Promoter region of the human Harvey ras proto-oncogene: similarity to the EGF receptor proto-oncogene promoter

KRAS Promoter Methylation Status and miR-18a-3p and miR-143 Expression in Patients With Wild-type KRAS Gene in Colorectal Cancer

BACKGROUND/AIM

Although some mutations of KRAS proto-oncogene, GTPase (KRAS) have been associated with the prognosis and therapeutic management of colorectal cancer (CRC), the epigenetic mechanisms (DNA methylation and microRNA expression) that regulate wild-type KRAS expression in patients with CRC are poorly known. The aim of this study was to establish whether there is a relationship between the expression of the wild-type KRAS gene, the methylation status of its distal promoter, and miR-143 and miR-18a-3p levels in samples of sporadic CRC.

PATIENTS AND METHODS

A total of 51 cases of sporadic CRC with wild-type KRAS were analyzed. The expression levels of KRAS mRNA, miR-18a-3p, miR-143, and KRAS protein, as well as methylation in the distal promoter of the KRAS gene were evaluated.

RESULTS

In the analyzed cases, KRAS mRNA expression was detected in 51.1%; wild-type KRAS protein was found in the membrane in 31.4% and in the cytoplasm in 98% of cases. An inverse relationship of marginal significance was observed between miR-18a-3p and KRAS protein expression in the cytoplasm (odds ratio=0.14, 95% confidence interval=0.012-1.092; p=0.08). The methylation status of the distal promoter of KRAS at four CpG islands was analyzed in 30 cases (58.8%): partial methylation of the four CpG islands evaluated was observed in two cases (6.7%). In these cases, KRAS protein expression was not evidenced at the membrane level; miR-18a-3p expression was not detected either but high expression of miR-143 was observed.

CONCLUSION

No association was found between the expression levels of KRAS mRNA, miR-18a-3p, miR-143 and methylation status. Methylation status was detected with low frequency, thus being the first report of methylation in wild-type KRAS.

G4 DNA in ras genes and its potential in cancer therapy

It is now well established that in the human genome the canonical double helix coexists with folded G-quadruplex structures that are known to have important biological functions. In this review we summarize the current knowledge on quadruplex formation in the promoters of the ras genes that are mutated in about 30% of all human cancers. We describe the nuclear proteins that recognize these unusual DNA structures and discuss their function in transcription. We also examine the formation of G-quadruplexes in the 5'-untranslated region of the ras transcripts and conclude this review by reporting strategies that use either ras G-quadruplexes or proteins recognizing the ras G-quadruplexes as targets of anticancer small molecules.

Induction of Ras by SAF-1/MAZ through a feed-forward loop promotes angiogenesis in breast cancer

In the majority of breast cancers, overexpression and hyperactivation of Ras in the tumor microenvironment play significant role in promoting cancer cell growth, angiogenesis, and metastasis. We have previously shown that vascular endothelial growth factor (VEGF) expression in triple negative breast cancer cells is regulated, at least in part, by SAF-1 (serum amyloid A activating factor 1) transcription factor. In this study we show that transformation of normal MCF-10A breast epithelial cells by constitutively active, oncogenic Ras, induces the DNA-binding activity and transcription function of SAF-1. Furthermore, we show that inhibition of MEK/MAPK-signaling pathway prevents Ras-mediated activation of SAF-1. Interestingly, silencing of SAF-1 expression in breast cancer cells by SAF-1-specific short hairpin RNAs (shRNAs) significantly reduced H-Ras and K-Ras mRNA level. We show that SAF-1 is a direct transcriptional regulator of H-Ras and K-Ras and overexpression of SAF-1 increases H-Ras and K-Ras gene expression. Chromatin immunoprecipitation (ChIP) analyses demonstrated in vivo interaction of SAF-1 at highly purine-rich sequences present at the proximal promoter region, upstream of the transcription start site, in H-Ras and K-Ras genes. Previous studies have shown that these sequences are nuclease hypersensitive and capable of forming G4 quadruplex structure. Together, our results show the presence of a novel transactivating loop, in which, Ras and SAF-1 are interconnected. These findings will help defining molecular mechanisms of abnormal overexpression of Ras in breast tumors, which seldom show genetic Ras mutations.

HRAS is silenced by two neighboring G-quadruplexes and activated by MAZ, a zinc-finger transcription factor with DNA unfolding property

The HRAS promoter contains immediately upstream of the transcription start site two neighboring G-elements, each capable of folding into a G-quadruplex structure. We have previously found that these G-quadruplexes bind to the zinc-finger transcription factors MAZ and Sp1. In the present study we have examined the interaction between the HRAS promoter and MAZ, demonstrating for the first time that the protein unfolds the G-quadruplex structures. We also demonstrate that MAZ-GST, in the presence of the complementary strands, promotes a rapid transformation of the two HRAS quadruplexes into duplexes. By a mutational analysis of the HRAS G-elements, we dissected the MAZ-binding sites from the quadruplex-forming motifs, finding that the two neighboring G-quadruplexes bring about a dramatic repression of transcription, in a synergistic manner. We also discovered that the two G-quadruplexes are strong targets for small anticancer molecules. We found that a cell-penetrating anthratiophenedione (ATPD-1), which binds tightly to the G-quadruplexes (ΔT > 15°C), promotes the total extinction of HRAS transcription. In contrast, when one of the two G-quadruplexes was abrogated by point mutations, ATPD-1 repressed transcription by only 50%. Our study provides relevant information for the rationale design of targeted therapy drugs specific for the HRAS oncogene.

G4-DNA formation in the HRAS promoter and rational design of decoy oligonucleotides for cancer therapy

HRAS is a proto-oncogene involved in the tumorigenesis of urinary bladder cancer. In the HRAS promoter we identified two G-rich elements, hras-1 and hras-2, that fold, respectively, into an antiparallel and a parallel quadruplex (qhras-1, qhras-2). When we introduced in sequence hras-1 or hras-2 two point mutations that block quadruplex formation, transcription increased 5-fold, but when we stabilized the G-quadruplexes by guanidinium phthalocyanines, transcription decreased to 20% of control. By ChIP we found that sequence hras-1 is bound only by MAZ, while hras-2 is bound by MAZ and Sp1: two transcription factors recognizing guanine boxes. We also discovered by EMSA that recombinant MAZ-GST binds to both HRAS quadruplexes, while Sp1-GST only binds to qhras-1. The over-expression of MAZ and Sp1 synergistically activates HRAS transcription, while silencing each gene by RNAi results in a strong down-regulation of transcription. All these data indicate that the HRAS G-quadruplexes behave as transcription repressors. Finally, we designed decoy oligonucleotides mimicking the HRAS quadruplexes, bearing (R)-1-O-[4-(1-Pyrenylethynyl) phenylmethyl] glycerol and LNA modifications to increase their stability and nuclease resistance (G4-decoys). The G4-decoys repressed HRAS transcription and caused a strong antiproliferative effect, mediated by apoptosis, in T24 bladder cancer cells where HRAS is mutated.

