Dual inhibition of REV-ERBß and autophagy as a novel pharmacological approach to induce cytotoxicity in cancer cells.

REV-ERBα and REV-ERBß nuclear receptors regulate several physiological processes, including circadian rhythm and metabolism. A previous study reported the REV-ERBα gene to be co-overexpressed with ERBB2 in breast cancer cell lines. Surprisingly, we found that several tumor types, including a number of breast cancer cell lines, predominantly express the REV-ERBß variant. This pattern was independent of ERBB2 and ER status, and opposite to that of non-cancer mammary epithelial HMEC cells, in which REV-ERBα was the major variant. Consistent with this molecular profile, REV-ERB target genes in both circadian and metabolic pathways were derepressed upon silencing of REV-ERBß, but not REV-ERBα. Strikingly, we found that REV-ERBß is a determinant of sensitivity to chloroquine, a clinically relevant lysosomotropic agent that suppresses autophagy. The cytoprotective function of REV-ERBß appears to operate downstream of autophagy blockade. Through compound screening, we identified ARN5187, a novel lysosomotropic REV-ERBß ligand with a dual inhibitory activity toward REV-ERB-mediated transcriptional regulation and autophagy. Remarkably, although ARN5187 and chloroquine share similar lysosomotropic potency and have a similar effect on autophagy inhibition, ARN5187 is significantly more cytotoxic. Collectively, our results reveal that dual inhibition of REV-ERBß and autophagy is an effective strategy for eliciting cytotoxicity in cancer cells. Furthermore, our discovery of a novel inhibitor compound of both REV-ERB and autophagy may provide a scaffold for the discovery of new multifunctional anticancer agents.

Decreased mitogen activated protein kinase activities in congenital diaphragmatic hernia-associated pulmonary hypoplasia.

BACKGROUND/PURPOSE: The mechanisms that cause pulmonary hypoplasia associated with congenital diaphragmatic hernia (CDH) currently are unknown. The authors proposed that the reduced size and immaturity of these lungs may be associated with differences in the levels of mitogen activated protein (MAP) kinase phosphorylation (extracellular signal regulated protein kinases, ERK-1 and -2). METHODS: ERK-1 activities were measured using immune-complex kinase assays on fetal whole-lung lysates obtained from both nitrofen and olive oil-treated (control) pregnant rats. In addition, ERK-1 and ERK-2 functional activities were estimated by semiquantitative Western blot analysis, using an antibody specific for the diphosphorylated (dp-ERK, activated) forms of the enzymes. RESULTS: ERK-1 activities, measured using immune-complex kinase assays, were reduced in CDH lungs compared with olive oil-treated controls (P <.02). In addition, dp-ERK-1 and dp-ERK-2 levels were found to be reduced in CDH lungs compared with controls (dp-ERK-1, P =.003; dp-ERK-2, P =.04), whereas ERK-1 and ERK-2 protein levels were unchanged. CONCLUSIONS: The lower values of ERK-1 activity and reduced amounts of dp-ERK-1 and dp-ERK-2 in lung tissue from CDH animals, suggests that ERK-1 and ERK-2 activities are reduced in pulmonary hypoplasia associated with CDH. The observed reduction in ERK-1 and ERK-2 activities implicates attenuated cell signaling upstream of the ERK-1 and -2 enzymes.

Regulation of the G protein Galphai2 by growth and development in fetal airway epithelium.

Heterotrimeric guanine nucleotide-binding (G) proteins transduce a wide variety of receptor-mediated signals to effectors that are involved in numerous cellular functions, including cell proliferation and differentiation. Thrombin and bombesin/gastrin-releasing peptide mediate their effects via G protein-coupled receptors to regulate lung growth and development. The growth responses of these ligands are likely to be mediated via the Gi subfamily of G proteins, specifically via Galphai2. We hypothesized that Galphai2 is expressed in the lung during ontogeny in a growth-dependent manner, and that Galphai2 regulates cell growth. We demonstrate that Galphai2 is present in the developing lung of Sprague-Dawley rats, and that its expression is enhanced between embryonic Day 19 and postnatal Day 2. The strongest expression occurs in the fetal airway epithelium, and this expression in fetal airway cells is growth-dependent. Galphai2 is localized to the plasma membrane, a location consistent with interaction with growth factor receptors. Inhibition of Gi-family signal transduction by pertussis toxin (10 ng/ml) inhibits DNA synthesis in embryonic Day 19 in fetal airway epithelium. Galphai2 is likely to be a key mediator of growth signals in the developing lung.

