Role of tissue-specific transcription factor LFB3 in a cyclic AMP-responsive enhancer of the urokinase-type plasminogen activator gene in LLC-PK1 cells

Regulation of aldosterone synthase by activator transcription factor/cAMP response element-binding protein family members

Aldosterone synthesis is regulated by angiotensin II (Ang II) and K(+) acting in the adrenal zona glomerulosa, in part through the regulation of aldosterone synthase (CYP11B2). Here, we analyzed the role of cAMP response element (CRE)-binding proteins (CREBs) in the regulation of CYP11B2. Expression analysis of activator transcription factor (ATF)/CREB family members, namely the ATF1 and ATF2, the CREB, and the CRE modulator, in H295R cells and normal human adrenal tissue was performed using quantitative real-time PCR. Ang II-induced phosphorylation of ATF/CREB members was analyzed by Western blot analysis, and their subsequent binding to the CYP11B2 promoter using chromatin immunoprecipitation assay. Aldosterone production and CYP11B2 expression were measured in small interfering RNA-transfected cells to knockdown the expression of ATF/CREB members. CYP11B2 promoter activity was measured in H295R cells cotransfected with NURR1 (NR4A2) alone or with constitutively active vectors for ATF/CREB members. Ang II induced phosphorylation of ATF1, ATF2, and CRE modulator in a time-dependent manner. Based on chromatin immunoprecipitation analysis, there was an increased association of these proteins with the CYP11B2 promoter after Ang II and K(+) treatment. Phosphorylated ATF/CREB members also bound the CYP11B2 promoter. Knockdown of ATF/CREB members reduced Ang II and K(+) induction of adrenal cell CYP11B2 mRNA expression and aldosterone production. The constitutively active ATF/CREB vectors increased the promoter activity of CYP11B2 and had a synergistic effect with NURR1. In summary, these results suggest that ATF/CREB and NGFI-B family members play a crucial role in the transcriptional regulation of CYP11B2 and adrenal cell capacity to produce aldosterone.

Expression of hepatocyte nuclear factor-1alpha mRNA in human anaplastic thyroid cancer cell lines and tumors

BACKGROUND

Hepatocyte nuclear factor (HNF)-1alpha and HNF-1beta are related transcription factors that are mainly expressed in liver cells. Our previous study showed that HNF-1beta was highly expressed in papillary thyroid cancer cell lines and tumors. HNF-1alpha mRNA, however, was not detected in differentiated thyroid cancer cell lines. The objective of this study was to determine whether HNF-1alpha is expressed in dedifferentiated anaplastic thyroid cancer cells.

METHODS

Total RNA isolated from six anaplastic thyroid cancer cell lines and 38 surgical samples was analyzed for HNF-1alpha mRNA by conventional reverse-transcription polymerase chain reaction (RT-PCR) or real-time RT-PCR. HNF-1alpha DNA binding activity was measured by gel retardation assay and HNF-1alpha protein was identified by Western blotting.

RESULTS

HNF-1alpha mRNA was expressed in four of the six anaplastic cell lines. The presence of HNF-1alpha protein and DNA binding activity was detected in three lines with higher HNF-1alpha mRNA level. Three cell lines also expressed HNF-1beta. HNF-1alpha transcripts were also detected in five out of six anaplastic tumors, but not in the papillary tumors except one with weak PCR signal.

CONCLUSION

HNF-1alpha mRNA was detected in high frequency in anaplastic thyroid cancer cell lines and tumors. HNF-1alpha might play a role in the pathogenesis of anaplastic thyroid cancer.

Elevation of intracellular cAMP up-regulated thrombomodulin mRNA in cultured vascular endothelial cells derived from spontaneous type-II diabetes mellitus model rat

