Regulation of MicroRNA Machinery and Development by Interspecies S-Nitrosylation.

Bioactive molecules can pass between microbiota and host to influence host cellular functions. However, general principles of interspecies communication have not been discovered. We show here in C. elegans that nitric oxide derived from resident bacteria promotes widespread S-nitrosylation of the host proteome. We further show that microbiota-dependent S-nitrosylation of C. elegans Argonaute protein (ALG-1)-at a site conserved and S-nitrosylated in mammalian Argonaute 2 (AGO2)-alters its function in controlling gene expression via microRNAs. By selectively eliminating nitric oxide generation by the microbiota or S-nitrosylation in ALG-1, we reveal unforeseen effects on host development. Thus, the microbiota can shape the post-translational landscape of the host proteome to regulate microRNA activity, gene expression, and host development. Our findings suggest a general mechanism by which the microbiota may control host cellular functions, as well as a new role for gasotransmitters.

Krüppel-like factor 15: Regulator of BCAA metabolism and circadian protein rhythmicity.

Regulation of nutrient intake, utilization, and storage exhibits a circadian rhythmicity that allows organisms to anticipate and adequately respond to changes in the environment across day/night cycles. The branched-chain amino acids (BCAAs) leucine, isoleucine, and valine are important modulators of metabolism and metabolic health - for example, their catabolism yields carbon substrates for gluconeogenesis during periods of fasting. Krüppel-like factor 15 (KLF15) has recently emerged as a critical transcriptional regulator of BCAA metabolism, and the absence of this transcription factor contributes to severe pathologies such as Duchenne muscular dystrophy and heart failure. This review highlights KLF15's role as a central regulator of BCAA metabolism during periods of fasting, throughout day/night cycles, and in experimental models of muscle disease.

High-throughput screening for TLR3-IFN regulatory factor 3 signaling pathway modulators identifies several antipsychotic drugs as TLR inhibitors.

TLR3 is one of the major innate immune sensors of dsRNA. The signal transduction pathway activated by TLR3, upon binding to dsRNA, leads to the activation of two major transcription factors: NF-kappaB and IFN regulatory factor (IRF) 3. In an effort to identify specific chemical modulators of TLR3-IRF3 signal transduction pathway, we developed a cell-based readout system. Using the IFN-stimulated gene 56 promoter-driven firefly luciferase gene stably integrated in a TLR3-expressing HEK293 cell line, we were able to generate a cell line where treatment with dsRNA resulted in a dose-dependent induction of luciferase activity. A screen of two pharmacologically active compound libraries using this system identified a number of TLR3-IRF3 signaling pathway modulators. Among them we focused on a subset of inhibitors and characterized their mode of action. Several antipsychotic drugs, such as sertraline, trifluoperazine, and fluphenazine, were found to be direct inhibitors of the innate immune signaling pathway. These inhibitors also showed the ability to inhibit IFN-stimulated gene 56 induction mediated by TLR4 and TLR7/8 pathways. Interestingly, they did not show significant effects on TLR3-, TLR7-, and TLR8-mediated NF-kappaB activation. Detailed analysis of the signaling pathway indicated that these drugs might be exerting their inhibitory effects on IRF3 via PI3K signaling pathway. The data presented in this study provide mechanistic explanation of possible anti-inflammatory roles of some antipsychotic drugs.

The Krüppel-Like Factors and Control of Energy Homeostasis.

Nutrient handling by higher organisms is a complex process that is regulated at the transcriptional level. Studies over the past 15 years have highlighted the critical importance of a family of transcriptional regulators termed the Krüppel-like factors (KLFs) in metabolism. Within an organ, distinct KLFs direct networks of metabolic gene targets to achieve specialized functions. This regulation is often orchestrated in concert with recruitment of tissue-specific transcriptional regulators, particularly members of the nuclear receptor family. Upon nutrient entry into the intestine, gut, and liver, KLFs control a range of functions from bile synthesis to intestinal stem cell maintenance to effect nutrient acquisition. Subsequently, coordinated KLF activity across multiple organs distributes nutrients to sites of storage or liberates them for use in response to changes in nutrient status. Finally, in energy-consuming organs like cardiac and skeletal muscle, KLFs tune local metabolic programs to precisely match substrate uptake, flux, and use, particularly via mitochondrial function, with energetic demand; this is achieved in part via circulating mediators, including glucocorticoids and insulin. Here, we summarize current understanding of KLFs in regulation of nutrient absorption, interorgan circulation, and tissue-specific use.

Krüppel-Like Factors in Vascular Inflammation: Mechanistic Insights and Therapeutic Potential.