The cardiovascular work of competitive dinghy sailing.

BACKGROUND: Hiking is the special manoeuvre, which the dinghy sailor uses to counterbalance the capsizing effect of the wind on the boat. In the present research the work required of the heart by this exercise was studied in the laboratory using a boat simulator. METHODS: Seven Laser male sailors selected from those in the first places in the junior national rank participated in this study. Their endurance, at different levels of isometric hiking efforts, was measured. Energy expenditure due to hiking was estimated from measurements of oxygen consumption, carbon dioxide elimination and blood lactate concentration. The cardiac load was evaluated by measuring blood pressure using the conventional method and heart rate measured by electrocardiography. Cardiac output was measured using the CO2 re-breathing method. Left ventricular work was then calculated as cardiac output multiplied by mean arterial pressure. RESULTS: The most relevant result was that, while whole body cost of hiking was relatively low (about 1 IO2 min-1), the power of the heart was very significant: cardiac output almost doubled with respect to that at rest and arterial mean pressure rose from 12.5 kPa (rest) to 18.5 kPa (hiking). Thus, left ventricular power rose from 1.2 Watt to 3.2 Watt, which is a typical cardiovascular response to muscular isometric contraction. CONCLUSIONS: These results assume relevance when a person's eligibility for sailing sports is evaluated.

G alpha(i-2) mediates renal LLC-PK1 growth by a Raf-independent activation of p42/p44 MAP kinase.

The protooncogene G alpha(i-2) plays a pivotal role in signaling pathways that control renal cell growth and differentiation. Mitogen-activated protein kinases (MAPKs) are potential downstream effectors for G alpha(i-2) in these pathways. In predifferentiated LLC-PK1 renal cells, the temporal maximal expression of G alpha(i-2) coincided with maximal activation of MAPK(p42/p44). By contrast, pertussis toxin treatment of these cells inhibited cell growth and reduced MAPK(p42/p44) activity by 30%. These findings reflected upstream activation of MAPK kinase (MEK1), as transient transfection of cells with a plasmid encoding a constitutively active form of MEK1 increased MAPK(p42/p44) activity and cell growth, whereas treatment with PD-098059, an inhibitor of MEK1 activity, reduced MAPK(p42/p44) activity and cell growth. Expression of a guanosinetriphosphatase (GTPase)-deficient G alpha(i-2) in these cells increased MAPK(p42/p44) activity and correspondingly reduced cell doubling time from 24 to 10 h without altering the activity of Raf-1 or c-Jun/stress-activated protein kinases (SAPKs). By contrast, expression of a GTPase-deficient G alpha(i-3) in these cells reduced both their cell doubling time by 30% and MAPK(p42/p44) activity by 60%. As the known MEKK isoforms (MEKK1, -2, and -3) can also activate SAPKs, these findings suggest the GTP-charged G alpha(i-2) subunit transduces growth signals in renal cells via activation of MAPK(p42/p44) and that such activation may be linked to pathways containing novel MEKK isoforms that preferentially activate MEKs.

Combination of hand and gaze signals during reaching: activity in parietal area 7 m of the monkey.

The role of area 7 m has been studied by recording the activity of single neurons of monkeys trained to fixate and reach toward peripheral targets. The target was randomly selected from eight possible locations on a virtual circle, of radius 30 degrees visual angle from a central target. Three tasks were employed to dissociate hand- from eye-related contributions. In the first task, animals looked and reached to the peripheral target. In a second task, the animal reached to the peripheral target while maintaining fixation on the central target. In the third task, the monkey maintained fixation on peripheral targets that were spatially coincident with those of the reaching tasks. The results show that cell activity in area 7 m relates, for some cells to eye position, for others to hand position and movement, and for the majority of cells to a combination of visuomanual and oculomotor information. This area, therefore, seems to perform an early combination of information in the processing leading from target localization to movement generation.

