the DNA repair protein O6-methylguanine-DNA methyl-transferase (MGMT), leading to TMZ resistance. KLF15, a member of the Kruppel-like factors family, mainly functions as transcription factor and potential suppressor gene by inhibiting proliferation, migration, and inducing apoptosis. However, the roles and regulatory mechanisms of KLF15 in glioma tumorigenesis and chemoresistance are poorly understood. In this study, KLF15 expression was upregulated in glioma tissues and cell lines upon TMZ treatment. Knockdown of KLF15 amplified TMZ-induced repression of cell proliferation, while KLF15 overexpression reversed this process. Mechanistically, KLF15 functioned as a transcriptional activator of MGMT. Moreover, KLF15 knockdown sensitized tumors to TMZ treatment in vivo. Taken together, these results suggested that KLF15 up-regulated MGMT through direct binding to the promoter of MGMT, which plays an important role in glioma resistance to TMZ, and which may be a potential target for cancer diagnosis and treatment.

Muscle overexpression of Klf15 via an AAV8-Spc5-12 construct does not provide benefits in spinal muscular atrophy mice

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by loss of the survival motor neuron (SMN) gene. While there are currently two approved gene-based therapies for SMA, availability, high cost, and differences in patient response indicate that alternative treatment options are needed. Optimal therapeutic strategies will likely be a combination of SMN-dependent and -independent treatments aimed at alleviating symptoms in the central nervous system and peripheral muscles. Krüppel-like factor 15 (KLF15) is a transcription factor that regulates key metabolic and ergogenic pathways in muscle. We have recently reported significant downregulation of Klf15 in muscle of presymptomatic SMA mice. Importantly, perinatal upregulation of Klf15 via transgenic and pharmacological methods resulted in improved disease phenotypes in SMA mice, including weight and survival. In the current study, we designed an adeno-associated virus serotype 8 (AAV8) vector to overexpress a codon-optimized Klf15 cDNA under the muscle-specific Spc5-12 promoter (AAV8-Klf15). Administration of AAV8-Klf15 to severe Taiwanese Smn−/−;SMN2 or intermediate Smn2B/− SMA mice significantly increased Klf15 expression in muscle. We also observed significant activity of the AAV8-Klf15 vector in liver and heart. AAV8-mediated Klf15 overexpression moderately improved survival in the Smn2B/− model but not in the Taiwanese mice. An inability to specifically induce Klf15 expression at physiological levels in a time- and tissue-dependent manner may have contributed to this limited efficacy. Thus, our work demonstrates that an AAV8-Spc5-12 vector induces high gene expression as early as P2 in several tissues including muscle, heart, and liver, but highlights the challenges of achieving meaningful vector-mediated transgene expression of Klf15.

Transactivation domain of Krüppel-like factor 15 negatively regulates angiotensin II-induced adventitial inflammation and fibrosis.

Krüppel-like factor (KLF) 15 has emerged as a critical regulator of fibrosis in cardiovascular diseases. However, the precise role that KLF15 and its functional domain played in adventitial inflammation and fibrosis remains unclear. This study aims to investigate the role of the transactivation domain (TAD) of KLF15 in angiotensin II (Ang II)-induced adventitial pathologic changes. KLF15 expression was decreased in the vascular adventitia of Ang II-infused mice (1000 ng/kg/min, 14 d) and in adventitial fibroblasts (AFs) stimulated by Ang II (10-7 M). Adenovirus-mediated KLF15 overexpression normalized Ang II-induced vascular hypertrophy, increased collagen deposition, macrophage infiltration, and CCL2 and VCAM-1 expression. Interestingly, KLF15-ΔTAD (KLF15 with deletion of TAD at amino acids 132-152) overexpression showed no effect on the above pathologic changes. Similarly, perivascularly overexpression of KLF15 but not KLF15-ΔTAD in carotid arteries also attenuated Ang II-induced vascular inflammation and fibrosis. Furthermore, KLF15 overexpression after Ang II infusion rescued Ang II-induced vascular remodeling. CCL2 or VCAM-1-mediated monocyte and macrophage migration or adhesion to AFs in response to Ang II was negatively regulated by KLF15 through TAD. Ang II-enhanced Smad2/3 activation and adventitial migration, proliferation, and differentiation of AFs were suppressed by KLF15 but not KLF15-ΔTAD overexpression. Conversely, small interfering RNA knockdown of KLF15 aggravated Ang II-induced Smad2/3 activation and dysfunction of AFs. Luciferase, coimmunoprecipitation, and chromatin immunoprecipitation assay were used to demonstrate that interaction of KLF15 with Smad2/3 suppressed CCL2 expression through TAD. Mechanistically, activation of Ang II type 1 receptor/phospholipase Cγ 1/ERK1/2 signaling resulted in a decrease of KLF15 expression. In conclusion, these results demonstrate that KLF15 negatively regulates activation of AFs through TAD, which plays an important role in Ang II-induced adventitial inflammation and fibrosis.-Lu, Y.-Y., Li, X.-D., Zhou, H.-D., Shao, S., He, S., Hong, M.-N., Liu, J.-C., Xu, Y.-L., Wu, Y.-J., Zhu, D.-L., Wang, J.-G., Gao, P.-J. Transactivation domain of Krüppel-like factor 15 negatively regulates angiotensin II-induced adventitial inflammation and fibrosis.

