Neutrophil transfer of miR-223 to lung epithelial cells dampens acute lung injury in mice

Intercellular transfer of microRNAs can mediate communication between critical effector cells. We hypothesized that transfer of neutrophil-derived microRNAs to pulmonary epithelial cells could alter mucosal gene expression during acute lung injury. Pulmonary-epithelial microRNA profiling during coculture of alveolar epithelial cells with polymorphonuclear neutrophils (PMNs) revealed a selective increase in lung epithelial cell expression of microRNA-223 (miR-223). Analysis of PMN-derived supernatants showed activation-dependent release of miR-223 and subsequent transfer to alveolar epithelial cells during coculture in vitro or after ventilator-induced acute lung injury in mice. Genetic studies indicated that miR-223 deficiency was associated with severe lung inflammation, whereas pulmonary overexpression of miR-223 in mice resulted in protection during acute lung injury induced by mechanical ventilation or by infection with Staphylococcus aureus Studies of putative miR-223 gene targets implicated repression of poly(adenosine diphosphate-ribose) polymerase-1 (PARP-1) in the miR-223-dependent attenuation of lung inflammation. Together, these findings suggest that intercellular transfer of miR-223 from neutrophils to pulmonary epithelial cells may dampen acute lung injury through repression of PARP-1.

Hypoxia-inducible factor 2-alpha-dependent induction of amphiregulin dampens myocardial ischemia-reperfusion injury

Myocardial ischemia–reperfusion injury (IRI) leads to the stabilization of the transcription factors hypoxia-inducible factor 1-alpha (HIF1-alpha) and hypoxia-inducible factor 2-alpha (HIF2-alpha). While previous studies implicate HIF1-alpha in cardioprotection, the role of HIF2-alpha remains elusive. Here we show that HIF2-alpha induces the epithelial growth factor amphiregulin (AREG) to elicit cardioprotection in myocardial IRI. Comparing mice with inducible deletion of Hif1a or Hif2a in cardiac myocytes, we show that loss of Hif2-alpha increases infarct sizes. Microarray studies in genetic models or cultured human cardiac myocytes implicate HIF2-alpha in the myocardial induction of AREG. Likewise, AREG increases in myocardial tissues from patients with ischemic heart disease. Areg deficiency increases myocardial IRI, as does pharmacologic inhibition of Areg signaling. In contrast, treatment with recombinant Areg provides cardioprotection and reconstitutes mice with Hif2a deletion. These studies indicate that HIF2-alpha induces myocardial AREG expression in cardiac myocytes, which increases myocardial ischemia tolerance.

Myocardial ischemia–reperfusion injury stabilizes the hypoxia-inducible factor HIF2-alpha. Here, the authors show that HIF2-alpha protects the heart from injury via induction of the epidermal growth factor amphiregulin, and that amphiregulin administration is cardioprotective in mice.

A model-specific role of microRNA-223 as a mediator of kidney injury during experimental sepsis

Sepsis outcomes are heavily dependent on the development of septic organ injury, but no interventions exist to interrupt or reverse this process. microRNA-223 (miR-223) is known to be involved in both inflammatory gene regulation and host-pathogen interactions key to the pathogenesis of sepsis. The goal of this study was to determine the role of miR-223 as a mediator of septic kidney injury. Using miR-223 knockout mice and multiple models of experimental sepsis, we found that miR-223 differentially influences acute kidney injury (AKI) based on the model used. In the absence of miR-223, mice demonstrated exaggerated AKI in sterile models of sepsis (LPS injection) and attenuated AKI in a live-infection model of sepsis (cecal ligation and puncture). We demonstrated that miR-223 expression is induced in kidney homogenate after cecal ligation and puncture, but not after LPS or fecal slurry injection. We investigated additional potential mechanistic explanations including differences in peritoneal bacterial clearance and host stool virulence. Our findings highlight the complex role of miR-223 in the pathogenesis of septic kidney injury, as well as the importance of differences in experimental sepsis models and their consequent translational applicability.