Oligonucleotide treatment of ras-induced tumors in nude mice

Oligonucleotides have shown an ability to target specific oncogene transcripts and inhibit their expression in cells, but the degree to which sustained treatment can suppress the levels of an oncogenic protein enough to benefit a patient remains to be determined. This question has been studied in several ways. First, the relationship of antisense DNA inhibition to the predicted secondary structure of human H-RAS oncogene mRNA was examined in transformed mouse cells that form solid tumors. Inhibition of H-Ras expression was sequence-specific, dose-dependent, and correlated with inhibition of focus formation. The efficacy of the first intron antisense sequence in reducing H-Ras expression was greater than that of the initiation codon target. Second, H-RAS transformed solid tumor cells were pretreated in vitro with normal oligonucleotides, after which tumor growth from the treated cells was tested in nude mice. The three days of treatment with the first intron antisense DNA reduced H-Ras cellular levels by more than 90% whereas a nonspecific control DNA reduced H-Ras levels by approx 20%. Tumor growth of cells treated with H-RAS antisense oligonucleotide was significantly reduced for up to 14 d following the end of treatment and implantation into the mice, whereas the nonspecific control DNA had no significant effect. Third, H-RAS transformed bladder cancer cells were implanted into nude mice, after which the mice were treated for 31 d with oligonucleotide phosphorothioates. Tumor growth in mice treated with H-RAS 12th codon antisense oligonucleotide was reduced by about 80% throughout the treatment period, reiterating the sustained effect seen in pretreated tumor cells. However, the scrambled phosphorothioate control inhibited tumor growth by about 60%, illustrating some nonspecific inhibition. Fourth, K-RAS transformed pancreatic cancer cells were treated in culture and in nude mice. Inhibition of K-Ras expression with a phosphorothioate oligonucleotide directed against a 5'-UTR sequence was sequence-specific and dose-dependent. K-RAS transformed pancreatic cancer cells were implanted into nude mice, after which the mice were treated for 14 d with oligonucleotide phosphorothioates. Tumor growth in mice treated with K-RAS 5'-UTR antisense oligonucleotide was reduced by about 50% throughout the treatment period, reiterating the sustained effect seen with H-RAS transformed cells. In this case, the sense phosphorothioate control did not inhibit tumor growth, demonstrating that nonspecific inhibition is not a characteristic of all phosphorothioate sequences. The next logical steps include testing oligonucleotide efficacy against other tumor types, toxicological testing in higher species, and clinical trials in human subjects.

Structural and functional characterization of the human gene for sorting nexin 1 (SNX1)

The aim of the present study was to identify the gene for sorting nexin 1 (SNX1) to evaluate the potential for tissue-specific alternative splicing and to analyze the activity of the SNX1 promoter. The coding DNA for SNX1 was divided between 15 exons in 43 kb of genomic DNA located on human chromosome 15q22. Although SNX1 mRNA expression was widespread in human tissues, alternative splicing is thought to generate skipped exons in SNX1 cDNAs. By determination of the SNX1 gene structure and an analysis of the mRNAs in a variety of tissues using RT-PCR, we demonstrated that SNX1 mRNAs are alternatively spliced. Exon-skipped products were less abundant than full-length SNX1 mRNA species, but the ratio of skipped to full-length mRNA indicated that alternative splicing may be developmentally regulated in the liver. Consistent with widespread mRNA expression, the SNX1 promoter was GC rich and lacked a TATA box, features characteristic of housekeeping promoters. The promoter activity was dependent on the presence of proximal sequences that contained initiator elements and predicted binding sites for the transcription factors Sp1 and E2F. These findings indicate that regulation of SNX1 gene expression at the transcriptional level is likely minor. Rather, developmentally specific exon skipping provides a potential mechanism for regulating the activity of SNX1.

Structural and functional characterization of liver cell-specific activity of the human sodium/taurocholate cotransporter

Bile salts are rapidly removed from the circulation by the liver-specific sodium/taurocholate cotransporter (SLC10A1). To understand factors controlling its liver-specific expression, we isolated human SLC10A1 from a YAC chromosomal clone. SLC10A1 spans approximately 23 kb distributed over five exons. The major transcription start site is at 299 bp, and a minor start site is at 395 bp from the translational start site. A 1.2-kb portion of the 5' flanking region was sequenced and shown to contain a number of liver-enriched elements, but no TATA box. Using secreted alkaline phosphatase reporter constructs liver-specific expression was examined. Transient transfection demonstrated that SLC10A1 promoter expression was selectively expressed eightfold in FAO and rat hepatocytes, while deletion mutants demonstrated liver-specific expression in a region extending from -5 to +198 bp, which contained putative sites for C/EBP and HNF3. Mutations of the C/EBP site resulted in loss of 77% of transcriptional activity. Cotransfection of C/EBP, but not other putative liver-enriched binding factors, increased SLC10A1 promoter activity. Electrophoretic mobility shift assays demonstrated specific protein-DNA interactions that involved C/EBPalpha and beta. These studies demonstrate that the TATA-less human SLC10A1 promoter exhibits liver-specific activity and its regulatory elements contain binding sites for C/EBP, which contributes specifically to its transcriptional regulation.

Cloning and characterization of the promoter region of the rat epidermal growth factor receptor gene and its transcriptional regulation by nerve growth factor in PC12 cells

Our previous studies have shown that treatment of PC12 cells with nerve growth factor (NGF) causes a profound down-regulation of the epidermal growth factor receptor (EGFR) mRNA and protein. Further, the NGF-induced down-regulation of the EGFR is under transcriptional control. To elucidate the molecular mechanism of this down-regulation we have cloned a 2.7-kilobase sequence from the promoter region of the rat EGFR from a rat P1 library. Six transcriptional start sites were identified by 5'-rapid amplification of cDNA ends and primer extension. Sequence analysis showed a 62% overall homology with the human EGFR promoter region. To investigate its transcription, 1.1 kilobases of the 5'-flanking sequence were fused to a luciferase reporter gene. This sequence exhibited functional promoter activity in transient transfection experiments with PC12, C6, and CV-1 cells. Treatment of PC12 cells with NGF inhibited promoter activity. By transfection of promoter deletion constructs, a silencer element was found between nucleotides -260 and -181, and TCC repeat sequences appeared to be at least partially responsible for the down-regulation of the EGFR by NGF. Supportive evidence for the relevance of this sequence was obtained from gel mobility shift assays and by transfection of TCC mutation constructs. Our results demonstrate that TCC repeat sequences are required for the down-regulation of rat EGFR by NGF in PC12 cells and may lead to the identification of the NGF-responsive transcription factors.