To investigate whether antihemostatic function of vascular endothelial cells (VECs) is changed in type-II diabetic model rats, the mRNA expressions of tissue-type and urokinase-type plasminogen activator (t-PA and u-PA), thrombomodulin (TM), PA inhibitor type-1 (PAI-1), and phosphodiesterases (type 3A, 3B, and 4D PDEs) were quantitated by the method of comparative reverse transcriptase-polymerase chain reaction (RT-PCR). VECs from type-II diabetic model Otsuka Long-Evans Tokushima Fatty (OLETF) rats and from its normal counterpart (LETO) rats were cultured for 24 h with dibutyryl adenosine 3',5'-cyclic monophosphate (db-cAMP) or a type-3 PDE inhibitor, cilostazol. Intracellular cAMP concentration was determined by the chemiluminescent enzyme-linked immunosorbent assay (ELISA) system. In cultured VECs from OLETF rats, the basal mRNA expressions of u-PA and TM were significantly decreased as compared to those in cultured VECs from LETO rats. TM mRNA expression in cultured VECs from OLETF rats was increased 2.1-fold at 24 h after treatment with db-cAMP (3 mmol/L). Basal mRNA expressions of type 3A, 3B, and 4D PDEs were significantly higher in VECs from OLETF rats than those from LETO rats. After treatment with cilostazol (30 micromol/L), intracellular cAMP was significantly increased at 60 min and TM mRNA expression was increased 1.5-fold at 24 h. Therefore, elevation of intracellular cAMP by db-cAMP or cilostazol up-regulated TM mRNA expression in cultured VECs from OLETF rats.

Parathyroid hormone controls receptor activator of NF-kappaB ligand gene expression via a distant transcriptional enhancer

RANKL, a protein essential for osteoclast development and survival, is stimulated by parathyroid hormone (PTH) via a PTH receptor 1/cyclic AMP (cAMP)/protein kinase A (PKA)/CREB cascade, exclusively in osteoblastic cells. We report that a bacterial artificial chromosome-based transcriptional reporter construct containing 120 kb of RANKL 5'-flanking region was stimulated by dibutyryl-cAMP in stromal/osteoblastic cells, but not other cell types. Full cAMP responsiveness was dependent upon a conserved 715-bp region located 76 kb upstream from the transcription start site, which we identified by sequential deletion analysis and by comparison of human and mouse genomic sequences in silico. This region contained conserved consensus sequences which bound CREB and the osteoblast-specific transcription factor Runx2, and when mutated blunted cAMP responsiveness. Overexpression of Runx2 potentiated cAMP responsiveness of the endogenous RANKL gene in a cell-type-specific manner. Lastly, PTH responsiveness of the endogenous RANKL gene was abrogated in mice from which we deleted this conserved upstream region. Thus, PTH responsiveness of the RANKL gene is determined by a distant regulatory region that responds to cAMP in a cell-type-specific manner and Runx2 may contribute to such cell-type specificity.

Urokinase (u-PA) is produced by collecting duct principal cells and is post-transcriptionally regulated by SV40 large-T, arginine vasopressin, and epidermal growth factor

We have analyzed the expression and regulation of plasminogen activators (PA) in principal cells of the renal collecting duct. We used a rabbit principal cell line (RC.SVtsA58) infected with the temperature-sensitive SV40 strain tsA58. Transformed cells cultured at permissive temperature (33 degrees C) produced only tissue-type plasminogen activator (t-PA). Shifting the cells to nonpermissive temperature (39.5 degrees C) induced their differentiation and a marked increase in total fibrinolytic activity due to the induction of urokinase-type plasminogen activator (u-PA) synthesis and secretion. The effect on u-PA was post-transcriptional and it could be attributed to large-T inactivation at 39.5 degrees C since it was abolished by re-infecting the cells with wild-type SV40. Run-on assay and real-time RT-PCR of u-PA transcripts indicated that large-T altered post-transcriptional regulation. u-PA was also produced by primary cultures of collecting duct cells and was present in the rabbit urine. In the kidney, u-PA and its receptor (u-PAR) were almost exclusively expressed at the apex of collecting duct cells. We then analyzed the regulation of u-PA by arginine vasopressin (AVP) and epidermal growth factor (EGF), two key regulators of principal cell functions. We found that AVP and EGF, which have opposite hydro-osmotic effects in the collecting duct, also exhibited contrasted effects on u-PA synthesis in differentiated RC.SVtsA58 cells. EGF increased but AVP suppressed u-PA activity and protein, and these regulations occurred at post-transcriptional level. These results point to a physiological role of u-PA in principal cells of the renal collecting duct.

