全反式维甲酸通过抑制ERK和激活p38 MAPK信号诱导KLF4基因表达

全反式维甲酸（all-trans retinoic acid, ATRA）诱导细胞分化与上调转录因子Krüppel样因子4 (KLF4)表达有关, 但目前对ATRA诱导KLF4表达的分子机制尚不清楚．为了研究ATRA在血管平滑肌细胞（VSMC）中诱导KLF4表达的分子机制,本 研究观察ATRA对视黄酸受体α (retinoic acid receptor α, RARα)和KLF4表达的影响及RARα介导ATRA诱导KLF4表达所依 赖的信号转导途径．实验结果显示,ATRA可显著诱导RARα和KLF4表达,用RARα拮抗剂Ro 41 5253阻断ATRA与受体相互作 用后,ATRA诱导的KLF4表达受到显著抑制．用p38 MAPK、ERK和Akt抑制剂阻断ATRA与RARα相互作用所激活的信号转导途径 后,发现阻断p38 MAPK信号途径显著抑制ATRA诱导的KLF4表达,抑制ERK信号途径使ATRA对KLF4表达的诱导作用明显增强, 抑制Akt信号途径不影响KLF4基因表达．表明RARα介导ATRA对KLF4表达的诱导作用,ATRA通过抑制ERK和激活p38 MAPK信号 途径发挥其对KLF4基因表达的诱导作用．     

HIF1α-induced upregulation of KLF4 promotes migration of human vascular smooth muscle cells under hypoxia

Hypoxia-induced vascular smooth muscle cells (VSMCs) migration plays an important role in vascular remodeling and is implicated in vascular diseases, such as atherosclerosis and pulmonary hypertension. We previously observed the increased expression of krüppel-like factor 4 (KLF4) in VSMCs under hypoxia. However, whether the upregulation of KLF4 participates in hypoxia-induced VSMCs migration is still unknown. In this study, we demonstrated that KLF4 was an important player in the process of VSMCs migration under hypoxia since interference of KLF4 by small interfering RNA mostly dampened hypoxia-induced migration of VSMCs. In addition, using luciferase reporter and ChIP assays, we confirmed two hypoxia-inducible factor 1α (HIF1α) binding elements (located at -150 to -163 and -3922 to -3932) in the upstream regulatory region of klf4 locus and identified KLF4 as a novel direct target gene of HIF1α. Our findings unveil a novel regulatory mechanism that involves HIF1α-induced upregulation of KLF4, which plays a vital role in VSMCs migration under hypoxia.     

KLF5与c-Jun相互作用促进Ang II诱导的血管平滑肌细胞增殖

KLF5（Krüppel-like factor 5）是KLF家族转录因子中的成员,参与多种与增 殖相关基因的转录调节.通过体外培养大鼠血管平滑肌细胞（vascular smooth muscle cells, VSMC）,以Ang Ⅱ为增殖诱导因素,研究KLF5介导VSMC增殖的机制. 研究发现,Ang Ⅱ可剂量依赖性诱导VSMC增殖,并伴有KLF5和c-Jun蛋白表达水平的 升高.为了证实KLF5参与Ang Ⅱ诱导的细胞增殖过程,用siRNA敲低内源性KLF5的表达后,发现细胞增殖活力受到明显的抑制;交互免疫沉淀和GST pull down分析结果显示,KLF5与c-Jun在体内和体外存在物理学上的相互作用,并且Ang Ⅱ可诱导二者之间的相互缔合.这些结果表明,KLF5通过与c-Jun相互作用进而介导Ang Ⅱ诱导的VSMC 增殖.     

Metformin ameliorates endotoxemia-induced endothelial pro-inflammatory responses via AMPK-dependent mediation of HDAC5 and KLF2

Exaggerated endothelial pro-inflammatory response is a hallmark in the early stage of sepsis and contributes to the subsequent tissue injury and organ failure. The anti-inflammatory effects of AMP-activated protein kinase (AMPK) activator metformin in sepsis has been revealed. However, the underlying mechanisms remain not fully understood. In the present study, the potential roles of histone deacetylase 5 (HDAC5) and kruppel-like factor 2 (KLF2) in the effects of metformin on endothelial pro-inflammatory responses were investigated. The results showed that metformin pretreatment increased the phosphorylation of HDAC5 at serine 498, leading to the upregulation of KLF2, and eliminated lipopolysaccharide (LPS) and tumor necrosis factor ⍺ (TNF⍺)-induced upregulation of vascular cell adhesion molecule 1 (VCAM1). Furthermore, the adhesion of HL60 leukocytes to endothelial monolayer was effectively inhibited by metformin. In addition, the in vivo data confirmed that AMPK activation attenuated local and systemic inflammation in endotoxic mice induced by LPS via mediating phosphorylating HDAC5 and restoring KLF2 expression. Our findings revealed that AMPK activation-mediated HDAC5 phosphorylation and KLF2 restoration is, at least partially, responsible to the anti-inflammatory effects of metformin in endotoxemia-induced endothelial cells, which has important implications for the future development of interfering therapies of sepsis.     