Myeloid cell-lineage and premylocytic-stage-specific- expression of themouse myeloperoxidase gene is controlled at initiation as well as elongation levels of transcription

The myeloperoxidase (MPO) is an important microbicidal protein present at high concentration in the primary granule of mature granulocyte and its expression is regulated in both myeloidcell-lineage and premyelocytic-stage-specific manners. A better understanding of the underlying control mechanisms should provide insights into the temporal and co-ordinate regulation of the gene expression during granulopoiesis. We have identified its promoter by mapping the start(s) of transcription using various molecular approaches together with demonstrating the promoter function of the relevant DNA segment in a transient transfection reporter assay. Besides the major start of transcription mapped at G residue, 11 nucleotide upstream of the 3' end of exon 0, the usage of that is specific to the MPO expressing cell lines, we have shown that irrespective of the MPO-expression status of the hematopoietic cells, transcription occurs broadly within a two kb region upstream of the 5' proximity of the gene, and is largely terminated in intron 2. These data support a model of the premyelocytic-stage-specific MPO expression, the control of which is operated at initiation as well as elongation levels of transcription.

Repression of human fibroblast growth factor 2 by a novel transcription factor

Here we describe the cloning of the regulator of fibroblast growth factor 2 (FGF-2) transcription (RFT) using a yeast one-hybrid screening with a defined motif in FGF-2 promoter as a target sequence. Overexpression of human RFT (RFT-A) reduces FGF-2 RNA and protein levels in both normal and tumor cell lines. Its splice variants, RFT-A' and RFT-B, have deletions in the putative DNA binding domain and fail to bind FGF-2 promoter and repress FGF-2 gene expression. The ratios of RFT isoforms differ between normal and tumor cells, with the splice variants dominating in tumor cells. Overexpression of RFT-A induces glioma cell death. Our data suggest that regulation of FGF-2 by RFT is important for cellular functions and may be impaired in certain tumors.

Cloning and characterization of the promoters of the maxiK channel alpha and beta subunits

Large conductance, calcium-activated potassium (maxiK) channels are expressed in nerve, muscle, and other cell types and are important determinants of smooth muscle tone. To determine the mechanisms involved in the transcriptional regulation of maxiK channels, we characterized the promoter regions of the pore forming (alpha) and regulatory (beta) subunits of the human channel complex. Maximum promoter activity (up to 12.3-fold over control) occurred between nucleotides -567 and -220 for the alpha subunit (hSlo) gene. The minimal promoter is GC-rich with 5 Sp-1 binding sites and several TCC repeats. Other transcription factor-binding motifs, including c/EBP, NF-kB, PU.1, PEA-3, Myo-D, and E2A, were observed in the 5'-flanking sequence. Additionally, a CCTCCC sequence, which increases the transcriptional activity of the SM1/2 gene in smooth muscle, is located 27 bp upstream of the TATA-like sequence, a location identical to that found in the SM1/2 5'-flanking region. However, the promoter directed equivalent expression when transfected into smooth muscle and other cell types. Analysis of the hSlo beta subunit 5'-flanking region revealed a TATA box at position -77 and maximum promoter activity (up to 11.0-fold) in a 200 bp region upstream from the cap site. Binding sites for GATA-1, Myo-D, c-myb, Ets-1/Elk-1, Ap-1, and Ik-2 were identified within this sequence. Two CCTCCC elements are present in the hSlo beta subunit promoter, but tissue-specific transcriptional activity was not observed. The lack of tissue-specific promoter activity, particularly the finding of promoter activity in cells from tissues in which the maxiK gene is not expressed, suggests a complex channel regulatory mechanism for hSlo genes. Moreover, the lack of similarity of the promoters of the two genes suggests that regulation of coordinate expression of the subunits does not occur through equivalent cis-acting sequences.

Role of far upstream repressor elements controlling proto-Ha-ras gene transcription

The far upstream region of the rat Ha-ras gene has been characterized to determine whether possible repressor sequences may control the low level of Ha-ras gene transcription from its TATA-less, GC-rich strong promoter. The chloramphenicol acetyl transferase (CAT) gene under the control of the 3.8-kb Ha-ras upstream promoter was minimally expressed in HeLa cells. Surprisingly, CAT gene expression was increased by the deletion of a 0.7-kb BglII fragment containing non-coding exon minus 2 and TATA box promoter elements located 1.7 kb upstream of the GC-rich strong promoter. Far upstream (CA)25 repeats also appeared to repress Ha-ras gene activity. Sequences within the 0.7-kb BglII fragment suppressed CAT gene expression when placed upstream of a heterologous thymidine kinase (tk) gene promoter. Repressor activity was further localized to a 160-bp AvrII-BglII sub-fragment. Gel shift assays identified two sequence-specific DNA binding proteins. The results demonstrated for the first time that far upstream repressor sequences control normal transcription of the Ha-ras proto-oncogene.

Transcriptional regulation of the generic promoter III of the rat prolactin receptor gene by C/EBPbeta and Sp1

Three promoters are operative in the rat prolactin receptor gene as follows: promoter I (PI) and II (PII) are specific for the gonads and liver, respectively, and promoter III (PIII) is common to several tissues. To investigate the mechanisms controlling the activity of promoter III, its regulatory elements and transcription factors were characterized in gonadal and non-gonadal cells. The TATA-less PIII domain was localized to the region -437 to -179 (ATG +1) containing the 5'-flanking region and part of the non-coding first exon. Within the promoter domain, a functional CAAT-box/enhancer binding protein (C/EBP) (-398) and an Sp1 element (-386), which bind C/EBPbeta and Sp1/Sp3, respectively, contribute individually to promoter activation in gonadal and non-gonadal cells. However, significant redundancy was demonstrated between these elements in non-gonadal cells. Additionally, an element within the non-coding exon 1 (-338) is also required for promoter activity. Activation of PIII by the widely expressed Sp1 and C/EBPbeta factors explains its common utilization in multiple tissues. Moreover, whereas the rat and mouse PIII share similar structure and function, the mouse PI lacks the functional SF-1 element and hence is inactive. These findings indicate that promoter III is of central importance in prolactin receptor gene transcription across species.

Structure and function of the human Werner syndrome gene promoter: evidence for transcriptional modulation

The Werner syndrome (WS) is an autosomal recessive segmental progeroid syndrome caused by mutations in a novel member ( WRN ) of the RecQ family of helicases. Somatic WS cells are hypermutable and have elongated S phases, suggesting possible defects in DNA replication and/or repair. As an initial approach to the investigation of how this locus might be responsive to DNA damage, we determined the structure of the human WRN promoter. The WRN promoter region has two transcription initiation sites and exhibits several features characteristic of so-called constitutive promoters, including the absence of TATA and CAAT boxes. A luciferase reporter assay revealed that the upstream promoter was used 2-10-fold less frequently than the downstream promoter, the variation being a function of cell type. The activity of the WRN promoter was dramatically reduced in cells from WS patients. The reduction of activity was not seen in three other promoters tested, including one TATA-less promoter and one TATA-containing promoter. This is consistent with the presence of a positive regulatory mechanism of WRN expression.