LLC-PK1 cell growth is repressed by WT1 inhibition of G-protein alpha i-2 protooncogene transcription.

The temporal expression of the early growth response gene (EGR-1) is one molecular mechanism for both maximal activation of the G alpha i-2 gene and accelerated growth in mitotically active predifferentiated LLC-PK1 renal cells. These events are dependent on an enhancer area in the 5'-flanking region of the G alpha i-2 gene that contains an EGR-1 motif (5'-CGCCCCCGC-3'). However, acquisition of the polarized phenotype in LLC-PK1 cells is accompanied by loss of EGR-1 expression and occupancy of the EGR-1 site by nuclear binding proteins other than EGR-1. We now demonstrate that one of these binding proteins is the Wilms' tumor suppressor (WT1). Furthermore, the temporal expression of WT1 in LLC-PK1 cells acquiring the polarized phenotype represses both G alpha i-2 gene activation and growth in these cells. These findings suggest the existence of differentiation-induced pathways in LLC-PK1 cells that alternatively abrogates EGR-1 and promotes WT1 gene expression, thereby modulating a target protooncogene G alpha i-2 that is participatory for growth and differentiation in renal cells. These studies emphasize the usefulness of the LLC-PK1 renal cell as a model to elucidate normal programs of genetic differentiation in which WT1 participates.

Growth of LLC-PK1 renal cells is mediated by EGR-1 up-regulation of G protein alpha i-2 protooncogene transcription.

The early growth response zinc finger transcription factor (EGR-1) and the heterotrimeric guanine nucleotide binding protein encoded by the protooncogene G alpha i-2 each play pivotal roles in signaling pathways that control cell growth and differentiation. The G alpha i-2 gene 5'-flanking region contains a putative binding site (5'-CGCCCCCGC-3') for EGR-1 that may allow it to be a target gene for EGR-1 mitogenic signaling. We now demonstrate in LLC-PK1 renal cells the temporal expression of EGR-1 protein by immunoblotting and immunocytochemistry coincident with the maximal activation of the G alpha i-2 gene during cell growth. To determine whether G alpha i-2 or EGR-1 influence epithelial cell growth, LLC-PK1 cells were transiently transfected with plasmids encoding cDNAs for G alpha i-2 (pRSV G alpha i-2) or EGR-1 (pRSV EGR-1) driven by a viral Rous sarcoma promoter enhancer to overexpress each protein. Following transfection, cell growth was examined in media containing either 10 or 0.1% fetal bovine serum. Only cells transfected with plasmids encoding G alpha i-2 and EGR-1 had growth rates greater than that of serum replete cohorts. To assess whether EGR-1 was contributing to the transcriptional activation of the G alpha i-2 gene, cells were cotransfected with pRSV EGR-1 and plasmids encoding firefly luciferase reporter genes fused to 5'-flanking areas of the G alpha i-2 gene containing either the EGR-1 binding site or a mutated EGR-1 binding site (5'-AAAAACCGC-3'). A 320% enhancement of G alpha i-2 transcription was found only in LLC-PK1 cells following their transfection with plasmids that contained both the EGR-1 binding site and overexpressed EGR-1 protein. Utilizing mobility shift assays, which compared nuclear extracts from cells before and after cell polarization, a probe containing the EGR-1 motif detected induced nuclear protein complexes during transcriptional activation of the G alpha i-2 gene. An anti-EGR-1 antibody specifically retarded the mobility of the induced nuclear complexes, indicating that the EGR-1 protein was a component of these complexes. These data provide direct evidence for a novel mitogenic signaling pathway coupling proximal signaling events that activate EGR-1 gene expression to a target protooncogene G alpha i-2 that is participatory for growth and differentiation in renal cells.

Heterotrimeric G proteins, vesicle trafficking, and CFTR Cl- channels.