Interventions Targeting Glucocorticoid-Krüppel-like Factor 15-Branched-Chain Amino Acid Signaling Improve Disease Phenotypes in Spinal Muscular Atrophy Mice

The circadian glucocorticoid-Krüppel-like factor 15-branched-chain amino acid (GC-KLF15-BCAA) signaling pathway is a key regulatory axis in muscle, whose imbalance has wide-reaching effects on metabolic homeostasis. Spinal muscular atrophy (SMA) is a neuromuscular disorder also characterized by intrinsic muscle pathologies, metabolic abnormalities and disrupted sleep patterns, which can influence or be influenced by circadian regulatory networks that control behavioral and metabolic rhythms. We therefore set out to investigate the contribution of the GC-KLF15-BCAA pathway in SMA pathophysiology of Taiwanese Smn−/−;SMN2 and Smn2B/− mouse models. We thus uncover substantial dysregulation of GC-KLF15-BCAA diurnal rhythmicity in serum, skeletal muscle and metabolic tissues of SMA mice. Importantly, modulating the components of the GC-KLF15-BCAA pathway via pharmacological (prednisolone), genetic (muscle-specific Klf15 overexpression) and dietary (BCAA supplementation) interventions significantly improves disease phenotypes in SMA mice. Our study highlights the GC-KLF15-BCAA pathway as a contributor to SMA pathogenesis and provides several treatment avenues to alleviate peripheral manifestations of the disease. The therapeutic potential of targeting metabolic perturbations by diet and commercially available drugs could have a broader implementation across other neuromuscular and metabolic disorders characterized by altered GC-KLF15-BCAA signaling.

KLF15 regulates in vitro chondrogenic differentiation of human mesenchymal stem cells by targeting SOX9

Mesenchymal stem cells (MSCs) are multipotent stromal cells residing in the bone marrow. MSCs have the potential to differentiate into adipocytes, chondrocytes, and other types of cells. However, the mechanism underlying MSC differentiation is still not fully understood. Here we aimed to investigate the function of the Kruppel-like factor (KLF) transcriptional factor family in regulating chondrogenic differentiation from human MSCs. Among the KLF family members, KLF15 was activated during different models of chondrogenic differentiation in a time-dependent manner. Lentivirus-mediated knockdown of KLF15 in MSCs repressed chondrogenic differentiation whereas KLF15 overexpression facilitated chondrogenic differentiation. KLF15 promoted the chondrogenic differentiation of human MSCs by activating the expression of SOX9, which is critically involved in KLF15 function during chondrogenic differentiation. Our mechanism study demonstrated that KLF15 bound the promoter of SOX9 and promoted the activation of the SOX9 promoter. Taken together, our findings show that KLF15 promotes chondrogenic differentiation of human MSCs by activating SOX9.

KLF15 Inhibits Cell Proliferation in Gastric Cancer Cells via Up-Regulating CDKN1A/p21 and CDKN1C/p57 Expression.