Organization and alternative splicing of the murine phospholipase D2 gene

Phospholipase D (PLD) catalyses the hydrolysis of phosphatidylcholine, generating phosphatidic acid and choline. Mammalian PLD activity derives from a family of membrane-associated enzymes that are activated by a wide variety of signal transduction events. cDNA species encoding human, mouse and rat PLD1 and PLD2 have recently been reported. In this study we undertook to determine the organization of the mouse PLD2 gene. We report that the gene spans 17.1 kb and contains 25 exons. Mouse PLD2 is notable for a relatively GC-rich and large 5' untranslated region. Proximal promoter sequences upstream of the first exon contain several consensus SP1 sequences (GGGCGG) but lack TATA and CAAT boxes. Finally, alternatively spliced cDNA species identified for PLD1 and PLD2 are discussed in the context of the PLD2 genomic organization.

The mouse chondroadherin gene: characterization and chromosomal localization

The mouse chondroadherin gene was isolated from a cosmid genomic library by the use of a rat chondroadherin cDNA probe. Southern blot analysis of mouse genomic DNA revealed a simple pattern of hybridization indicating a single copy gene for chondroadherin. The mouse chondroadherin gene encompasses 4.1 kb and consists of four exons separated by one large intron of 1929 bp followed by two smaller introns of 247 and 225 bp, respectively. Most of the translated region, including the start codon and the main part of a leucine-rich region, is contained within the first exon. Two small exons of 164 and 146 bp encode the rest of the protein. Interestingly, 4 bases from the stop codon, in the 3'-UTR, a third intron is located. A putative promoter region of 669 bp was sequenced and shown to contain a potential TATAA-box signal 29 bp upstream of the transcription start site and several recognition sites for transcription factors. The exon/intron organization of the chondroadherin gene differs from those of the other known genes of the leucine-rich repeat (LRR) family in the extracellular matrix. Taken together with comparison of protein sequences of other members of the LRR family in the extracellular matrix, the data suggest that chondroadherin has evolved along a different pathway. The chondroadherin gene was mapped to mouse chromosome 11, near D11Mit14, by single-strand conformation polymorphism linkage analysis.

Molecular cloning and characterization of the human mitochondrial 2,4-dienoyl-CoA reductase gene (DECR)

2,4-Dienoyl-CoA reductase (EC 1.3.1.34) is an auxiliary enzyme of beta-oxidation, and it participates in the metabolism of unsaturated fatty enoyl-CoA esters having double bonds in both even- and odd-numbered positions. In this article we describe the molecular cloning of the human gene for the 120-kDa isoform of mitochondrial 2,4-dienoyl-CoA reductase (DECR). The gene is approximately 30 kb and comprises 10 exons varying in size from 79 to 203 bp and 9 introns whose sizes vary from 95 bp to about 10 kb. The 5' UTR and 3' UTR are included in exons 1 and 10, respectively. The promoter region contains putative binding sites for several transcription factors, e.g., Sp1, AP-2, AP-4, and C/EBP, but no TATA box was found. Primer extension analysis and 5' RACE-PCR revealed variability in the length of the 5'-UTR, the longest being 72 bp. Through the use of FISH analysis on metaphase chromosomes with a genomic fragment of 2,4-dienoyl-CoA reductase, the gene was assigned to the chromosomal band 8q21.3.

H-ras oncogene activation in invasive UVR-induced corneal sarcomas of the opossum Monodelphis domestica

Chronic exposure to ultraviolet radiation (UVR) induces corneal sarcomas in the South American opossum Monodelphis domestica. Cell lines are readily established from these tumors. Northern blotting of mRNA from six such cell lines revealed high expression of the H-ras oncogene. H-ras cDNA from an eye tumor cell line was cloned and characterized; the germline sequence of codons 12, 13, and 61 was confirmed by examination of H-ras sequences amplified from liver DNA by the polymerase chain reaction. The Monodelphis H-ras coding sequence is 84-89% identical to that of other vertebrates at the nucleotide level, and the predicted 189-amino-acid sequence differs by 2-12 amino acids from that of other vertebrates. Analysis of 12 primary invasive corneal sarcomas induced by chronic UVR exposure revealed no evidence of H-ras gene amplification or rearrangement. One tumor was heterozygous for an activating point mutation in codon 61 of the H-ras gene; the tumor was also homozygous for a point mutation at an adjacent site in codon 62. These results provide additional evidence for the functional importance and consequent evolutionary conservation of the ras oncogenes.

A splicing enhancer in the 3'-terminal c-H-ras exon influences mRNA abundance and transforming activity

Analysis of cDNA clones previously identified an optional intron in the 3'-untranslated region of the human H-ras gene. A possible correlation was observed between failure to remove this intron and overexpression of the gene, suggesting that splicing of the intron may require a specific titrable factor. The splicing signals at the end of the intron deviate from the consensus and may be inefficient, but we noticed that the adjacent exon downstream has a purine-rich region reminiscent of purine-rich splicing enhancers in other genes that stimulate the removal of weak, flanking introns. We show here that the purine-rich region of H-ras has splicing-enhancer activity in the homologous as well as a heterologous context. Interestingly, although the affected intron is outside the coding region, inversion or deletion of the enhancer reduced the transforming activity of oncogenic H-ras alleles severalfold. Experiments with corresponding cDNA constructs suggested that this is not a consequence of the altered structures of the mRNAs produced when the enhancer is inverted or deleted. Instead, we propose that the region controls an additional pre-mRNA processing event besides splicing of the terminal intron. Our work indicates that the purine-rich region may play an important role in the control of H-ras activity.