Histone deacetylase inhibitor depsipeptide represses nicotinamide N-methyltransferase and hepatocyte nuclear factor-1beta gene expression in human papillary thyroid cancer cells

Nicotinamide N-methyltransferase (NNMT) catalyzes N-methylation of nicotinamide and other structural analogues. NNMT gene expression is enhanced in many papillary thyroid cancer cells and activated by hepatocyte nuclear factor (HNF)-1beta. In this work, we studied the effects of depsipeptide, a histone deacetylase inhibitor, on NNMT gene expression in BHP 18-21 papillary thyroid cancer cells. Depsipeptide reduced NNMT mRNA level in a dose-dependent and time-dependent manner as determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). In contrast, expression of the sodium iodide symporter (NIS), a gene with differentiated function, waas enhanced in the treated cells. NNMT protein level determined by Western blot analysis and NNMT catalytic activity was also reduced significantly in the depsipeptide-treated cells. To study the mechanism of NNMT gene repression by depsipeptide, effects of depsipeptide on NNMT promoter activity were determined by luciferase reporter gene assay. NNMT promoter activity was significantly reduced in the HNF-1beta-positive BHP 18-21 cells but not in the HNF-1beta-negative BHP 14-9 papillary cancer cells. A mutant reporter construct with mutations in a HNF-1 site in the NNMT basal promoter region did not respond to depsipeptide in both HNF-1beta protein levels, and abolished activity of DNA binding to the HNF-1 site in the NNMT promoter region. Protein synthesis inhibitor cycloheximide and proteasome inhibitor MG-132 enhanced HNF-1beta stability in the depsipeptide-treated cells. In summary, depsipeptide represses NNMT and HNF-1beta gene expression in some papillary thyroid cancer cells. the repression of NNMT by depsipeptide is at the transcription level through downregulation of transcription activator HNF-1beta.

What turns CREB on?

The transactivation domain of the cAMP response element-binding protein (CREB) consists of two major domains. The glutamine-rich Q2 domain, which interacts with the general transcription factor TAFII130/135, is sufficient for the recruitment of a functional RNA polymerase II complex and allows basal transcriptional activity. The kinase-inducible domain, however, mediates signal-induced activation of CREB-mediated transcription. It is generally believed that recruitment of the coactivators CREB-binding protein (CBP) and p300 after signal-induced phosphorylation of this domain at serine-133 strongly enhances CREB-dependent transcription. Transcriptional activity of CREB can also be potentiated by phosphoserine-133-independent mechanisms, and not all stimuli that provoke phosphorylation of serine-133 stimulate CREB-dependent transcription. This review presents an overview of the diversity of stimuli that induce CREB phosphorylation at Ser-133, focuses on phosphoserine-133-dependent and -independent mechanisms that affect CREB-mediated transcription, and discusses different models that may explain the discrepancy between CREB Ser-133 phosphorylation and activation of CREB-mediated transcription.

Activation of nicotinamide N-methyltransferase gene promoter by hepatocyte nuclear factor-1beta in human papillary thyroid cancer cells

We previously demonstrated that the human nicotinamide N-methytransferase (NNMT) gene was highly expressed in many papillary thyroid cancers and cell lines. The expression in other papillary and follicular cancers or cell lines and normal thyroid cells was low or undetectable. To gain an understanding of the molecular mechanism of this cell-specific expression, the NNMT promoter was cloned and studied by luciferase reporter gene assay. The promoter construct was expressed highly in papillary cancer cell lines, including those with higher (e.g. BHP 2-7) and lower (e.g. BHP 14-9) NNMT gene expression, and expressed weakly in follicular thyroid cancer cell lines. Further study with 5'-deletion promoter construct suggested that the NNMT promoter was regulated differently in BHP 2-7 and BHP 14-9 cells. In BHP 2-7 cells, promoter activity was dependent on an upstream sequence. In BHP 14-9 cells, sequence in the basal promoter region contributed notably to the overall promoter activity. RT-PCR or Western blot analysis indicated that hepatocyte nuclear factor-1beta (HNF-1beta) was expressed in only papillary cancer cell lines with high NNMT gene expression. HNF-1beta was not expressed or expressed very weakly in other papillary, follicular, and Hurthle cancer cell lines and primary cultures of normal thyroid cells and benign thyroid conditions. A HNF-1 binding site was identified in the NNMT basal promoter region. Mutations in this site decreased NNMT promoter activity in the HNF-1beta-positive BHP 2-7 cells, but not in the HNF-1beta-negative BHP 14-9 cells. HNF-1beta bound to the HNF-1 site specifically as a homodimer as determined by gel retardation assays with HNF-1beta-specific antibody. Cotransfection of a HNF-1beta expression plasmid increased NNMT promoter activity significantly in both HNF-1beta-positive and -negative thyroid cancer cell lines and Hep G2 liver cancer cells. Furthermore, transient expression of HNF-1beta in BHP 14-9 cells increased endogenous NNMT protein levels. In summary, HNF-1beta functions as a transcription activator for NNMT gene expression in some papillary thyroid cancer cells.