Krüppel-like factors (KLFs) have been identified in multi-cancers and act as oncogenes or tumor suppressors. The function of KLF15, one member of KLFs, has not been well elucidated, especially in gastric cancer (GC). This study was designed to investigate the prognostic value and biological functions of KLF15 in GC. KLF15 protein expression in GC patients was evaluated by immunohistochemistry assays in 50 paired GC tissues and adjacent normal tissues, and correlations between KLF15 expression and clinicopathological characteristics and prognosis were analyzed. Then, we investigated the over-expression of KLF15 on cell proliferation and its mechanism in GC cells. KLF15 expression levels were significantly down-regulated in GC tissues compared to adjacent normal tissues. And KLF15 expression was negatively correlated with clinical stage, lymphatic metastasis, and distant metastasis. Furthermore, KLF15 expression could predict prognosis in patients with GC. Moreover, over-expression of KLF15 could inhibit cell proliferation partly via regulating CDKN1A/p21 and CDKN1C/p57. These findings demonstrate that KLF15 plays a significant role in GC progression and could be a therapeutic target for GC.

KLF15 protects against isoproterenol-induced cardiac hypertrophy via regulation of cell death and inhibition of Akt/mTOR signaling

Increasing evidence indicate that the Krüppel-like factor KLF15, a member of Cys2/His2 zinc-finger DNA-binding proteins, attenuates cardiac hypertrophy. However, the role of KLF15 in cardiovascular system is largely unknown and the exact molecular mechanism of its protective function is not fully elucidated. In the present study, we established a mouse model of cardiac hypertrophy and found that KLF15 expression was down-regulated in hypertrophic hearts. To evaluate the roles of KLF15 in cardiac hypertrophy, we generated transgenic mice overexpressing KLF15 of KLF15 knockdown mice and subsequently induced cardiac hypertrophy. The results indicated that KLF15 overexpression protects mice from ISO-induced cardiac hypertrophy, with reduced ratios of heart weight (HW)/body weight (BW) and cross-sectional area. We also observed that KLF15 overexpression attenuated cardiac fibrosis, inhibited apoptosis and induced autophagy in cardiomyocytes compared with KLF15 knockdown mice. More importantly, we found that the KLF15 overexpression inhibited the Akt/mTOR signaling pathway. Taken together, our findings imply that KLF15 possesses potential anti-hypertrophic and anti-fibrotic functions, possibly via regulation of cell death pathways and the inhibition of Akt/mTOR axis. KLF15 may constitute an efficient candidate drug for the treatment of heart failure and other cardiovascular diseases.

KLF15 Enables Rapid Switching between Lipogenesis and Gluconeogenesis during Fasting

Hepatic lipogenesis is nutritionally regulated (i.e., downregulated during fasting and upregulated during the postprandial state) as an adaptation to the nutritional environment. While alterations in the expression level of the transcription factor SREBP-1c are known to be critical for nutritionally regulatedlipogenesis, upstream mechanisms governing Srebf1 expression remain unclear. Here, we show that the fasting-induced transcription factor KLF15, a key regulator of gluconeogenesis, forms a complex with LXR/RXR, specifically on the Srebf1 promoter. This complex recruits the corepressor RIP140 instead of the coactivator SRC1, resulting in reduced Srebf1 and thus downstream lipogenic enzyme expression during the early and euglycemic period of fasting prior to hypoglycemia and PKA activation. Through this mechanism, KLF15 overexpression specifically ameliorates hypertriglyceridemia without affecting LXR-mediated cholesterol metabolism. These findings reveal a key molecular link between glucose and lipid metabolism and have therapeutic implications for the treatment of hyperlipidemia.

Abstract 344: Kruppel-like Factor 15: A Critical Transcriptional Regulator of Hypoxia Induced Endothelial Arginase 2