Structural organization and characterization of the promoter region of the rat gonadotropin-releasing hormone receptor gene

The gene encoding the rat gonadotropin-releasing hormone (GnRH) receptor was isolated, and its structural organization and promoter region were characterized. The gene was found to consist of three exons that encode the receptor protein, and spanned about 20 kb. Of two genomic clones analyzed, one contained the 5'-untranslated region and the first exon, and the other contained the second and third exons. The sizes of the first, second, and third exons are 625, 217, and 1476 nt, respectively. The first intron is at least 12 kb in length and is located between nucleotides 522 and 523 of the cDNA reading frame, in the middle of the fourth transmembrane domain. The second intron is about 2.5 kb and is also located in the reading frame between nucleotides 739 and 740, separating the fifth and sixth transmembrane domains. Genomic blots in combination with cloning and sequencing suggested that a single GnRH receptor gene is present in the rat genome. Primer extension indicated that the transcription start site is located 103 nt upstream of the translational start codon. A putative TATA box is positioned 23 nt in front of the transcription initiation site. The 1.8 kb 5' flanking sequence contains an SF-1 site, an AP-1 site, CCAAT sequences, a Pit-1 binding site, and a potential CRE-like sequence. To evaluate promoter activity, the 1.8 kb and two 5' deleted fragments of 1.2 and 0.6 kb were fused to the luciferase reporter gene and transiently expressed in immortalized pituitary gonadotrophs (alphaT3-1 cells) and hypothalamic neurons (GT1-7 cells), and in nonpituitary (COS-7) cells. Luciferase gene expression was significantly increased by all three fragments in pituitary and hypothalamic cells, but not in COS-7 cells. The promoter activity of the 1.2 kb fragment was higher than that of the other fragments. Forskolin and cAMP analogs increased luciferase gene expression in both alphaT3-1 and GT1-7 cells, but activation of protein kinase C by phorbol myristate acetate had no effect. These studies indicate that positive and negative regulatory elements are present within the 1.8 kb 5' flanking sequence of the GnRH receptor. Knowledge of the genomic organization and analysis of the promoter region of the rat GnRH receptor gene will facilitate the elucidation of its transcriptional control in pituitary gonadotrophs and hypothalamic neurons.

Effects of hypoxanthine substitution on bleomycin-mediated DNA strand degradation in DNA-RNA hybrids

We have reported on the differences in site-specific cleavage between DNA and DNA-RNA hybrids by various prototypic DNA cleavers (accompanying paper). In the case of bleomycin (BLM), degradation at 5'-GC-3'sites was suppressed relative to the same sequence in double-stranded DNA, while 5'-GT-3' damage remained constant. We now present results of our further investigation on the chemical and conformational factors that contribute to BLM-mediated DNA strand cleavage of DNA-RNA hybrids. Substitution of guanine by hypoxanthine on the RNA strand of hybrids resulted in a significant enhancement of 5'-GC-3' site damage on the DNA strand relative to double-stranded DNA, thus reversing the suppression noted at these sites. Additionally, 5'-AT-3' sites, which are damaged significantly more in the hybrid than in DNA, exhibit decreased product formation when hypoxanthine is present on the RNA strand of hybrids. However, when hypoxanthine is substituted for guanine on the DNA strand (a GC cleavage site becomes IC), 5'-IT-3' and 5'-IC-3' site cleavage is almost completely suppressed, whereas AT site cleavage is dramatically enhanced. The priority in metallobleomycin site-specific cleavage of hybrids changes with hypoxanthine substitution: the cleavage priority is AT > GT > GC in native hybrid; GC > GT > AT in hybrids substituted with hypoxanthine in the RNA strand; AT >> GT approximately GC in hybrids substituted with hypoxanthine in the DNA strand. The results of kinetic isotope effect studies on BLM cleavage are presented and, in most cases, the values are larger for the hypoxanthine-substituted hybrid. The results suggest that the 2-amino groups of guanine residues on both strands of the nucleic acid play an important role in modulation of the binding and cleavage specificity of BLM.

The human basonuclin gene

The human gene for basonuclin, a zinc-finger protein of keratinocytes, has been cloned, sequenced and assigned to chromosome 15. The transcription unit spans nearly 29 kb of sequence. The coding region is distributed over five exons, and the three pairs of zinc fingers are encoded by the last two. The 5' flanking sequence and first exon are unusually rich in G+C and in CpG dinucleotides. This region contains numerous target sites for the transcription factor Sp1.

Genomic organization of the mouse double minute 2 gene

Transfection of the mouse double minute 2 (Mdm2) oncogene has been found to induce immortalization of primary cells and to transform cultured cells. Amplification and/or overexpression of human MDM2 has been documented in a large percentage of human cancers. Mouse and human Mdm2 cDNA have been cloned from transformed cells and the cDNA sequence of both genes have been reported previously. In this report, we present the gene structure of mouse Mdm2. Comparison of the coding sequences of the Mdm2 gene with the previously reported cDNA sequence and with Mdm2 sequences obtained from an Mdm2-bearing cosmid clone capable of inducing transformation revealed that the reported cDNA sequence was in error, and that Mdm2-induced transformation of cells does not require an activating mutation in Mdm2. Ligation-anchor PCR analysis of transcripts produced from the P1 and P2 promoters indicates that transcription initiates at sites upstream of those reported previously for both promoters.

Organization of the gene encoding transcriptional repressor deltaEF1 and cross-species conservation of its domains

DeltaEF1 (delta-crystallin/E2-box factor 1) is a widely distributed repressor of transcription which binds at the E2-box sequence, CACCTG. It carries seven zinc fingers (Zf) in two clusters and a homeodomain in the middle as potential DNA-binding domains. We cloned the genomic gene encoding chicken deltaEF1 and analyzed its organization. The gene consisted of nine exons, the N-proximal Zf were encoded by exons 5 through 7, and the C-proximal Zf by exons 8 and 9. Exon 7 also coded for the large middle portion of the protein including the homeodomain. Promoter analysis and RNase-protection assay indicated that the gene is driven by a G+C-rich promoter without a TATA box, and the transcription start points (tsp) cluster around 20 bp from the start codon located in exon 1. cDNA and genomic sequences of the mouse delta EF1 were cloned and compared with the chicken sequence. The deduced amino acid (aa) sequence was highly conserved between the chicken and mouse deltaEF1, no only in DNA-binding motifs but also in other blocks (78% overall aa identity). More recently reported DNA-binding proteins, AREB6 (human) ZEB (human) and BZP (hamster), were attributed to homologues of deltaEF1, among which only AREB6 represented full-length sequence. It was also indicated that rodent deltaEF1 lacked exon 3.

Molecular cloning and characterization of a mouse nuclear orphan receptor expressed in embryos and testes

A mouse cDNA encoding a putative DNA-binding protein of the zinc-finger type was isolated from an E8.5 mouse embryonic cDNA library. Sequence comparison revealed a high degree of homology between this mouse cDNA and the human and rat orphan receptor Tr2-11 isolated from prostate cDNA libraries. This transcript was detected in early-to-midgestation embryos and was seen to level off during later stages of development. In adult animals, a high level of expression was detected only in the testis, starting at postnatal day 18, a stage when active meiosis begins to occur. A specific antibody was raised, and immunoreactive signal was specifically located in the adlumenal compartment of the seminiferous tubule, where advanced germ cells reside. In mice fed a vitamin A-depleted diet, where the testes were depleted of advanced germ cells, expression of this protein could not be detected, suggesting a biological relation of this orphan receptor and male germ-cell differentiation. Using a retinoic acid response element (RARE)-containing reporter system, it was demonstrated that expression of this protein dramatically repressed both the basal and the retinoic acid (RA)-regulated promoter activities of this reporter. Thus, this orphan receptor could play a role in modulating both the basic transcription machinery and the RA signalling pathway during embryogenesis and male germ-cell differentiation.