Myeloid-derived miR-223 regulates intestinal inflammation via repression of the NLRP3 inflammasome

Neudecker et al. define a role for a microRNA, miR-223, in regulating the inflammatory tone of the intestine by constraining nlrp3 inflammasome activation in CCR2⁺ monocytes and attenuating excessive IL-1β–driven inflammation. Therapeutic nanoparticle delivery of miR-223 mimetics limits experimental colitis.

MicroRNA (miRNA)-mediated RNA interference regulates many immune processes, but how miRNA circuits orchestrate aberrant intestinal inflammation during inflammatory bowel disease (IBD) is poorly defined. Here, we report that miR-223 limits intestinal inflammation by constraining the nlrp3 inflammasome. miR-223 was increased in intestinal biopsies from patients with active IBD and in preclinical models of intestinal inflammation. miR-223^-/y mice presented with exacerbated myeloid-driven experimental colitis with heightened clinical, histopathological, and cytokine readouts. Mechanistically, enhanced NLRP3 inflammasome expression with elevated IL-1β was a predominant feature during the initiation of colitis with miR-223 deficiency. Depletion of CCR2⁺ inflammatory monocytes and pharmacologic blockade of IL-1β or NLRP3 abrogated this phenotype. Generation of a novel mouse line, with deletion of the miR-223 binding site in the NLRP3 3′ untranslated region, phenocopied the characteristics of miR-223^-/y mice. Finally, nanoparticle-mediated overexpression of miR-223 attenuated experimental colitis, NLRP3 levels, and IL-1β release. Collectively, our data reveal a previously unappreciated role for miR-223 in regulating the innate immune response during intestinal inflammation.

NK cells regulate CXCR2+ neutrophil recruitment during acute lung injury

A critical step in the pathogenesis of acute lung injury (ALI) is excessive recruitment of polymorphonuclear neutrophils (PMNs) into the lungs, causing significant collateral tissue damage. Defining the molecular and cellular steps that control neutrophil infiltration and activation during ALI is therefore of important therapeutic relevance. Based on previous findings implicating the transcription factor Tbet in mucosal Th1-inflammation, we hypothesized a detrimental role for Tbet during ALI. In line with our hypothesis, initial studies of endotoxin-induced lung injury revealed a marked protection of Tbet^-/- mice, including attenuated neutrophilia compared to WT counterparts. Surprisingly, subsequent studies identified natural killer (NK) cells as the major source of pulmonary Tbet during ALI. In addition, a chemokine screen suggested that mature Tbet⁺ NK-cells are critical for the production of pulmonary CXCL1 and -2, thereby contributing to pulmonary PMN recruitment. Indeed, both NK-cell Ab depletion and adoptive transfer studies provide evidence for NK cells in the orchestration of neutrophil recruitment during endotoxin-induced ALI. Taken together, these findings identify a novel role for Tbet⁺ NK-cells in initiating the early events of noninfectious pulmonary inflammation.

Tissue-Resident NK Cells Mediate Ischemic Kidney Injury and Are Not Depleted by Anti-Asialo-GM1 Antibody

NK cells are innate lymphoid cells important for immune surveillance, identifying and responding to stress, infection, and/or transformation. Whereas conventional NK (cNK) cells circulate systemically, many NK cells reside in tissues where they appear to be poised to locally regulate tissue function. In the present study, we tested the contribution of tissue-resident NK (trNK) cells to tissue homeostasis by studying ischemic injury in the mouse kidney. Parabiosis experiments demonstrate that the kidney contains a significant fraction of trNK cells under homeostatic conditions. Kidney trNK cells developed independent of NFIL3 and T-bet, and they expressed a distinct cell surface phenotype as compared with cNK cells. Among these, trNK cells had reduced asialo-GM1 (AsGM1) expression relative to cNK cells, a phenotype observed in trNK cells across multiple organs and mouse strains. Strikingly, anti-AsGM1 Ab treatment, commonly used as an NK cell-depleting regimen, resulted in a robust and selective depletion of cNKs, leaving trNKs largely intact. Using this differential depletion, we tested the relative contribution of cNK and trNK cells in ischemic kidney injury. Whereas anti-NK1.1 Ab effectively depleted both trNK and cNK cells and protected against ischemic/reperfusion injury, anti-AsGM1 Ab preferentially depleted cNK cells and failed to protect against injury. These data demonstrate unanticipated specificity of anti-AsGM1 Ab depletion on NK cell subsets and reveal a new approach to study the contributions of cNK and trNK cells in vivo. In total, these data demonstrate that trNK cells play a key role in modulating local responses to ischemic tissue injury in the kidney and potentially other organs.