Phosphorylation of c-Cbl and p85 PI3K driven by all-trans retinoic acid and CD38 depends on Lyn kinase activity

The leukocyte antigen CD38 is expressed after all-trans retinoic acid (ATRA) treatment in HL-60 myelogenous leukemia cells and promotes induced myeloid differentiation when overexpressed. We found that Vav1 and SLP-76 associate with CD38 in two cell lines, and that these proteins complex with Lyn, a Src family kinase (SFK) upregulated by ATRA. SFK inhibitors PP2 and dasatinib, which enhance ATRA-induced differentiation, were used to evaluate the involvement of Lyn kinase activity in CD38-driven signaling. Cells treated with ATRA for 48 h followed by one hour of PP2 incubation show SFK/Lyn kinase inhibition. We observed that Lyn inhibition blocked c-Cbl and p85/p55 PI3K phosphorylation driven by the anti-CD38 agonistic mAb IB4 in ATRA-treated HL-60 cells and untreated CD38 + transfectants. In contrast, cells cultured for 48 h following concurrent ATRA and PP2 treatment did not show Lyn inhibition, suggesting ATRA regulates the effects on Lyn. 48 h of co-treatment preserved CD38-stimulated c-Cbl and p85/p55 PI3K phosphorylation indicating Lyn kinase activity is necessary for these events. In contrast another SFK inhibitor (dasatinib) which blocks Lyn activity with ATRA co-treatment prevented ATRA-induced c-Cbl phosphorylation and crippled p85 PI3K phosphorylation, indicating Lyn kinase activity is important for ATRA-propelled events potentially regulated by CD38. We found that loss of Lyn activity coincided with a decrease in Vav1/Lyn/CD38 and SLP-76/Lyn/CD38 interaction, suggesting these molecules form a complex that regulates CD38 signaling. Lyn inhibition also reduced Lyn and CD38 binding to p85 PI3K, indicating CD38 facilitates a complex responsible for PI3K phosphorylation. Therefore, Lyn kinase activity is important for CD38-associated signaling that may drive ATRA-induced differentiation.     

Synthetic retinoid Am80 inhibits interaction of KLF5 with RARα through inducing KLF5 dephosphorylation mediated by the PI3K/Akt signaling in vascular smooth muscle cells

Krüppel-like factor 5 (KLF5) is known to physically interact with retinoic acid receptor-α (RARα). Here, we show that Am80 inhibited the interaction between KLF5 and RARα and this inhibitory effect was accompanied by the dephosphorylation of KLF5 in VSMCs. Treating VSMCs with LY294002, the PI3K/Akt inhibitor, abrogated Am80-induced KLF5 dephosphorylation and reversed Am80-induced suppression of interaction between KLF5 and RARα, whereas treating vascular smooth muscle cells (VSMCs) with SB203580, the p38 kinase inhibitor, attenuated the interaction between KLF5 and RARα. Constitutively active p38 kinase MKK6b infection prevented the KLF5 dephosphorylation induced by Am80. In conclusion, Am80 induces KLF5 dephosphorylation by activating PI3K/Akt signaling, and inhibits KLF5 phosphorylation by blocking p38 signaling, subsequently leading to the suppression of interaction of KLF5 with RARα.

Structured summary

MINT-7013243: Klf5 (uniprotkb:Q66HP1) physically interacts (MI:0218) with RAR alpha (uniprotkb:Q9QWJ1) by anti bait coimmunoprecipitation (MI:0006)     

Phosphorylation of Kruppel-like factor 5 (KLF5/IKLF) at the CBP interaction region enhances its transactivation function

The Kruppel-like factor 5 (KLF5/IKLF) belongs to the Kruppel family of genes which bind GC-rich DNA elements and activate or repress their target genes in a promoter context and/or cellular environment-dependent manner. In the present study, we used the Gal4 fusion assay system to characterize the mechanism of transactivation by KLF5. We demonstrated that the transactivation function of KLF5 was enhanced by CREB-binding protein (CBP) and blocked by wild-type but not mutant E1A. Over expression of CBP reversed the inhibition effect of E1A. With various lengths of KLF5 fusion protein, the transactivation functions were localized to 156 amino acid residues at the N-terminal region and 133 amino acid residues adjacent to the Zn finger motif. We mapped the CBP and KLF5 interaction domain to the N-terminal region of CBP (amino acids 1–232) and the N-terminal region of KLF5 (amino acids 1–238) where one of the activation functions resides. The histone acetyltransferase (HAT) activity of CBP does not play a role in the transactivation function of KLF5 nor does it acetylate KLF5 in vitro. However, phosphorylation is important in KLF5 transactivation activity. Inhibition of protein kinase activity by H7 or calphostin C blocked both full-length and N-terminal fragment (amino acids 1–238) KLF5 activities. Mutation at a potential protein kinase C phosphorylation site within the CBP interaction domain of KLF5 reduces its transactivation function. Furthermore, using the GST pull-down approach, we showed that phosphorylation of KLF5 enhances its interaction with CBP. The results of the present study provide a mechanism for KLF5 transactivation function.