Cloning and characterization of a functional promoter of the rat pp120 gene, encoding a substrate of the insulin receptor tyrosine kinase

Cloning of the 5 -flanking region of the rat pp120 gene has indicated that it is a housekeeping gene: it lacks a functional TATA box and contains several Sp1 binding sites and multiple transcription initiation sites at nucleotides -101, -71, -41, and -27 spread over a GC-rich area. A fragment between nucleotides -21 and -1609 exhibited promoter activity when ligated in a sense orientation into a promoterless luciferase reporter plasmid and transiently transfected into rat H4-II-E hepatoma cells. 5' progressive deletion and block substitution analyses revealed that the three proximal Sp1 boxes (boxes 3, 5, and 6) are required for basal transcription of the pp120 gene. Promoter activity was stimulated 2-3-fold in response to insulin, dexamethasone, insulin plus dexamethasone, and cAMP. Although unaltered by phorbol esters alone, promoter activity was stimulated 4-5-fold in response to phorbol esters plus cAMP. Several motifs resembling response elements for insulin (in the rat phosphoenolpyruvate carboxykinase gene), glucocorticoids, cAMP, and phorbol esters as well as a number of putative binding sites for activating proteins-1 (Jun/Fos) and -2, and liver-specific factors were detected. The role of these sites in tissue-specific expression of pp120 remains to be investigated.

Promoter and upstream regulatory activities of the mouse cellular retinoic acid-binding protein-I gene

The promoter and its upstream regulatory region of the mouse cellular retinoic acid-binding protein I (crabp-I) gene were examined in transgenic mouse embryos, a mouse embryonal carcinoma cell line P19, and a mouse embryonic fibroblast cell line 3T6. In transgenic mouse embryos, a beta-galactosidase reporter gene under the control of crabp-I promoter and its upstream regulatory region displayed a very specific pattern of expression characteristic of crabp-I gene expression during developmental stages. In tissue culture systems, the minimal promoter of this gene was identified, and regions containing positive and negative regulatory activities were dissected from the upstream 3-kilobase sequence using assays for transient reporter activity. It is concluded that the minimal promoter of the mouse crabp-I gene is located between 120 and 150 base pairs upstream from the transcription initiation site. Several cell type-specific positive and negative regulatory regions for this promoter have been identified. A region encoding a common negative regulatory activity in both P19 and 3T6 cells is also inhibitory to two heterologous promoters, and specific protein-DNA interactions between this DNA fragment and nuclear extracts of P19 and 3T6 are demonstrated by gel retardation experiments.

Pancreatic islet expression of the homeobox factor STF-1 relies on an E-box motif that binds USF

The commitment of cells to specific lineages during development is determined in large part by the relative expression of various homeodomain (HOX) selector proteins, which mediate the activation of distinct genetic programs. But the mechanisms by which individual HOX genes are themselves targeted for expression in different cell types remain largely uncharacterized. Here, we demonstrate that STF-1, a homeodomain protein that functions in pancreatic morphogenesis and in glucose homeostasis is encoded by an "orphan" homeobox gene on mouse chromosome 5. When fused to a beta-galactosidase reporter gene, a 6.5-kilobase genomic fragment of 5'-flanking sequence from the STF-1 gene shows pancreatic islet specific activity in transgenic mice. Two distinct elements within the STF-1 promoter are required for islet-restricted expression: a distal enhancer sequence located between -3 and -6.5 kilobases and a proximal E-box sequence located at -104, which is recognized primarily by the helix loop helix/leucine zipper nuclear factor USF. As point mutation within the -104 E-box that disrupt USF binding correspondingly impair STF-1 promoter activity, our results demonstrate that USF is an important component of the regulatory apparatus which directs STF-1 expression to pancreatic islet cells.

Hypomethylation of DNA: a nongenotoxic mechanism involved in tumor promotion

There is an abundant amount of information on the mechanisms of action of genotoxic chemicals that act as carcinogens and the role that mutations play in carcinogenesis. However, carcinogenesis is more than mutagenesis and many carcinogens are not mutagens. Thus, there is a need to consider nongenotoxic mechanisms that may be involved in carcinogenesis. In this paper, we review our working hypothesis that hypomethylation of DNA is an epigenetic, nongenotoxic mechanism that plays a role in tumor promotion by facilitating aberrant gene expression. The utility of employing experimental models that focus on relevant comparisons between sensitive and resistant strains of mice is emphasized. Additionally, aspects of DNA methylation in rodents and humans are compared and contrasted. We discuss hypomethylation of DNA as a secondary mechanism, that is expected to be threshold-exhibiting, and conclude by describing how this information may facilitate a rational approach towards risk assessment when dealing with nongenotoxic compounds that are carcinogenic in a bioassay.

The mouse p44 mitogen-activated protein kinase (extracellular signal-regulated kinase 1) gene. Genomic organization and structure of the 5'-flanking regulatory region

Mitogen-activated protein kinase (MAPK) or extracellular signal-regulated kinase are ubiquitous kinases conserved from fungi to mammals. Their activity is regulated by phosphorylation on both threonine and tyrosine, and they play a crucial role in the regulation of proliferation and differentiation. We report here the cloning of the murine p44 MAP kinase (extracellular signal-regulated kinase 1) gene, the determination of its intron/exon boundaries, and the characterization of its promoter. The gene spans approximately eight kilobases (kb) and can be divided into nine exons and eight introns, each coding region exon containing from one to three of the highly conserved protein kinase domains. Primer extension analysis reveals the existence of two major start sites of transcription located at -183 and -186 base pairs (bp) as well as four discrete start sites for transcription located at -178, -192, -273, and -292 bp of the initiation of translation. However, the start site region lacks TATA-like sequences but does contain initiator-like sequences proximal to the major start sites obtained by primer extension. 1 kb of the promoter region has been sequenced. It contains three putative TATA boxes far upstream of the main start sites region, one AP-1 box, one AP-2 box, one Malt box, one GAGA box, one half serum-responsive element, and putative binding sites for Sp1 (five), GC-rich binding factor (five), CTF-NF1 (one), Myb (one), p53 (two), Ets-1 (one), NF-IL6 (two), MyoD (two), Zeste (one), and hepatocyte nuclear factor-5 (one). To determine the sites critical for the function of the p44 MAPK promoter, we constructed a series of chimeric genes containing variable regions of the 5'-flanking sequence of p44 MAPK gene and the coding region for luciferase. Activity of the promoter, measured by its capacity to direct expression of a luciferase reporter gene, is strong, being comparable with the activity of the Rous sarcoma virus promoter. Progressive deletions of the approximately 1 kb (-1200/-78) promoter region allowed us to define a minimal region of 186 bp (-284/-78) that has maximal promoter activity. Within this context, deletion of the AP-2 binding site reduces by 30-40% the activity of the promoter. Further deletion of this minimal promoter that removes the major start sites (-167/-78) surprisingly preserves promoter activity. This result implicates a major role of this region that contains the Sp1 sites.(ABSTRACT TRUNCATED AT 400 WORDS)