Alveolar Epithelial A2B Adenosine Receptors in Pulmonary Protection during Acute Lung Injury

Acute lung injury (ALI) is an acute inflammatory lung disease that causes morbidity and mortality in critically ill patients. However, there are many instances where ALI resolves spontaneously through endogenous pathways that help to control excessive lung inflammation. Previous studies have implicated the extracellular signaling molecule adenosine and signaling events through the A2B adenosine receptor in lung protection. In this context, we hypothesized that tissue-specific expression of the A2B adenosine receptor is responsible for the previously described attenuation of ALI. To address this hypothesis, we exposed mice with tissue-specific deletion of Adora2b to ALI, utilizing a two-hit model where intratracheal LPS treatment is followed by injurious mechanical ventilation. Interestingly, a head-to-head comparison of mice with deletion of Adora2b in the myeloid lineage (Adora2b(loxP/loxP) LysM Cre(+)), endothelial cells (Adora2b(loxP/loxP) VE-cadherin Cre(+)), or alveolar epithelial cells (Adora2b(loxP/loxP) SPC Cre(+)) revealed a selective increase in disease susceptibility in Adora2b(loxP/loxP) SPC Cre(+) mice. More detailed analysis of Adora2b(loxP/loxP) SPC Cre(+) mice confirmed elevated lung inflammation and attenuated alveolar fluid clearance. To directly deliver an A2B adenosine receptor-specific agonist to alveolar epithelial cells, we subsequently performed studies with inhaled BAY 60-6583. Indeed, aerosolized BAY 60-6583 treatment was associated with attenuated pulmonary edema, improved histologic lung injury, and dampened lung inflammation. Collectively, these findings suggest that alveolar epithelial A2B adenosine receptor signaling contributes to lung protection, and they implicate inhaled A2B adenosine receptor agonists in ALI treatment.

Mammalian Ste20-like kinase 4 promotes pituitary cell proliferation and survival under hypoxia

The genetic and molecular mechanisms that initiate and maintain pituitary tumorigenesis are poorly understood. Nonfunctioning tumors of the gonadotrope lineage represent 35% of all tumors; are usually macroadenomas, often resulting in hypopituitarism; and have no medical treatments. Using expression microarrays combined with whole-genome copy number screens on individual human tumors, we identified the mammalian sterile-20-like kinase (MST4) transcript, which was amplified within chromosome Xq26.2 in one tumor and up-regulated in all gonadotrope tumor samples. MST4 mRNA and protein were consistently overexpressed in human tumors compared with normal pituitaries. To mimic the pituitary tumor microenvironment, a hypoxia model using LβT2 murine gonadotrope cells was created to examine the functional role of the kinase. During long-term hypoxia, MST4 expression increased colony formation in a soft agar assay and rates of cell proliferation by activating p38 MAPK and AKT. Under short-term severe hypoxic stress, MST4 decreased the rates of apoptosis via p38 MAPK, AKT, hypoxia-inducible factor-1, and its cell-specific downstream targets. Analysis of MST4 mutants confirmed the importance of the kinase sequence but not the regulatory C terminus for its functional effects. Together these data identify the MST4 kinase as a novel candidate to mediate human pituitary tumorigenesis in a hypoxic environment and position it as a potential therapeutic target.