Previously (E.M. Schwiebert, N. Kizer, D. C. Gruenert, and B. A. Stanton, Proc. Natl. Acad. Sci. USA 89: 10623-10627, 1992), we showed that heterotrimeric G proteins regulate adenosine 3',5'-cyclic monophosphate (cAMP)-activated cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels in human airway epithelial cells. The goal of the present study was to test the hypothesis that heterotrimeric G proteins regulate vesicle trafficking and exocytosis and that these events are critical for cAMP activation of CFTR-mediated Cl- secretion. We report that cAMP stimulates exocytosis and CFTR Cl- conductance (GCl) in normal but not in CF cells. Stimulation of the heterotrimeric G protein G alpha i-2 inhibited cAMP-activated CFTR GCl and exocytosis in normal cells. In contrast, inhibition of G alpha i-2 stimulated exocytosis and allowed cAMP to stimulate CFTR GCl in cells isolated from patients with cystic fibrosis (CF). Brefeldin A and nocodazol prevented cAMP-induced exocytosis and also blocked cAMP stimulation of CFTR GCl in normal airway epithelial cells. Our studies suggest that the heterotrimeric G protein G alpha i-2 regulates CFTR GCl in human airway epithelial cells by modulating vesicle trafficking and the delivery of CFTR Cl- channels from an intracellular vesicular pool to the plasma membrane. Inhibition of G alpha i-2 may be a useful therapeutic approach to target mutant delta F508 CFTR Cl- channels from an intracellular vesicular pool to the plasma membrane and thereby correct defective Cl- secretion in CF airway epithelial cells.

Isolation and characterization of the promoter of the human GABAA receptor alpha 1 subunit gene.

The GABAA receptor, as assessed by ligand binding and chloride flux measurement in vivo and in vitro, is down-regulated in response to chronic benzodiazepine exposure. The mRNA levels of the alpha 1 and gamma 2 subunits of the receptor are also reduced. We have isolated the promoter of the gene encoding the alpha 1 subunit of the GABAA receptor to elucidate the regulatory mechanism of its expression. A DNA segment 650 bp long has been isolated that includes 151 bp of untranslated 5' end of the cDNA sequence and 500 bp of potential promoter-enhancer region. The transcriptional activity of this DNA segment linked to the firefly luciferase gene showed a strong orientation specificity. The promoter activity was localized to a 60-bp segment by deletion mapping. Mobility shift binding assay results suggest that this segment may interact with one or more factors in HeLa cell nuclear extracts to form a transcriptional complex. Primary cultures of embryonic chick cortical cells transfected with the promoter-luciferase construct were treated chronically with lorazepam. Transcriptional activity of this promoter construct was strongly repressed by chronic administration of lorazepam.

Targeting of chimeric G alpha i proteins to specific membrane domains.

Heterotrimeric guanine nucleotide-regulatory (G) proteins are associated with a variety of intracellular membranes and specific plasma membrane domains. In polarized epithelial LLC-PK1 cells we have shown previously that endogenous G alpha i-2 is localized on the basolateral plasma membrane, whereas G alpha i-3 is localized on Golgi membranes. The targeting of these highly homologous G alpha i proteins to distinct membrane domains was studied by the transfection and expression of chimeric G alpha i proteins in LLC-PK1 cells. Chimeric cDNAs were constructed from the cDNAs for G alpha i-3 and G alpha i-2 and introduced into a pMXX eukaryotic expression vector containing a mouse metallothionein-I promoter. Stably transfected cell lines were produced that expressed either G alpha i-2/3 or G alpha i-3/2 chimeric proteins. Chimeric and endogenous G alpha i proteins were detected in cells using specific carboxy-terminal peptide antibodies. Immunofluorescence staining was used to localize endogenous and chimeric G alpha i proteins in LLC-PK1 cells. The staining of chimeric proteins was detected as an increased intensity of staining on membranes containing endogenous G alpha i proteins. Using confocal microscopy and image analysis we localized G alpha i-2 to a specific sub-domain of the lateral membrane of polarized cells, the chimeric G alpha i-3/2 protein was then shown to colocalize with endogenous G alpha i-2 in the same lateral plasma membrane domain. The chimeric G alpha i-2/3 protein colocalized with endogenous G alpha i-3 on Golgi membranes in LLC-PK1 cells. These results show that chimeric G alpha i proteins were targeted to the same membrane domains as endogenous G alpha i proteins and the specificity of their membrane targeting was conferred by the carboxy-terminal end of the proteins. These data provide the first evidence for specific targeting information contained in the carboxy termini of G alpha i proteins, which appears to be independent of amino-terminal membrane attachment sites in these proteins.

cAMP regulates G-protein alpha i-2 subunit gene transcription in polarized LLC-PK1 cells by induction of a CCAAT box nuclear binding factor.