Differentiation-associated expression of the proto-oncogene pim-1 in cultured human keratinocytes

The proto-oncogene pim-1 was expressed in nine human tissues (including epidermis) examined by Northern blotting. Expression of pim-1 was also observed in a number of carcinoma-derived keratinocyte lines in addition to strains derived from normal epidermis. With the exception of a squamous carcinoma line that exhibits little differentiated character in culture (SCC-4), where it was not detected, pim-1 expression was substantially higher after confluence than during log-phase growth in each case. The differentiation marker keratinocyte transglutaminase showed the same pattern of expression as pim-1 in relation to confluence in each of the cell lines and strains studied. The influences on pim-1 mRNA levels of several known effectors of keratinocyte differentiation were studied in the squamous carcinoma line SCC-9. pim-1 mRNA was stimulated by hydrocortisone and suppressed by the tumor promoter tetradecanoyl phorbol acetate. pim-1 mRNA was also regulated by calcium ion concentration in the culture medium, with expression being threefold higher in 0.15 mM than in 0.03 mM calcium ion. Keratinocyte transglutaminase was regulated similarly by these effectors. Thus pim-1 expression was associated with keratinocyte differentiation in these cultured cells.

Organization and promoter analysis of the mouse dishevelled-1 gene

We have characterized the genomic organization of a mouse homolog (Dvl-1) of Drosophila dishevelled, a segment polarity gene required for wingless signal transduction. The Dvl-1 gene is organized into 15 exons ranging in size from 68 to 1315 bp spanning a region of 12,409 bp, with the largest and smallest intron being 5545 and 71 bp, respectively. Sequence analysis of the 5'-flanking region of the gene revealed a high GC content, six CCGCCC Sp-1-binding motifs, CREB, LBP-1 (leader-binding protein 1), and TGGCA-binding consensus sites. However, neither TATA or CAAT boxes are present, a characteristic shared by other GC-rich promoters. The 5'-flanking region has strong promoter activity when placed upstream of the luciferase gene. Promoter-luciferase constructs have demonstrated that the promoter is functional in transfection assays and that its activity is orientation dependent. Promoter deletions were used to define the 5' and 3' boundaries for promoter activity and revealed the presence of both positive and negative regulatory elements. Multiple transcription initiation sites were mapped by primer extension analysis and confirmed by reporter gene assay.

Structure of the rat V1a vasopressin receptor gene and characterization of its promoter region and complete cDNA sequence of the 3'-end

The gene encoding the rat V1a arginine vasopressin (AVP) receptor was isolated, and its structural organization and 5'-flanking region were characterized. In addition, the complete cDNA sequence of the major transcript of the rat V1a receptor gene was determined. Southern blots demonstrated a single copy of the V1a receptor gene in the rat genome, spanning a region of 3.8 kilobases (kb) and consisting of two exons and one intron (1.8 kb). The location of the intron was unique among G protein-coupled receptor genes in that the first exon encodes six of the seven transmembrane regions, the seventh region being encoded by the second exon. Primer extension, RNase protection, and rapid amplification of the 5'-end of the cDNA identified three transcriptional initiation sites (-405, -243, and -237), the major transcription initiation sites being mapped to positions -243 and -237 base pairs (bp) upstream of the ATG initiation codon (+1 bp). This portion of the 5'-flanking region has neither a TATA nor a CCAAT box, is GC-rich but has no GC box motif, and has features of promoters seen in housekeeping genes. Chimeras containing 2.2 kb of the 5'-flanking region and deletion analyses using the chloramphenicol acetyltransferase gene indicated that a "minimal" region, exhibiting promoter activity and tissue specificity, is located between nucleotides -296 and -221, when transfected into vascular smooth muscle cells. Gel mobility shift assay and Southwestern blotting suggested that approximately 30- and approximately 28-kDa nuclear proteins specifically bind to this region. Rapid amplification of the 3'-end of the cDNA showed that the major transcript terminates 442 bp downstream of the stop codon, in agreement with the mRNA size (2.1 kb). This study demonstrated a distinctive feature in the structural organization of the AVP-oxytocin receptor family genes, and characterization of the 5'-flanking region reported here will lead to a better understanding of the mechanism of transcriptional regulation of the rat V1a AVP receptor gene.

Human herpesvirus 6A ts suppresses both transformation by H-ras and transcription by the H-ras and human immunodeficiency virus type 1 promoters

Human herpesvirus 6 strain U1102 (HHV-6A) was shown to contain a 1,473-bp functional transformation suppressor gene (ts). ts exhibited 24% identity and 51% similarity to adeno-associated virus type 2 Rep68/78. Like adeno-associated virus type 2 Rep68/78, HHV-6A ts suppressed H-ras transformation of NIH 3T3 cells. Suppression of H-ras transformation was eliminated by translation termination linker mutation at amino acid 25, 125, or 245. These data indicated the importance of the C-terminal portion of the ts protein. H-ras transformation was suppressed by ts only when H-ras was expressed by its endogenous H-ras promoter and not when it was expressed by the heterologous murine osteosarcoma virus long terminal repeat (LTR). Furthermore, ts suppressed chloramphenicol acetyltransferase (CAT) activity when the CAT gene was expressed from the H-ras promoter but not the murine osteosarcoma virus LTR promoter. Taken together, the data showed that ts suppressed H-ras transformation at the level of the H-ras promoter. To further identify the interaction of ts with transcriptional regulatory elements, the human immunodeficiency virus type 1 (HIV-1) LTR was used. This promoter was selected because it has well-defined transcriptional regulatory elements for both basal and activated transcription, because its activity is inhibited by the Rep68/78 gene, and because both HHV-6 and HIV-1 naturally infect CD4+ T cells in vivo and have been shown to infect the same cell in vitro. ts suppressed expression from both wild-type and upstream mutant HIV-1 LTR-CAT constructs. However, downstream HIV-1 TAR mutations reversed ts suppression, indicating that TAR is one of the critical elements involved. The data presented demonstrated that HHV-6A ts functionally suppressed H-ras transformation and HIV-1 LTR expression and thus that it may be useful in future gene therapy.