Identification of hypoxia-inducible factor HIF-1A as transcriptional regulator of the A2B adenosine receptor during acute lung injury

Although acute lung injury (ALI) contributes significantly to critical illness, resolution often occurs spontaneously through endogenous pathways. We recently found that mechanical ventilation increases levels of pulmonary adenosine, a signaling molecule known to attenuate lung inflammation. In this study, we hypothesized a contribution of transcriptionally controlled pathways to pulmonary adenosine receptor (ADOR) signaling during ALI. We gained initial insight from microarray analysis of pulmonary epithelia exposed to conditions of cyclic mechanical stretch, a mimic for ventilation-induced lung disease. Surprisingly, these studies revealed a selective induction of the ADORA2B. Using real-time RT-PCR and Western blotting, we confirmed an up to 9-fold induction of the ADORA2B following cyclic mechanical stretch (A549, Calu-3, or human primary alveolar epithelial cells). Studies using ADORA2B promoter constructs identified a prominent region within the ADORA2B promoter conveying stretch responsiveness. This region of the promoter contained a binding site for the transcription factor hypoxia-inducible factor (HIF)-1. Additional studies using site-directed mutagenesis or transcription factor binding assays demonstrated a functional role for HIF-1 in stretch-induced increases of ADORA2B expression. Moreover, studies of ventilator-induced lung injury revealed induction of the ADORA2B during ALI in vivo that was abolished following HIF inhibition or genetic deletion of Hif1a. Together, these studies implicate HIF in the transcriptional control of pulmonary adenosine signaling during ALI.

CD73+ regulatory T cells contribute to adenosine-mediated resolution of acute lung injury

Acute lung injury (ALI) is characterized by alveolar injury and uncontrolled inflammation. Since most cases of ALI resolve spontaneously, understanding the endogenous mechanisms that promote ALI resolution is important to developing effective therapies. Previous studies have implicated extracellular adenosine signaling in tissue adaptation and wound healing. Therefore, we hypothesized a functional contribution for the endogenous production of adenosine during ALI resolution. As a model, we administered intratracheal LPS and observed peak lung injury at 3 d, with resolution by d 14. Treatment with pegylated adenosine-deaminase to enhance extracellular adenosine breakdown revealed impaired ALI resolution. Similarly, genetic deletion of cd73, the pacemaker for extracellular adenosine generation, was associated with increased mortality (0% wild-type and 40% in cd73(-/-) mice; P<0.05) and failure to resolve ALI adequately. Studies of inflammatory cell trafficking into the lungs during ALI resolution revealed that regulatory T cells (Tregs) express the highest levels of CD73. While Treg numbers in cd73(-/-) mice were similar to controls, cd73-deficient Tregs had attenuated immunosuppressive functions. Moreover, adoptive transfer of cd73-deficient Tregs into Rag(-/-) mice emulated the observed phenotype in cd73(-/-) mice, while transfer of wild-type Tregs was associated with normal ALI resolution. Together, these studies implicate CD73-dependent adenosine generation in Tregs in promoting ALI resolution.

Crosstalk between the equilibrative nucleoside transporter ENT2 and alveolar Adora2b adenosine receptors dampens acute lung injury

The signaling molecule adenosine has been implicated in attenuating acute lung injury (ALI). Adenosine signaling is terminated by its uptake through equilibrative nucleoside transporters (ENTs). We hypothesized that ENT-dependent adenosine uptake could be targeted to enhance adenosine-mediated lung protection. To address this hypothesis, we exposed mice to high-pressure mechanical ventilation to induce ALI. Initial studies demonstrated time-dependent repression of ENT1 and ENT2 transcript and protein levels during ALI. To examine the contention that ENT repression represents an endogenous adaptive response, we performed functional studies with the ENT inhibitor dipyridamole. Dipyridamole treatment (1 mg/kg; EC50=10 μM) was associated with significant increases in ALI survival time (277 vs. 395 min; P<0.05). Subsequent studies in gene-targeted mice for Ent1 or Ent2 revealed a selective phenotype in Ent2(-/-) mice, including attenuated pulmonary edema and improved gas exchange during ALI in conjunction with elevated adenosine levels in the bronchoalveolar fluid. Furthermore, studies in genetic models for adenosine receptors implicated the A2B adenosine receptor (Adora2b) in mediating ENT-dependent lung protection. Notably, dipyridamole-dependent attenuation of lung inflammation was abolished in mice with alveolar epithelial Adora2b gene deletion. Our newly identified crosstalk pathway between ENT2 and alveolar epithelial Adora2b in lung protection during ALI opens possibilities for combined therapies targeted to this protein set.