Objective: Kruppel Like Factor 15 has recently been shown to be critical for activation of proinflammatory processes in vascular smooth muscle and atherogenesis. Although KLF15 is abundantly expressed in vascular endothelium there is a significant lack of knowledge regarding the role of KLF15 in the regulation of vascular endothelial function. Here we tested the hypothesis that a KLF15 is a critical regulator of Arg2 transcription in response to hypoxia. Approach and Results: Adenoviral mediated augmented expression of KLF15 in human pulmonary microvascular endothelial cells (HPMEC) and in rat pulmonary arteries decreased Arg2 mRNA, protein, and activity. HPMECs exposed to 48 hours of hypoxia exhibited a robust increase in Arg2 protein and mRNA expression and a reciprocal decrease in KLF15 protein levels that remain sustained after 24 hours of reoxygenation. Further, decreased KLF15 protein levels observed in hypoxia exposed HPMEC occurs through augmented conjugation of Ubiquitin to KLF15 that results in enhanced clearance of KLF15 via proteasomal degradation. Chromatin immunoprecipitation indicated direct binding of KLF15 to the Arg2 promoter, which was relieved when HPMEC were exposed to hypoxia, Finally, overexpression of KLF15 reversed hypoxia-induced augmentation of arginase activity and decrements in Nitric Oxide production in HPMEC, and also reversed hypoxia-induced endothelial dysfunction in isolated mice aortic and rat pulmonary artery rings. Conclusions: KLF15 is a critical regulator and repressor of endothelial Arg2 expression, and thereby, NO and pulmonary endothelial function. Overexpression or activation of KLF15 may represent novel therapeutic strategies for pulmonary hypertension.

Transcriptional Regulation of an Insulin-Sensitizing Adipokine Adipolin/CTRP12 in Adipocytes by Krüppel-Like Factor 15

Obese states characterized by chronic inflammation are closely linked to the development of metabolic dysfunction. We identified adipolin/CTRP12 as an insulin-sensitizing and anti-inflammatory adipokine. Although obese conditions down-regulate adipolin expression, its molecular mechanism is largely unknown. Here we show that the transcriptional regulator Krüppel-like factor (KLF) 15 is involved in the regulation of adipolin expression in adipocytes. White adipose tissue from diet-induced obese (DIO) mice showed decreased expression of KLF9 and KLF15 among several KLFs, which was accompanied by reduced expression of adipolin. In cultured 3T3L1 adipocytes, treatment with TNFα significantly reduced the mRNA levels of KLF9, KLF15 and adipolin. Adenovirus-mediated overexpression of KLF15 but not KLF9 reversed TNFα-induced reduction of adipolin expression in adipocytes. Conversely, gene targeting ablation of KLF15 attenuated adipolin expression in adipocytes. Expression of KLF15 but not KLF9 enhanced the promoter activity of adipolin in HEK293 cells. Pretreatment of 3T3L1 adipocytes with the JNK inhibitor SP600125, but not p38 MAPK inhibitor SB203580 blocked the inhibitory effects of TNFα on adipolin and KLF15 expression. These data suggest that adipose inflammation under conditions of obesity suppresses adipolin expression via JNK-dependent down-regulation of KLF15 in adipocytes.

Repression of Cardiac Hypertrophy by KLF15: Underlying Mechanisms and Therapeutic Implications

The Kruppel-like factor (KLF) family of transcription factors regulates diverse cell biological processes including proliferation, differentiation, survival and growth. Previous studies have shown that KLF15 inhibits cardiac hypertrophy by repressing the activity of pivotal cardiac transcription factors such as GATA4, MEF2 and myocardin. We set out this study to characterize the interaction of KLF15 with putative other transcription factors. We first show that KLF15 interacts with myocardin-related transcription factors (MRTFs) and strongly represses the transcriptional activity of MRTF-A and MRTF-B. Second, we identified a region within the C-terminal zinc fingers of KLF15 that contains the nuclear localization signal. Third, we investigated whether overexpression of KLF15 in the heart would have therapeutic potential. Using recombinant adeno-associated viruses (rAAV) we have overexpressed KLF15 specifically in the mouse heart and provide the first evidence that elevation of cardiac KLF15 levels prevents the development of cardiac hypertrophy in a model of Angiotensin II induced hypertrophy.

Expression Profiling Identifies Klf15 as a Glucocorticoid Target That Regulates Airway Hyperresponsiveness