Heterotrimeric G-proteins function as signal transducers for a variety of hormone-coupled enzyme systems in eukaryotic cells. In LLC-PK1 renal cells, vasopressin-stimulated adenylylcyclase activity is regulated in part, by the counterbalancing activity of stimulatory G-proteins (Gs) and inhibitory pertussis toxin-sensitive G-proteins (Gi). Two Gi genes encoding the Gi isoforms G alpha i-2 and G alpha i-3 are expressed in LLC-PK1 cells. In polarized cells, these isoforms are topographically segregated to different membranes, which allows for the selective inhibition of adenylylcyclase by G alpha i-2. The genes encoding these isoforms are similarly regulated in these cells during growth and differentiation but differ in response to steroid hormone signals (Holtzman, E.J., Kinane, T.B., West, K., Soper, B.W., Karga, H., Ausiello, D.A., and Ercolani, L. (1993) J. Biol. Chem. 268, 3964-3975). We now demonstrate after stimulating polarized LLC-PK1 cells with forskolin, which raises intracellular cAMP levels 50-fold, G alpha i-2 but not G alpha i-3 protein is increased 3-fold at 12 h and remains elevated above control values by 24 h. In cells stably transfected with G alpha i-2 or G alpha i-3 gene 5'-flanking sequences fused to firefly luciferase cDNA reporter gene, forskolin treatment increased G alpha i-2 transcription 3-fold but inhibited G alpha i-3 transcription by 50% at 12 h. In vivo footprinting of forskolin-treated cells was performed to examine the molecular basis for activation of the G alpha i-2 gene. Protected guanosines were identified in a 135-base pair (bp) area previously associated with enhancer activity of this gene in non-polarized cells. This DNA segment did not contain the classical cAMP response element 5'-TGACGTCA-3'. Utilizing the 135-bp DNA segment as a probe in mobility shift assays, which compared nuclear extracts from cells before and after forskolin treatment, an induced nuclear protein complex was identified. Following systematic reduction and mutation of this DNA segment, a "CCAAT" box motif was identified that bound the induced nuclear protein complex during forskolin-induced G alpha i-2 gene transcriptional activation. Induction of this nuclear protein complex was prevented in forskolin-treated cells by cycloheximide. To demonstrate functional activity of the CCAAT box motif, cells were transiently transfected with plasmids encoding either the minimal 135-bp segment or a multimerized CCAAT box segment fused to a Rous sarcoma minimal promoter/firefly luciferase reporter gene.(ABSTRACT TRUNCATED AT 400 WORDS)

Transcriptional regulation of G-protein alpha i subunit genes in LLC-PK1 renal cells and characterization of the porcine G alpha 1-3 gene promoter.