Equilibrative nucleoside transporter 1 (ENT1) regulates postischemic blood flow during acute kidney injury in mice

A complex biologic network regulates kidney perfusion under physiologic conditions. This system is profoundly perturbed following renal ischemia, a leading cause of acute kidney injury (AKI) - a life-threatening condition that frequently complicates the care of hospitalized patients. Therapeutic approaches to prevent and treat AKI are extremely limited. Better understanding of the molecular pathways promoting postischemic reflow could provide new candidate targets for AKI therapeutics. Due to its role in adapting tissues to hypoxia, we hypothesized that extracellular adenosine has a regulatory function in the postischemic control of renal perfusion. Consistent with the notion that equilibrative nucleoside transporters (ENTs) terminate adenosine signaling, we observed that pharmacologic ENT inhibition in mice elevated renal adenosine levels and dampened AKI. Deletion of the ENTs resulted in selective protection in Ent1-/- mice. Comprehensive examination of adenosine receptor-knockout mice exposed to AKI demonstrated that renal protection by ENT inhibitors involves the A2B adenosine receptor. Indeed, crosstalk between renal Ent1 and Adora2b expressed on vascular endothelia effectively prevented a postischemic no-reflow phenomenon. These studies identify ENT1 and adenosine receptors as key to the process of reestablishing renal perfusion following ischemic AKI. If translatable from mice to humans, these data have important therapeutic implications.

Partial netrin-1 deficiency aggravates acute kidney injury

The netrin family of secreted proteins provides migrational cues in the developing central nervous system. Recently, netrins have also been shown to regulate diverse processes beyond their functions in the brain, incluing the ochrestration of inflammatory events. Particularly netrin-1 has been implicated in dampening hypoxia-induced inflammation. Here, we hypothesized an anti-inflammatory role of endogenous netrin-1 in acute kidney injury (AKI). As homozygous deletion of netrin-1 is lethal, we studied mice with partial netrin-1 deletion (Ntn-1^+/− mice) as a genetic model. In fact, Ntn-1^+/− mice showed attenuated Ntn-1 levels at baseline and following ischemic AKI. Functional studies of AKI induced by 30 min of renal ischemia and reperfusion revealed enhanced kidney dysfunction in Ntn-1^+/− mice as assessed by measurements of glomerular filtration, urine flow rate, urine electrolytes, serum creatinine and creatinine clearance. Consistent with these findings, histological studies indicated a more severe degree kidney injury. Similarly, elevations of renal and systemic inflammatory markers were enhanced in mice with partial netrin-1 deficiency. Finally, treatment of Ntn-1^+/− mice with exogenous netrin-1 restored a normal phenotype during AKI. Taking together, these studies implicate endogenous netrin-1 in attenuating renal inflammation during AKI.

CXCR2 agonists in ADPKD liver cyst fluids promote cell proliferation

Autosomal dominant polycystic kidney disease (ADPKD) is a highly prevalent genetic disease that results in cyst formation in kidney and liver. Cytokines and growth factors secreted by the cyst-lining epithelia are positioned to initiate autocrine/paracrine signaling and promote cyst growth. Comparative analyses of human kidney and liver cyst fluids revealed disparate cytokine/growth factor profiles. CXCR2 agonists, including IL-8, epithelial neutrophil-activating peptide (ENA-78), growth-related oncogene-alpha (GRO-alpha), are potent proliferative agents that were found at high levels in liver but not kidney cyst fluids. Liver cysts are lined by epithelial cells derived from the intrahepatic bile duct (i.e., cholangiocytes). In polarized pkd2(WS25/-) mouse liver cyst epithelial monolayers, CXCR2 agonists were released both apically and basally, indicating that they may act both on the endothelial and epithelial cells within or lining the cyst wall. IL-8 and human liver cyst fluid induced cell proliferation of HMEC-1 cells, a human microvascular endothelial cell line, and Mz-ChA1 cells, a human cholangiocyte cell model. IL-8 expression can be regulated by specific stresses. Hypoxia and mechanical stretch, two likely stressors acting on the liver cyst epithelia, significantly increased IL-8 secretion and promoter activity. AP-1, c/EBP, and NF-kappaB were required but not sufficient to drive the stress-induced increase in IL-8 transcription. An upstream element between -272 and -1,481 bp allowed for the stress-induced increase in IL-8 transcription. These studies support the hypothesis that CXCR2 signaling promotes ADPKD liver cyst growth.

