Temporal Control of the TGF-ß Signaling Network by Mouse ESC MicroRNA Targets of Different Affinities.

Although microRNAs (miRNAs) function in the control of embryonic stem cell (ESC) pluripotency, a systems-level understanding is still being developed. Through the analysis of progressive Argonaute (Ago)-miRNA depletion and rescue, including stable Ago knockout mouse ESCs, we uncover transforming growth factor beta (TGF-ß) pathway activation as a direct and early response to ESC miRNA reduction. Mechanistically, we link the derepression of weaker miRNA targets, including TGF-ß receptor 1 (Tgfbr1), to the sensitive TGF-ß pathway activation. In contrast, stronger miRNA targets impart a more robust repression, which dampens concurrent transcriptional activation. We verify such dampened induction for TGF-ß antagonist Lefty. We find that TGF-ß pathway activation contributes to the G1 cell-cycle accumulation of miRNA-deficient ESCs. We propose that miRNA target affinity is a determinant of the temporal response to miRNA changes, which enables the coordination of gene network responses.

Sequestration of microRNA-mediated target repression by the Ago2-associated RNA-binding protein FAM120A.

Argonaute (Ago) proteins interact with various binding partners and play a pivotal role in microRNA (miRNA)-mediated silencing pathways. By utilizing immunoprecipitation followed by mass spectrometry to determine cytoplasmic Ago2 protein complexes in mouse embryonic stem cells (mESCs), we identified a putative RNA-binding protein FAM120A (also known as OSSA/C9ORF10) as an Ago2 interacting protein. Individual nucleotide resolution cross-linking and immunoprecipitation (iCLIP) analysis revealed that FAM120A binds to homopolymeric tracts in 3'-UTRs of about 2000 mRNAs, particularly poly(G) sequences. Comparison of FAM120A iCLIP and Ago2 iCLIP reveals that greater than one-third of mRNAs bound by Ago2 in mESCs are co-bound by FAM120A. Furthermore, such FAM120A-bound Ago2 target genes are not subject to Ago2-mediated target degradation. Reporter assays suggest that the 3'-UTRs of several FAM120A-bound miRNA target genes are less sensitive to Ago2-mediated target repression than those of FAM120A-unbound miRNA targets and FAM120A modulates them via its G-rich target sites. These findings suggest that Ago2 may exist in multiple protein complexes with varying degrees of functionality.

Perianal pyoderma gangrenosum after excision and fulguration of anal condyloma acuminatum.

INTRODUCTION: Pyoderma gangrenosum (PG) is a rare, inflammatory skin pathology frequently associated with systemic inflammatory disease. While rare after surgery, recognition of this disease in the post-surgical setting is important as it can mimic wound infection. PRESENTATION OF CASE: We herein present a dramatic presentation of perianal PG four days after routine excision and fulguration of anal condyloma acuminatum. The affected area did not improve with broad spectrum antibiotics or surgical debridement. A diagnosis of PG was made from clinical suspicion and pathology findings, and further confirmed with rapid improvement after starting steroids. Diagnosis of this disease in the postoperative period requires high suspicion when the characteristic ulcerative or bullae lesions are seen diffusely and show minimal improvement with antibiotic treatment or debridement. DISCUSSION: Our case highlights the importance of recognizing this disease in the post-operative period, to allow for early initiation of appropriate treatment and prevent unnecessary surgical debridement of a highly sensitive area. There have been 32 case reports of PG in the colorectal literature, mostly following stoma creation. There is one case report of idiopathic perianal pyoderma gangrenosum with no known prior trauma. To our knowledge there are no previously reported cases of perianal PG after routine elective anorectal surgery. CONCLUSION: This is the first reported case of perianal pyoderma gangrenosum in the post-surgical setting. Increased awareness of pyoderma gangrenosum in the surgical literature will aid in prompt diagnosis and proper medical management of this uncommon postoperative morbidity.

Argonaute-bound small RNAs from promoter-proximal RNA polymerase II.

Argonaute (Ago) proteins mediate posttranscriptional gene repression by binding guide miRNAs to regulate targeted RNAs. To confidently assess Ago-bound small RNAs, we adapted a mouse embryonic stem cell system to express a single epitope-tagged Ago protein family member in an inducible manner. Here, we report the small RNA profile of Ago-deficient cells and show that Ago-dependent stability is a common feature of mammalian miRNAs. Using this criteria and immunopurification, we identified an Ago-dependent class of noncanonical miRNAs derived from protein-coding gene promoters, which we name transcriptional start site miRNAs (TSS-miRNAs). A subset of promoter-proximal RNA polymerase II (RNAPII) complexes produces hairpin RNAs that are processed in a DiGeorge syndrome critical region gene 8 (Dgcr8)/Drosha-independent but Dicer-dependent manner. TSS-miRNA activity is detectable from endogenous levels and following overexpression of mRNA constructs. Finally, we present evidence of differential expression and conservation in humans, suggesting important roles in gene regulation.

A hypoxia-induced positive feedback loop promotes hypoxia-inducible factor 1alpha stability through miR-210 suppression of glycerol-3-phosphate dehydrogenase 1-like.