Control of the rat angiotensin I converting enzyme gene by CRE-like sequences

We characterized the role of potential cAMP-responsive elements (CRE) in basal and in induced angiotensin converting enzyme (ACE) gene promoter activity in order to shed light on the regulation of somatic ACE expression. We identified stimulators and repressors of basal expression between 122 and 288 bp and between 415 and 1303 bp upstream from the transcription start site, respectively, using a rabbit endothelial cell (REC) line. These regions also contained elements associated with the response to 8BrcAMP. When screening for CRE motifs we found pCRE, a proximal sequence between 209 and 222 bp. dCRE, a distal tandem of two CRE-like sequences conserved between rats, mice and humans, was detected between 834 and 846 bp. Gel retardation analysis of nuclear extracts of REC indicated that pCRE and dCRE bind to the same protein complexes as bound by a canonical CRE. Mutation of pCRE and dCRE in REC established the former as a positive element and the latter as a negative element. In 293 cells, a renal cell line, pCRE and dCRE are negative regulators. Co-transfection of ATF-2 or ATF-2 plus c-Jun repressed ACE promoter activity, suggesting that the ACE gene is controlled by cellular stress. Although mapping of cAMP responsiveness was consistent with roles for pCRE and dCRE, mutation analysis indicated that they were not required for cAMP responsiveness. We conclude that the basal activity of the somatic ACE promoter is controlled by proximal and distal CREs that can act as enhancers or repressors depending on the cell context.

MAPK and JNK transduction pathways can phosphorylate Sp1 to activate the uPA minimal promoter element and endogenous gene transcription

Two upstream regions of the human urokinase (uPA) gene regulate its transcription: the minimal promoter (MP) and the enhancer element. The activity of the minimal promoter is essential for basal uPA transcription in prostate adenocarcinoma PC3 cells. Binding of a phosphorylated Sp1 transcription factor is, in turn, essential for the activity of the MP. Here we report that the Jun kinase (JNK) pathway is required for the basal activity of the MP and for the expression of the endogenous uPA gene in PC3 cells and for activated transcription in LNCaP cells. On the other hand, the p42/p44 mitogen-activated protein kinase (MAPK) pathway activates uPA gene expression through Sp1 phosphorylation in HeLa, LNCaP, and CCL39-derivative cells that do not typically express uPA in basal conditions. In HeLa cells the dominant-negative form of JNK interferes with the p42/p44 MAPK activation of the uPA-MP. The results suggest that the stress-activated protein kinase (SAPK)/JNK pathway plays an important role in the phosphorylation of Sp1, which, in turn, leads to basal or activated transcription from the uPA-MP element.

The coactivator PGC-1 is involved in the regulation of the liver carnitine palmitoyltransferase I gene expression by cAMP in combination with HNF4 alpha and cAMP-response element-binding protein (CREB)

Liver carnitine palmitoyltransferase I catalyzes the transfer of long-chain fatty acids into mitochondria. L-CPT I is considered the rate-controlling enzyme in fatty acid oxidation. Expression of the L-CPT I gene is induced by starvation in response to glucagon secretion from the pancreas, an effect mediated by cAMP. Here, the molecular mechanisms underlying the induction of L-CPT I gene expression by cAMP were characterized. We demonstrate that the cAMP response unit of the L-CPT I gene is composed of a cAMP-response element motif and a DR1 sequence located 3 kb upstream of the transcription start site. Our data strongly suggest that the coactivator PGC-1 is involved in the regulation of this gene expression by cAMP in combination with HNF4 alpha and cAMP-response element-binding protein (CREB). Indeed, (i) cotransfection of CREB or HNF4 alpha dominant negative mutants completely abolishes the effect of cAMP on the L-CPT I promoter, and (ii) the cAMP-responsive unit binds HNF4 alpha and CREB through the DR1 and the cAMP-response element sequences, respectively. Moreover, cotransfection of PGC-1 strongly activates the L-CPT I promoter through HNF4 alpha bound at the DR1 element. Finally, we show that the transcriptional induction of the PGC-1 gene by glucagon through cAMP in hepatocytes precedes that of L-CPT-1. In addition to the key role that PGC-1 plays in glucose homeostasis, it may also be critical for lipid homeostasis. Taken together these observations suggest that PGC-1 acts to coordinate the process of metabolic adaptation in the liver.