VEGF receptor inhibition blocks liver cyst growth in pkd2(WS25/-) mice

Proliferation of cyst-lining epithelial cells is an integral part of autosomal dominant polycystic kidney disease (ADPKD) cyst growth. Cytokines and growth factors within cyst fluids are positioned to induce cyst growth. Vascular endothelial growth factor (VEGF) is a pleiotropic growth factor present in ADPKD liver cyst fluids (human 1,128 +/- 78, mouse 2,787 +/- 136 pg/ml) and, to a lesser extent, in ADPKD renal cyst fluids (human 294 +/- 41, mouse 191 +/- 90 pg/ml). Western blotting showed that receptors for VEGF (VEGFR1 and VEGFR2) were present in both normal mouse bile ducts and pkd2(WS25/-) liver cyst epithelial cells. Treatment of pkd2(WS25/-) liver cyst epithelial cells with VEGF (50-50,000 pg/ml) or liver cyst fluid induced a proliferative response. The effect on proliferation of liver cyst fluid was inhibited by SU-5416, a potent VEGF receptor inhibitor. Treatment of pkd2(WS25/-) mice between 4 and 8 mo of age with SU-5416 markedly reduced the cyst volume density of the liver (vehicle 9.9 +/- 4.3%, SU-5416 1.8 +/- 0.7% of liver). SU-5416 treatment between 4 and 12 mo of age markedly protected against increases in liver weight [pkd2(+/+) 4.8 +/- 0.2%, pkd2(WS25/-)-vehicle 10.8 +/- 1.9%, pkd2(WS25/-)-SU-5416 4.8 +/- 0.4% body wt]. The capacity of VEGF signaling to induce in vitro proliferation of pkd2(WS25/-) liver cyst epithelial cells and inhibition of in vivo VEGF signaling to retard liver cyst growth in pkd2(WS25/-) mice indicates that the VEGF signaling pathway is a potentially important therapeutic target in the treatment of ADPKD liver cyst disease.

Regulated ion transport in mouse liver cyst epithelial cells

Derived from bile duct epithelia (BDE), secretion by liver cyst-lining epithelia is positioned to drive cyst expansion but the responsible ion flux pathways have not been characterized. Cyst-lining epithelia were isolated and cultured into high resistance monolayers to assess the ion secretory pathways. Electrophysiologic studies showed a marked rate of constitutive transepithelial ion transport, including Cl(-) secretion and Na(+) absorption. Na(+) absorption was amiloride-sensitive, suggesting the activation of epithelial sodium channels (ENaC). Further, both cAMP(i) and extracellular ATP induced robust secretory responses. Western blotting and immunohistologic analysis of liver cyst epithelia demonstrated expression of P2X4, a potent purinergic receptor in normal BDE. Luminometry and bioassaying measured physiologically relevant levels of ATP in a subset of liver cyst fluid samples. Liver cyst epithelia also displayed a significant capacity to degrade extracellular ATP. In conclusion, regulated ion transport pathways are present in liver cyst epithelia and are positioned to direct fluid secretion into the lumen of liver cysts and promote increases in liver cyst expansion and growth.