Oxygen-dependent regulation of the transcription factor HIF-1α relies on a family of prolyl hydroxylases (PHDs) that hydroxylate hypoxia-inducible factor 1α (HIF-1α) protein at two prolines during normal oxygen conditions, resulting in degradation by the proteasome. During low-oxygen conditions, these prolines are no longer hydroxylated and HIF-1α degradation is blocked. Hypoxia-induced miRNA-210 (miR-210) is a direct transcriptional target of HIF-1α, but its complete role and targets during hypoxia are not well understood. Here, we identify the enzyme glycerol-3-phosphate dehydrogenase 1-like (GPD1L) as a novel regulator of HIF-1α stability and a direct target of miR-210. Expression of miR-210 results in stabilization of HIF-1α due to decreased levels of GPD1L resulting in an increase in HIF-1α target genes. Altering GPD1L levels by overexpression or knockdown results in a decrease or increase in HIF-1α stability, respectively. GPD1L-mediated decreases in HIF-1α stability can be reversed by pharmacological inhibition of the proteasome or PHD activity. When rescued from degradation by proteasome inhibition, elevated amounts of GPD1L cause hyperhydroxylation of HIF-1α, suggesting increases in PHD activity. Importantly, expression of GPD1L attenuates the hypoxic response, preventing complete HIF-1α induction. We propose a model in which hypoxia-induced miR-210 represses GPD1L, contributing to suppression of PHD activity, and increases of HIF-1α protein levels.

GCN5-mediated transcriptional control of the metabolic coactivator PGC-1beta through lysine acetylation.

Changes in expression levels of genes encoding for proteins that control metabolic pathways are essential to maintain nutrient and energy homeostasis in individual cells as well as in organisms. An important regulated step in this process is accomplished through covalent chemical modifications of proteins that form complexes with the chromatin of gene promoters. The peroxisome proliferators gamma co-activator 1 (PGC-1) family of transcriptional co-activators comprises important components of a number of these complexes and participates in a large array of glucose and lipid metabolic adaptations. Here, we show that PGC-1beta is acetylated on at least 10 lysine residues distributed along the length of the protein by the acetyl transferase general control of amino-acid synthesis (GCN5) and that this acetylation reaction is reversed by the deacetylase sirtuin 1 (SIRT1). GCN5 strongly interacts with PGC-1beta and represses its transcriptional activity associated with transcription factors such as ERRalpha, NRF-1, and HNF4alpha, however acetylation and transcriptional repression do not occur when a catalytically inactive GCN5 is co-expressed. Transcriptional repression coincides with PGC-1beta redistribution to nuclear foci where it co-localizes with GCN5. Furthermore, knockdown of GCN5 ablates PGC-1beta acetylation and increases transcriptional activity. In primary skeletal muscle cells, PGC-1beta induction of endogenous target genes, including MCAD and GLUT4, is largely repressed by GCN5. Functionally, this translates to a blunted response to PGC-1beta-induced insulin-mediated glucose transport. These results suggest that PGC-1beta acetylation by GCN5 might be an important step in the control of glucose and lipid pathways and its dysregulation could contribute to metabolic diseases.

O-GlcNAc regulates FoxO activation in response to glucose.

FoxO proteins are key transcriptional regulators of nutrient homeostasis and stress response. The transcription factor FoxO1 activates expression of gluconeogenic, including phosphoenolpyruvate carboxykinase and glucose-6-phosphatase, and also activates the expression of the oxidative stress response enzymes catalase and manganese superoxide dismutase. Hormonal and stress-dependent regulation of FoxO1 via acetylation, ubiquitination, and phosphorylation, are well established, but FoxOs have not been studied in the context of the glucose-derived O-linked beta-N-acetylglucosamine (O-GlcNAc) modification. Here we show that O-GlcNAc on hepatic FoxO1 is increased in diabetes. Furthermore, O-GlcNAc regulates FoxO1 activation in response to glucose, resulting in the paradoxically increased expression of gluconeogenic genes while concomitantly inducing expression of genes encoding enzymes that detoxify reactive oxygen species. GlcNAcylation of FoxO provides a new mechanism for direct nutrient control of transcription to regulate metabolism and stress response through control of FoxO1 activity.

Heterotrophic Archaea dominate sedimentary subsurface ecosystems off Peru.

Studies of deeply buried, sedimentary microbial communities and associated biogeochemical processes during Ocean Drilling Program Leg 201 showed elevated prokaryotic cell numbers in sediment layers where methane is consumed anaerobically at the expense of sulfate. Here, we show that extractable archaeal rRNA, selecting only for active community members in these ecosystems, is dominated by sequences of uncultivated Archaea affiliated with the Marine Benthic Group B and the Miscellaneous Crenarchaeotal Group, whereas known methanotrophic Archaea are not detectable. Carbon flow reconstructions based on stable isotopic compositions of whole archaeal cells, intact archaeal membrane lipids, and other sedimentary carbon pools indicate that these Archaea assimilate sedimentary organic compounds other than methane even though methanotrophy accounts for a major fraction of carbon cycled in these ecosystems. Oxidation of methane by members of Marine Benthic Group B and the Miscellaneous Crenarchaeotal Group without assimilation of methane-carbon provides a plausible explanation. Maintenance energies of these subsurface communities appear to be orders of magnitude lower than minimum values known from laboratory observations, and ecosystem-level carbon budgets suggest that community turnover times are on the order of 100-2,000 years. Our study provides clues about the metabolic functionality of two cosmopolitan groups of uncultured Archaea.