Heterotrimeric guanine nucleotide-binding proteins (G-proteins) function as signal transducers for a variety of hormone-coupled enzyme and ion transport systems in eukaryotic cells. The expression of pertussis toxin-sensitive G-proteins (Gi) which couple their cognate receptors and effectors are regulated by cell cycle-dependent events in porcine LLC-PK1 renal epithelial cells. G alpha i-2 and G alpha i-3 isoforms are detected in these cells, and like G alpha i-2 (Holtzman, E. J., Soper, B. W., Stow, L. L., Ausiello, D. A., and Ercolani, L. (1991) J. Biol. Chem. 266, 1763-1771), we now demonstrate that G alpha i-3 mRNA and protein is coordinately expressed in these cells during differentiation. To gain further insights into these events, the porcine G alpha i-3 gene minimal promoter was characterized and found 67 base pairs upstream from the major transcription start site. The 56-base pair minimal promoter lacked TATAAA and GC boxes but did contain a sequence GGAAGTG conserved in both the human and porcine gene that could potentially bind an adenovirus E4TF1 transcription factor. In cells stably transfected with G alpha i-2 or G alpha i-3 gene 5'-flanking sequences fused to firefly luciferase cDNA reporter, temporal 10-15-fold transcriptional activation of both genes occurred before cellular polarization. Utilizing mobility shift assays which compared nuclear extracts from cells before and after cell polarization, a motif in the 5' region of the gene promoter GTACTTCCGCT was identified that bound an induced nuclear protein complex during transcriptional activation. In polarized cells complemented with the human glucocorticoid receptor, dexamethasone decreased G alpha i-2 but increased G alpha i-3 basal transcription and mRNA content 3-fold. These studies demonstrate that both G alpha i genes are dynamically regulated in LLC-PK1 cells by both growth, differentiation, and hormone signals.

Colocalization of GAPDH and band 3 (AE1) proteins in rat erythrocytes and kidney intercalated cell membranes.

Glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.2.12) (GAPDH) is a multifunctional protein that associates with the cytoplasmic face of intact human erythrocyte membranes. This association has been postulated to be critically dependent on the interaction of GAPDH with the highly acidic NH2-terminal domain of the principal integral membrane protein of the erythrocyte plasma membrane, the band 3 anion exchanger (AE1). This domain is not conserved in murine erythrocyte AE1 and is fully deleted in the alternatively spliced AE1 isoform that is expressed in the kidney. The lack of conservation of this domain has been proposed to explain the reported absence of GAPDH association with rodent erythrocyte membranes. To determine whether GAPDH could be associated with AE1 proteins in rodent cell membranes, specific rabbit antibodies to peptide sequences of rat GAPDH and mouse AE1 were used to immunolocalize these proteins in sequential semithin sections of rat erythrocytes and kidney medulla. In rat erythrocytes, GAPDH immunoreactivity was predominantly membrane associated and colocalized with AE1. In the kidney medulla, GAPDH was concentrated in the basolateral membrane of type A intercalated cells, where it colocalized with the alternatively spliced kidney form of AE1. GAPDH immunoreactivity was not detected in the plasma membrane of any other cell type in the kidney, indicating its predominant association with AE1-rich membranes. If this membrane interaction occurs via AE1 binding, then GAPDH must have binding sites in addition to those previously described for such binding in human AE1.

Identification of a core motif that is recognized by three members of the HMG class of transcriptional regulators: IRE-ABP, SRY, and TCF-1 alpha.

Insulin induces glyceraldehyde-3-phosphate dehydrogenase (GADPH) gene transcription in part by regulating one or more proteins that bind a cis-acting element, IRE-A. We have recently cloned a protein, IRE-ABP, that binds the IRE-A element. IRE-ABP is a member of the HMG class of transcriptional regulators and is 67% identical within its HMG box domain to the candidate gene for the testis-determining factor, SRY. IRE-ABP and SRY share binding specificity for the IRE-A motif. This sequence is also highly conserved with a core motif, 5'-Py-ctttg(a/t)-3', contained in T-cell specific genes that have high affinity for TCF-1 alpha, another member of the HMG class of transcriptional regulators. Thus, diverse members of the HMG family interact with similar nucleotide sequences to regulate expression of genes that initiate and maintain the differentiated phenotype. We have found this core motif in the upstream region of many genes that are positively and negatively regulated by insulin. These observations suggest that IRE-ABP or a related family member may coordinate the expression of these genes. The HMG family of proteins has diverse functions ranging from the regulation of differentiation and mating type in yeast to the regulation of tissue- and species-specific gene expression in mammals. Insulin regulates GAPDH gene transcription in a tissue-specific manner. We propose that members of the IRE-ABP family play an important role in controlling tissue specificity of the insulin response.

Multiple insulin-responsive elements regulate transcription of the GAPDH gene.