ESX induces transformation and functional epithelial to mesenchymal transition in MCF-12A mammary epithelial cells

ESX is an epithelial-restricted member of a large family of transcription factors known as the Ets family. ESX expression has been shown to be correlated with Her2/neu proto-oncogene amplification in highly aggressive breast cancers and induced by Her2/neu in breast cell lines, but its role in tumorigenesis is unknown. Previously, we have shown that ESX enhances breast cell survival in colony-formation assays. In order to determine whether ESX can act as a transforming gene, we stably transfected MCF-12A human mammary epithelial cells with the ESX expression vector, pCGN2-HA-ESX. The MCF-12A cell line is immortalized, but nontransformed, and importantly, these cells fail to express endogenous ESX protein. We used pCGN2-HA-Ets-2 and pSVRas expression vectors as positive controls for transformation. Like HA-Ets-2 and V12-Ras, stable expression of ESX induced EGF-independent proliferation, serum-independent MAPK phosphorylation and growth in soft agar. Additionally, stable ESX expression conferred increased cell adhesion, motility and invasion in two-dimensional and transwell filter assays, and an epithelial to mesenchymal morphological transition. In three-dimensional cultures, parental and vector control (pCGN2) cells formed highly organized duct-like structures with evidence of cell polarity, ECM adhesion-dependent proliferation and cell survival, and lack of cellular invasion into surrounding matrix. Remarkably, the ESX stable cells formed solid, disorganized structures, with lack of cell polarity, loss of adhesion junctions and cytokeratin staining and loss of dependence on ECM adhesion for cell proliferation and survival. In addition, ESX cells invaded the surrounding matrix, indicative of a transformed and metastatic phenotype. Taken together, these data show that ESX expression alone confers a transformed and in vitro metastatic phenotype to otherwise normal MCF-12A cells.

Purification and mass spectrometric identification of GA-binding protein (GABP) as the functional pituitary Ets factor binding to the basal transcription element of the prolactin promoter

The Ets-binding site within the basal transcription element (BTE) of the rat prolactin (rPRL) promoter is critical for both basal and growth factor-regulated rPRL gene expression. Here we report the purification and identification of the factor that binds to the BTE. This factor was purified from GH3 pituitary nuclear extracts using ammonium sulfate fractionation, heparin-Sepharose and Mono Q chromatography, and BTE-affinity magnetic beads. We purified two proteins of 57 and 47 kDa and identified the 57-kDa protein by mass spectrometry as the Ets factor GABPalpha. Western blot analysis identified the 47-kDa protein as GABPbeta1. Co-transfection of dominant-negative GABPbeta1 blocks prolactin promoter basal activity by 85-88% in GH3 cells in the presence or absence of FGF-4. Additionally, expression of wild-type GABPalpha/beta1 selectively activates a minimal BTE promoter 24-28-fold in GH3 cells, and this activation is dependent on the Ets-binding site. Finally, small interfering RNA depletion of GABP in GH3 cells results in the loss of prolactin protein. Thus, we have identified GABPalpha/GABPbeta1 as a critical and functionally relevant Ets factor that regulates rPRL promoter activity via the BTE site.

The Pit-1 homeodomain and beta-domain interact with Ets-1 and modulate synergistic activation of the rat prolactin promoter

Pit-1/GHF-1 is a pituitary-specific, POU homeodomain transcription factor required for development of somatotroph, lactotroph, and thyrotroph cell lineages and regulation of the temporal and spatial expression of the growth hormone, prolactin (PRL), and thyrotropin-beta genes. Synergistic interaction of Pit-1 with a member of the Ets family of transcription factors, Ets-1, has been shown to be an important mechanism regulating basal and Ras-induced lactotroph-specific rat (r) PRL promoter activity. Pit-1beta/GHF-2, an alternatively spliced isoform containing a 26-amino acid insert (beta-domain) within its transcription-activation domain, physically interacts with Ets-1 but fails to synergize. By using a series of Pit-1 internal-deletion constructs in a transient transfection protocol to reconstitute rPRL promoter activity in HeLa cells, we have determined that the functional and physical interaction of Pit-1 and Ets-1 is mediated via the POU homeodomain, which is common to both Pit-1 and Pit-1beta. Although the Pit-1 homeodomain is both necessary and sufficient for direct binding to Ets-1 in a DNA-independent manner, an additional interaction surface was mapped to the beta-domain, specific to the Pit-1beta isoform. Thus, the unique transcriptional properties of Pit-1 and Pit-1beta on the rPRL promoter may be due to the formation of functionally distinct complexes of these two Pit-1 isoforms with Ets-1.