Glucocorticoids (GCs), which activate GC receptor (GR) signaling and thus modulate gene expression, are widely used to treat asthma. GCs exert their therapeutic effects in part through modulating airway smooth muscle (ASM) structure and function. However, the effects of genes that are regulated by GCs on airway function are not fully understood. We therefore used transcription profiling to study the effects of a potent GC, dexamethasone, on human ASM (HASM) gene expression at 4 and 24 hours. After 24 hours of dexamethasone treatment, nearly 7,500 genes had statistically distinguishable changes in expression; quantitative PCR validation of a 40-gene subset of putative GR-regulated genes in 6 HASM cell lines suggested that the early transcriptional targets of GR signaling are similar in independent HASM lines. Gene ontology analysis implicated GR targets in controlling multiple aspects of ASM function. One GR-regulated gene, the transcription factor, Kruppel-like factor 15 (Klf15), was already known to modulate vascular smooth and cardiac muscle function, but had no known role in the lung. We therefore analyzed the pulmonary phenotype of Klf15(-/-) mice after ovalbumin sensitization and challenge. We found diminished airway responses to acetylcholine in ovalbumin-challenged Klf15(-/-) mice without a significant change in the induction of asthmatic inflammation. In cultured cells, overexpression of Klf15 reduced proliferation of HASM cells, whereas apoptosis in Klf15(-/-) murine ASM cells was increased. Together, these results further characterize the GR-regulated gene network in ASM and establish a novel role for the GR target, Klf15, in modulating airway function.

Ligand-based gene expression profiling reveals novel roles of glucocorticoid receptor in cardiac metabolism

Recent studies have documented various roles of adrenal corticosteroid signaling in cardiac physiology and pathophysiology. It is known that glucocorticoids and aldosterone are able to bind glucocorticoid receptor (GR) and mineralocorticoid receptor, and these ligand-receptor interactions are redundant. It, therefore, has been impossible to delineate how these nuclear receptors couple with corticosteroid ligands and differentially regulate gene expression for operation of their distinct functions in the heart. Here, to particularly define the role of GR in cardiac muscle cells, we applied a ligand-based approach involving the GR-specific agonist cortivazol (CVZ) and the GR antagonist RU-486 and performed microarray analysis using rat neonatal cardiomyocytes. We indicated that glucocorticoids appear to be a major determinant of GR-mediated gene expression when compared with aldosterone. Moreover, expression profiles of these genes highlighted numerous roles of glucocorticoids in various aspects of cardiac physiology. At first, we identified that glucocorticoids, via GR, induce mRNA and protein expression of a transcription factor Kruppel-like factor 15 and its downstream target genes, including branched-chain aminotransferase 2, a key enzyme for amino acid catabolism in the muscle. CVZ treatment or overexpression of KLF15 decreased cellular branched-chain amino acid concentrations and introduction of small-interfering RNA against KLF15 cancelled these CVZ actions in cardiomyocytes. Second, glucocorticoid-GR signaling promoted gene expression of the enzymes involved in the prostaglandin biosynthesis, including cyclooxygenase-2 and phospholipase A2 in cardiomyocytes. Together, we may conclude that GR signaling should have distinct roles for maintenance of cardiac function, for example, in amino acid catabolism and prostaglandin biosynthesis in the heart.

The Kru¨ppel-like Factor KLF15 Regulates the Insulin-sensitive Glucose Transporter GLUT4

Resistance to the stimulatory effects of insulin on glucose utilization is a key feature of type 2 diabetes, obesity, and the metabolic syndrome. Recent studies suggest that insulin resistance is primarily caused by a defect in glucose transport. GLUT4 is the main insulin-responsive glucose transporter and is expressed predominantly in muscle and adipose tissues. Whereas GLUT4 has been shown to play a critical role in maintaining systemic glucose homeostasis, the mechanisms regulating its expression are incompletely understood. We have cloned the murine homologue of KLF15, a member of the Krüppel-like family of transcription factors. KLF15 is highly expressed in adipocytes and myocytes in vivo and is induced when 3T3-L1 preadipocytes are differentiated into adipocytes. Overexpression of KLF15 in adipose and muscle cell lines potently induces GLUT4 expression. This effect is specific to KLF15 as overexpression of two other Krüppel-like factors, KLF2/LKLF and KLF4/GKLF, did not induce GLUT4 expression. Both basal (3.3-fold, p < 0.001) and insulin-stimulated (2.4-fold, p < 0.00001) glucose uptake are increased in KLF15-overexpressing adipocytes. In co-transfection assays, KLF15 and MEF2A, a known activator of GLUT4, synergistically activates the GLUT4 promoter. Promoter deletion and mutational analyses provide evidence that this activity requires an intact KLF15-binding site proximal to the MEF2A site. Finally, co-immunoprecipitation assays show that KLF15 specifically interacts with MEF2A. These studies indicate that KLF15 is an important regulator of GLUT4 in both adipose and muscle tissues.