In vivo functional characterization of the aldolase B gene enhancer

A 400-bp intronic enhancer fragment in conjunction with the proximal promoter of the aldolase B gene provided correct tissue-specific expression in transgenic mice together with hormonal regulation in the liver. We investigated in vivo and in cultured cells the contribution of the intronic regulatory sequences and their interaction with the promoter elements in controlling aldolase B gene expression. Transgene activity was completely abolished by disruption of the two hepatocyte nuclear factor 1 (HNF1) binding sites in the enhancer, whereas mutation of one HNF1 site had no effect in the liver but strongly decreased activity in the kidney. Our data show that the HNF1 binding site(s) in the enhancer were key regulators of aldolase B transgene expression both in the liver and kidney. Deletion of the CCAAT/enhancer-binding protein site in the promoter completely abolished the enhancer function in HepG2 cells. These results suggest that expression of the aldolase B gene in the liver requires cooperative interactions between CCAAT/enhancer-binding protein and HNF1. Deletion of the HNF4 binding site in the enhancer suppressed expression in both liver and kidney in half of the transgenic lines, suggesting that this element might play a role in chromatin opening at the insertion site. We firmly establish that the endogenous aldolase B gene's first response to glucagon or cyclic AMP exposure was a transient increase in the expression in the liver, followed by a secondary decline in the transcription, as previously reported. This response was reproduced by all transgenes studied, indicating that neither HNF1 nor HNF4 binding sites in the enhancer were involved in this biphasic cyclic AMP response.

Induction of uPA but not NF-IL3A by calcitonin is dependent on Erk1/2 phosphorylation in porcine renal cell line LLC-PK1

Calcitonin (CT) is a polypeptide hormone and has a variety of functions including regulation of urinary calcium excretion. By using a cDNA subtraction hybridization method, we identified that NF-IL3A and urokinase-type plasminogen activator (uPA) genes were up-regulated by CT in porcine renal cell line LLC-PK1. CT-mediated induction of these genes was not inhibited by cycloheximide. These data suggest that these up-regulations are not induced by increased synthesis of regulating proteins; therefore, they are immediately response early (IE). We also found that CT treatment led to the phosphorylation of Erk1/2. We demonstrated that PD98059, a MEK1 inhibitor, inhibited CT-induced mRNA expressions of uPA, but had no obvious influence on the NF-IL3A induction. These results demonstrated the inductions of uPA by CT involve Erk1/2 phosphorylation. We provide the first evidence that NF-IL3A expression is up-regulated by CT. The present findings suggest that the transcriptions of the NF-IL3A and uPA could be induced by CT and might be important mediators of CT function in renal cells.

Differential role of hepatocyte nuclear factor-1 in the regulation of glucose-6-phosphatase catalytic subunit gene transcription by cAMP in liver- and kidney-derived cell lines

In liver and kidney, the terminal step in gluconeogenesis is catalyzed by glucose-6-phosphatase. To examine the effect of the cAMP signal transduction pathway on transcription of the gene encoding the catalytic subunit of glucose-6-phosphatase (G6Pase), G6Pase-chloramphenicol acetyltransferase (CAT) fusion genes were transiently transfected into either the liver-derived HepG2 or kidney-derived LLC-PK cell line. Co-transfection of an expression vector encoding the catalytic subunit of cAMP-dependent protein kinase (PKA) markedly stimulated G6Pase-CAT fusion gene expression, and mutational analysis of the G6Pase promoter revealed that multiple regions are required for this PKA response in both the HepG2 and LLC-PK cell lines. A sequence in the G6Pase promoter that resembles a cAMP response element is required for the full PKA response in both HepG2 and LLC-PK cells. However, in LLC-PK cells, but not in HepG2 cells, a hepatocyte nuclear factor-1 (HNF-1) binding site was critical for the full induction of G6Pase-CAT expression by PKA. Changing this HNF-1 motif to that for the yeast transcription factor GAL4 reduces the PKA response in LLC-PK cells to the same degree as deleting the HNF-1 site. However, co-transfection of this mutated construct with chimeric proteins comprising the GAL4-DNA binding domain ligated to the coding sequence for HNF-1alpha, HNF-1beta, HNF-3, or HNF-4 completely restored the PKA response. Thus, we hypothesize that, in LLC-PK cells, HNF-1 is acting as an accessory factor to enhance PKA signaling through the cAMP response element by altering G6Pase promoter conformation or accessibility rather than specifically affecting some component of the PKA signal transduction pathway.