Structure of the mouse dipeptidyl peptidase IV (CD26) gene

Dipeptidyl peptidase IV (DPP IV, EC 3.4.14.5) is an ectopeptidase whose expression is modulated during thymocyte differentiation and T cell activation. We describe here the organization of the mouse DPP IV gene. This gene, which encompasses more than 90 kb, is composed of 26 exons separated by introns, the lengths of which vary from 100 bp to more than 20 kb. Reverse PCR performed on RNA from different tissues indicated that DPP IV transcripts do not contain alternatively spliced CDS sequences and, therefore, are supposed to yield a single polypeptide. However, two types of specific mRNA have been detected that differ in their 3'UTR sequences. They derive from alternative polyadenylation of the DPP IV primary transcript, since the different 3'UTR sequences are contiguous in the mouse DPP IV gene. Sequence analysis of the gene 5'-flanking region revealed several structural features found in the TATAA-box-less promoters, including a G+C-rich segment, a high frequency of dinucleotide CpG, and an imperfect symmetrical dyad. The DPP IV gene was assigned by in situ hybridization to the mouse [2C2-2D] region, which is syntenic with human chromosome 2. These data indicate that the human Dpp4 locus is located within this synteny region (i.e., 2q14-q37). The genomic organization of the mouse DPP IV gene is compared to that of classical serine proteases and serine hydrolases. As structural and mechanistic conservation in the absence of sequence similarity is the most remarkable feature among alpha/beta hydrolases [Ollis, D. L., et al. (1992) Protein Eng. 5, 197-211], we report the possible evolutionary link between the DPP IV related family and alpha/beta hydrolases.

Identification of multiple promoters within the N-ras proto-oncogene

N-ras possesses a 'housekeeping' promoter, being G + C-rich and devoid of a TATA-box. Transcription initiates at a number of locations within this gene, a phenomena that is generally attributed to the absence of a TATA-box. In this report we investigate the possibility that multiple promoters, which could potentially contribute to the observed 5' end heterogeneity, exist within the murine N-ras gene. The 5' region of the gene was subdivided into several fragments, each corresponding to a region in which one or more transcription initiation site(s) had been mapped, and the ability of each fragment to express a reporter gene was assessed. Promoter activity was found associated with three independent, non-overlapping fragments, two of which were located entirely within transcribed regions of the gene. We found that these intragenic promoters were able to express the N-ras gene itself, as well as the reporter gene. In addition, we found that the activity of an intragenic promoter fragment was dependent upon the presence of regions encompassing initiation sites, and that a small fragment (approximately 40 bp) encompassing several initiation sites possessed promoter activity. These data support the existence of an 'initiator' element within the N-ras gene. Overall, our results demonstrate that multiple promoters reside within N-ras and suggest that they may play a role in generating the observed mRNA 5' end heterogeneity. The identification of multiple promoters within N-ras may have important implications regarding the regulation of expression of this gene in normal and malignant tissues. In addition, since a number of other genes with housekeeping promoters also initiate transcription at multiple locations, it is possible that the utilization of multiple promoters may represent a common feature of this class of genes.

Transcriptional regulation of basic fibroblast growth factor gene by p53 in human glioblastoma and hepatocellular carcinoma cells

Mutations of the p53 gene are found in various human cancers. The frequency of its mutation is reported to increase during tumor progression in most tumors. In human gliomas, mutations of the p53 gene are found in about one-third of the malignant forms and in few of the benign ones, indicating their possible involvement in tumor progression. On the other hand, we have recently shown that basic fibroblast growth factor (basic FGF) plays a crucial role in tumor progression as an autocrine growth factor in tissues of human gliomas. Therefore, we hypothesized that p53 might regulate the promoter activity of the basic FGF gene, which has several GC boxes and no typical TATA box. In this study, cotransfection assays using human glioblastoma and hepatocellular carcinoma cells and establishment of stable cell lines expressing mutant-type p53 were performed. The basic FGF gene promoter was demonstrated to be regulated by p53 at the transcriptional level and its basal core promoter was found to be responsive to p53. Expression of endogenous basic FGF was also demonstrated to be activated by mutant type p53. Wild-type p53 repressed gene expression of the basic FGF and its mutant activated it in vitro, implying one of the possible pathways in tumor progression.

Genomic organization, exact localization, and tissue expression of the human CD26 (dipeptidyl peptidase IV) gene

CD26 is a lymphocyte cell surface antigen which is increased during T-cell activation and is also expressed in other tissues. It is an atypical serine protease belonging to the prolyl oligopeptidase family. CD26 has been implicated in a variety of biological functions including T-cell activation, cell-to-cell adhesion, and recently in HIV infection. This paper describes, through the isolation and partial sequencing of eight human CD26 genomic clones, the first information on the genomic organization of the prolyl oligopeptidase family. We have established that the human CD26 gene spans approximately 70 kilobases (kb) and contains 26 exons, ranging in size from 45 base pairs (bp) to 1.4 kb. The nucleotides that encode the serine recognition site (G-W-S-Y-G) are split between two exons. This clearly distinguishes the genomic organization of the prolyl oligopeptidase family from that of the classical serine protease family. The 5' flanking domain of the CD26 gene contains neither a TATA box nor a CAAT box, but a 300 bp region extremely rich in C and G (72%) contains potential binding sites for several transcriptional factors. The human CD26 gene encodes two messages sized at about 4.2 and 2.8 kb. These are both expressed at high levels in the placenta and kidney and at moderate levels in the lung and liver. Only the 4.2 kb mRNA was expressed at low levels in skeletal muscle, heart, brain, and pancreas. Fluorescence in situ hybridization on metaphase chromosome spreads located the human CD26 gene to the long arm of chromosome 2(2q24.3).

Down-regulation of the human c-fos and c-myc proto-oncogene promoters by adeno-associated virus Rep78

Adeno-associated virus (AAV) is a non-pathogenic human parvovirus which has anti-tumor and anti-proliferation properties in tissue culture and animal studies. Furthermore, AAV infection is negatively associated with human cervical cancer. C-myc has been implicated in cervical cancer, and c-fos is involved in signal transduction initiation of cell growth. To study the potential regulation of these two prominent human proto-oncogenes by AAV, the expression of three marker coding sequences ligated 3' of the proto-oncogene promoters were observed. Demonstrated here, the AAV Rep78 gene product was able to down-regulate the human c-fos and c-myc proto-oncogene promoters in all three assay systems. These interactions may partially explain AAVs anti-proliferation properties.

Sequence analysis of the promoter region of the rat somatostatin receptor subtype 1 gene

Somatostatin receptor (SSTR) subtype genes are differentially expressed in brain and various peripheral tissues. RNA blotting and semiquantitative PCR analyses have revealed low levels of SSTR1 mRNA in the gastrointestinal tract and relatively high levels in GH3 anterior pituitary cells. As a first step in the investigation of the regulation of SSTR1 gene expression, we isolated a genomic fragment that contains the promoter region and determined the transcriptional initiation site. The SSTR1 gene lacks introns and TATA and CAAT motifs, but possesses several consensus recognition sequences for the transcription factors GCF and AP-2. The presence, also, of two Pit-1 binding sites could explain the high SSTR1 mRNA levels in GH3 cells.