The role of inflammation in vascular disease is well recognized, involving dysregulation of both circulating immune cells as well as the cells of the vessel wall itself. Unrestrained vascular inflammation leads to pathological remodeling that eventually contributes to atherothrombotic disease and its associated sequelae (e.g., myocardial/cerebral infarction, embolism, and critical limb ischemia). Signaling events during vascular inflammation orchestrate widespread transcriptional programs that affect the functions of vascular and circulating inflammatory cells. The Krüppel-like factors (KLFs) are a family of transcription factors central in regulating vascular biology in states of homeostasis and disease. Given their abundance and diversity of function in cells associated with vascular inflammation, understanding the transcriptional networks regulated by KLFs will further our understanding of the pathogenesis underlying several pervasive health concerns (e.g., atherosclerosis, stroke, etc.) and consequently inform the treatment of cardiovascular disease. Within this review, we will discuss the role of KLFs in coordinating protective and deleterious responses during vascular inflammation, while addressing the potential targeting of these critical transcription factors in future therapies.

Kruppel-like factor 15 is required for the cardiac adaptive response to fasting.

Cardiac metabolism is highly adaptive in response to changes in substrate availability, as occur during fasting. This metabolic flexibility is essential to the maintenance of contractile function and is under the control of a group of select transcriptional regulators, notably the nuclear receptor family of factors member PPARα. However, the diversity of physiologic and pathologic states through which the heart must sustain function suggests the possible existence of additional transcriptional regulators that play a role in matching cardiac metabolism to energetic demand. Here we show that cardiac KLF15 is required for the normal cardiac response to fasting. Specifically, we find that cardiac function is impaired upon fasting in systemic and cardiac specific Klf15-null mice. Further, cardiac specific Klf15-null mice display a fasting-dependent accumulation of long chain acylcarnitine species along with a decrease in expression of the carnitine translocase Slc25a20. Treatment with a diet high in short chain fatty acids relieves the KLF15-dependent long chain acylcarnitine accumulation and impaired cardiac function in response to fasting. Our observations establish KLF15 as a critical mediator of the cardiac adaptive response to fasting through its regulation of myocardial lipid utilization.

Aging and the Krüppel-like factors.

The mammalian Krüppel-like factors (KLFs) are a family of zinc-finger containing transcription factors with diverse patterns of expression and a wide array of cellular functions. While their roles in mammalian physiology are well known, there is a growing appreciation for their roles in modulating the fundamental progression of aging. Here we review the current knowledge of Krüppel-like factors with a focus on their roles in processes regulating aging and age-associated diseases.

A conserved KLF-autophagy pathway modulates nematode lifespan and mammalian age-associated vascular dysfunction.

Loss of protein and organelle quality control secondary to reduced autophagy is a hallmark of aging. However, the physiologic and molecular regulation of autophagy in long-lived organisms remains incompletely understood. Here we show that the Kruppel-like family of transcription factors are important regulators of autophagy and healthspan in C. elegans, and also modulate mammalian vascular age-associated phenotypes. Kruppel-like family of transcription factor deficiency attenuates autophagy and lifespan extension across mechanistically distinct longevity nematode models. Conversely, Kruppel-like family of transcription factor overexpression extends nematode lifespan in an autophagy-dependent manner. Furthermore, we show the mammalian vascular factor Kruppel-like family of transcription factor 4 has a conserved role in augmenting autophagy and improving vessel function in aged mice. Kruppel-like family of transcription factor 4 expression also decreases with age in human vascular endothelium. Thus, Kruppel-like family of transcription factors constitute a transcriptional regulatory point for the modulation of autophagy and longevity in C. elegans with conserved effects in the murine vasculature and potential implications for mammalian vascular aging.KLF family transcription factors (KLFs) regulate many cellular processes, including proliferation, survival and stress responses. Here, the authors position KLFs as important regulators of autophagy and lifespan in C. elegans, a role that may extend to the modulation of age-associated vascular phenotypes in mammals.

Defective NF-κB signaling in metastatic head and neck cancer cells leads to enhanced apoptosis by double-stranded RNA.

Ligands to several Toll-like receptors (TLR), which mediate innate immune responses and chronic inflammation have been used as adjuvants to immunotherapy to enhance their antitumor activity. In particular, double-stranded RNAs that are cognate ligands of TLR3 have been used to trigger proapoptotic activity in cancer cells. However, a mechanistic understanding of TLR3-mediated apoptosis and its potential involvement in controlling tumor metastasis has been lacking. In this study, we used paired cell lines and fresh tumor specimens, derived from autologous primary and metastatic head and neck squamous cell carcinoma, to investigate the role of TLR3 signaling in metastatic progression. Compared with primary tumor cells, metastatic tumor cells were highly sensitive to TLR3-mediated apoptosis after double-stranded RNA treatment. Enhanced apoptosis in metastatic cells was dependent on double-stranded RNA and TLR3 and also the TLR3 effector signaling protein TRIF. Downstream responses requiring NF-κB were critical for apoptosis in metastatic cells, the defects in which could be resuscitated by alternative pathways of NF-κB activation. By elucidating how TLR3 ligands trigger apoptosis in metastatic cells, our findings suggest insights into how to improve their clinical use.