Multiple elements in the upstream region of the GAPDH gene play a role in mediating the acute and chronic effect of insulin on GAPDH gene expression. The complexity of this regulation provides many layers of control. In differentiated tissues, the transcriptional response to insulin results from the additive effects of g/TRE, IRE-A and IRE-B. The gTRE may interact with newly synthesized c-fos/c-jun heterodimer to activate GAPDH gene transcription. Studies are underway to determine whether protein synthesis inhibitors affect the regulation of GAPDH. Because there are several elements that mediate the effect, it will be difficult to determine the significance of these findings until each cis-acting factor and its binding protein can be studied in isolation. IRE-A and IRE-B act together to promote a 5- to 8-fold insulin effect on HGAPDH-CAT in H35 hepatoma cells and a 3-fold effect in 3T3 adipocytes. We have succeeded in detecting an insulin-sensitive DNA-binding protein referred to as IREA-BP with an element -480 to -435. Insulin treatment of differentiated 3T3 adipocytes for 1 hr results in a 4-fold increase in the amount of this binding protein, as estimated by the amount of 32P-labelled oligonucleotide retarded on non-denaturing PAGE (11). The effect of insulin on IRP-B is comparable. Furthermore, IREA-BP is induced during the process of fasting and refeeding rats, an important in vivo correlate with our tissue culture models (11). These observations imply that the binding proteins IREA-BP and IRP-B are essential components in the signal transduction pathway of insulin action on GAPDH gene expression in metabolically active tissues such as fat and liver. Differentiation-dependence and tissue-specificity are achieved through multiple regulatory elements and involve pre- and post-translational regulation of multiple transcription factors. IREA-BP is present in preadipocytes but activity in highly induced upon differentiation of preadipocytes to adipocytes. The IRE-B (-408 to -269) DNA binding protein is not detected in 3T3 preadipocytes. A gC/EBP like-protein takes part in the formation of this complex which may explain the inductive effect of differentiation on binding. Finally, footprint and cotransfection studies indicate that the differentiation-dependent protein C/EBP also regulates GAPDH gene transcription through a motif located within one hundred nucleotides of the promoter. We have begun to clone the IRE-A and IRE-B DNA binding proteins. An IRE-A binding protein that footprints the 3' domain of the IRE-A has been cloned.(ABSTRACT TRUNCATED AT 400 WORDS)

A heterotrimeric G protein, G alpha i-3, on Golgi membranes regulates the secretion of a heparan sulfate proteoglycan in LLC-PK1 epithelial cells.

A heterotrimeric G alpha i subunit, alpha i-3, is localized on Golgi membranes in LLC-PK1 and NRK epithelial cells where it colocalizes with mannosidase II by immunofluorescence. The alpha i-3 was found to be localized on the cytoplasmic face of Golgi cisternae and it was distributed across the whole Golgi stack. The alpha i-3 subunit is found on isolated rat liver Golgi membranes by Western blotting and G alpha i-3 on the Golgi apparatus is ADP ribosylated by pertussis toxin. LLC-PK1 cells were stably transfected with G alpha i-3 on an MT-1, inducible promoter in order to overexpress alpha i-3 on Golgi membranes. The intracellular processing and constitutive secretion of the basement membrane heparan sulfate proteoglycan (HSPG) was measured in LLC-PK1 cells. Overexpression of alpha i-3 on Golgi membranes in transfected cells retarded the secretion of HSPG and accumulated precursors in the medial-trans-Golgi. This effect was reversed by treatment of cells with pertussis toxin which results in ADP-ribosylation and functional uncoupling of G alpha i-3 on Golgi membranes. These results provide evidence for a novel role for the pertussis toxin sensitive G alpha i-3 protein in Golgi trafficking of a constitutively secreted protein in epithelial cells.

Regulation of the G-protein alpha i-2 subunit gene in LLC-PK1 renal cells and isolation of porcine genomic clones encoding the gene promoter.

Heterotrimeric G-proteins function as signal transducers for a variety of hormone-coupled enzyme and ion transport systems in eukaryotic cells. We have studied G-protein-coupled processes that appear to be developmentally regulated in polarized pig kidney cells (LLC-PK1). Following trypsinization, LLC-PK1 cells differentiate from a rounded cell type to a fully polarized epithelium by 7 days of culture. During this differentiation, the expression of G-protein alpha i-2 subunit mRNA was not detected until day 4 of culture, it peaked at day 6, and declined thereafter. In contrast, G-protein alpha s subunit mRNA which peaked on day 4 was easily detected on all culture days. The presence of the alpha i-2 protein on epithelial cell basolateral membranes followed the same pattern of mRNA expression during culture. To understand the developmental expression of the alpha i-2 subunit in non-polarized cells and its potential regulation by hormones and second messengers in polarized cells at the transcriptional level, genomic DNA segments encoding the alpha i-2 gene promoter were isolated from an EMBL-3 porcine genomic library. S1 nuclease analysis of LLC-PK1 mRNA with cRNA probes derived from these DNA segments revealed major and a minor transcriptional start sites 131 and 171 base pairs upstream of the translation initiation site. The porcine and human alpha i-2 subunit genes shared a 78% sequence identity in their 5' flanks which suggested an evolutionary conservation of cis elements required to influence their transcription. The porcine alpha i-2 gene promoter was identified by fusing DNA segments encoding putative 5'-flanking areas of the gene to a plasmid that contained a firefly luciferase reporter gene but lacked a promoter. The minimal promoter was found between -130 and -60 base pairs from the major transcription start site. No typical "TATA-like" sequences were found. However, a "GC" box and a "TGTGG" sequence were two potential cis elements required for basal transcription of the porcine gene promoter which shared a 76% sequence identity to the promoter of another GTP-binding protein, the human c-Ha-ras proto-oncogene. Transcription of the gene was inhibited following treatment of renal cells with 10(-8) M dexamethasone.(ABSTRACT TRUNCATED AT 400 WORDS)

An insulin response element in the glyceraldehyde-3-phosphate dehydrogenase gene binds a nuclear protein induced by insulin in cultured cells and by nutritional manipulations in vivo.

Two independent cis-acting insulin response elements (IREs) in the gene encoding glyceraldehyde-3-phosphate dehydrogenase [D-glyceraldehyde-3-phosphate: NAD+ oxidoreductase (phosphorylating), EC 1.2.1.12], designated IRE-A and IRE-B, are sufficient to direct insulin-inducible gene expression. Using the electrophoretic mobility shift assay, a 4-fold increase in the amount of IRE-A DNA bound to nuclear proteins was detected when extracts isolated from insulin-stimulated differentiated 3T3-L1 cells or from the liver of rats refed a high-carbohydrate/low-fat diet after a 72-hr fast were compared to control nuclear extracts. The points of contact between protein and IRE-A DNA may represent a sequence recognized by at least one class of insulin-sensitive transcription factor(s).

Membrane localization of the pertussis toxin-sensitive G-protein subunits alpha i-2 and alpha i-3 and expression of a metallothionein-alpha i-2 fusion gene in LLC-PK1 cells.

The renal epithelial cell line LLC-PK1 has topographically distinct regulatory roles for the alpha subunits of pertussis toxin-sensitive guanine nucleotide regulatory proteins (alpha i subunit); these include the inhibition of adenylyl cyclase at the basolateral membrane and the stimulation of Na+ channel activity at the apical membrane. We now report that LLC-PK1 cells contain two members of the alpha i protein family, alpha i-2 and alpha i-3, which have distinct cellular locations consistent with their diverse functional roles. By using specific alpha i antibodies and immunofluorescence, the alpha i-2 subunit was found to be localized to the basolateral membrane, whereas the alpha i-3 subunit was concentrated in the Golgi and was also detectable at low levels on apical membranes in some cells. Induction of a chimeric mouse metallothionein 1-rat or canine alpha i-2 gene stably transfected into the LLC-PK1 cells produced an increase in the content of the alpha i-2 subunit, which was targeted only to the basolateral membrane. These findings suggest that alpha i subunit specificity for effectors may be achieved in polarized renal epithelial cells by their geographic segregation to different cellular membranes. The LLC-PK1 cell stably transfected with the metallothionein-alpha i-2 fusion gene will provide a model for the study of guanine nucleotide regulatory protein function in epithelia.