Gut-enriched Krüppel-like Factor Research Articles

Interaction of Inhibitor of DNA binding 3 (Id3) with Gut-enriched Krüppel-like factor (GKLF) and p53 regulates proliferation of vascular smooth muscle cells

Enhanced proliferation of vascular smooth muscle cells (VSMCs) is one of the key features of the pathogenesis of atherosclerosis. The helix-loop-helix protein Inhibitor of DNA binding 3 (Id3) contributes to regulation of VSMC proliferation in a redox-sensitive manner. We investigated the role of Id3 and its interaction with other redox-sensitive genes, the transcription factor Gut-enriched Krüppel-like factor (GKLF, KLF4) and the tumor suppressor gene p53 in the regulation of VSMC proliferation. Cultured rat aortic VSMCs were transfected with Id3 sense and antisense constructs. Overexpression of Id3 significantly enhanced VSMC proliferation. Id3 antisense transfection inhibited VSMC proliferation induced by the physiological stimuli insulin and platelet-derived growth factor (PDGF). Because p53 is essential for the regulation of proliferation processes, the effect of Id3 on p53 expression was investigated. Id3 overexpression led to decreased p53 protein expression. Co-transfection of p53 sense constructs inhibited the enhanced VSMC mitogenicity induced by Id3 sense transfection. GKLF overexpression, which causes growth arrest in VSMCs, reduced Id3 promoter activity and led to decreased Id3 expression. Id3-induced VSMC proliferation was abolished by GKLF sense co-transfection. Finally, strong Id3 expression was found in the neointima of human coronary artery atherosclerotic plaques but not in healthy coronary arteries. These findings reveal a relevant interaction of GKLF, Id3, and p53 for VSMC proliferation which might constitute a general mechanism of growth control in vascular cells.

Gut-Enriched Krüppel-Like Factor Interaction with Smad3 Inhibits Myofibroblast Differentiation

Gut-enriched Krüppel-like factor (GKLF) has been reported to partially inhibit alpha-smooth muscle actin (alpha-SMA) gene transcription by competing for binding to the TGF-beta control element (TCE) with known activators such as Sp1 and other Krüppel-like factors. This incomplete inhibition via the TCE suggests an additional mechanism, which was evaluated in this study. The results showed that an alpha-SMA promoter mutated in the TCE remained susceptible to inhibition by GKLF in rat lung fibroblasts consistent with the existence of an additional TCE-independent mechanism. Since TGF-beta- induced alpha-SMA expression is Smad3-dependent, potential interaction between GKLF and Smad3 was examined as a basis for this additional inhibitory mechanism. Co-immunoprecipitation and yeast two-hybrid assays revealed that GKLF could bind Smad3 through the Smad3 MH2 domain. Electrophoretic mobility shift assays and ChIP assay indicated that this GKLF-Smad3 interaction inhibited Smad3 binding to the Smad3-binding element (SBE) in the alpha-SMA promoter, and the activity of an SBE containing artificial promoter. Further analysis using smad3(-/-) fibroblasts confirmed that the TCE-independent inhibition by GKLF was dependent on Smad3. These data taken together suggest that in addition to inhibition via the TCE, GKLF represses alpha-SMA gene expression by interacting with Smad3 to prevent Smad3 binding to the SBE. It represents the first evidence to directly link GKLF with Smad3, a key intracellular mediator of TGF-beta signaling, which should lead to a clearer understanding of the mechanism of how GKLF regulates TGF-beta-induced gene expression.

Transcriptional regulation of A33 antigen expression by gut-enriched Krüppel-like factor.

A33 antigen is a membrane-bound protein that is expressed only in intestinal epithelium and in most human colon cancers. Thus, A33 antigen has been explored as a potential therapeutic target for the treatment of colon cancers. However, little is known about the mechanism responsible for the tissue-specific pattern of its expression. In this report, we demonstrate that gut-enriched Krüppel-like factor (GKLF) binds to the promoter region of A33 antigen gene in colonic carcinoma cells and that mutations in the GKLF binding sequence in this region lead to diminished expression of A33 antigen. In addition, the expression of GKLF is linked to the expression of A33 antigen and blocking the expression of GKLF leads to the abolishment of A33 antigen expression. These results suggest that GKLF is a critical regulator in inducing the expression of A33 antigen in intestinal epithelium. While it has been suggested that GKLF is a regulator in inducing cell growth arrest and differentiation of the intestine, our observation that A33 antigen gene is a downstream target for GKLF suggests a more complex and diverse role for GKLF in the gut.

Gut-enriched Krüppel-like factor regulates colonic cell growth through APC/β-catenin pathway

Studies on colorectal carcinogenesis have suggested a critical role of the adenomatous polyposis coli ( APC) gene in the development of colorectal cancer. Gut-enriched Krüppel-like factor (GKLF) is a zinc-finger transcription protein with high expression in the colonic epithelium. Our previous studies have shown that GKLF transcript was significantly decreased in colon cancer tissue and suggested that it might play a role in the tumorigenesis of the colon. The signaling pathway of GKLF-regulated cell growth is currently unknown. We sought to determine if the functions of GKLF are mediated through the APC/β-catenin pathway. In a colon cancer cell line (HT29-APC), containing a zinc-inducible APC gene, GKLF mRNA levels were significantly increased when wild-type APC protein was induced. No effect on GKLF mRNA concentration was observed in a control cell line (HT29-β-gal), containing an analogous inducible lacZ gene. GKLF promoter activity was induced by co-transfection with wild-type APC DNA, suggesting that APC might be involved in transcriptional activation of the GKLF gene. In HT-29 cells, overexpression of GKLF resulted in decreases in β-catenin protein and mRNA levels and down-regulation of GKLF expression led to increase in β-catenin concentration. Overexpression of GKLF in HT-29 cells inhibited DNA synthesis and this effect was attenuated by co-transfection with wild-type β-catenin, suggesting an essential role of β-catenin in GKLF signaling. Furthermore, co-transfection of GKLF in colon cancer SW 480 cells abrogated the transcriptional activity of a β-catenin-T-cell factor (Tcf) reporter construct in a dose-dependent manner. These findings indicate that the growth-suppressive effect of GKLF may be mediated through the APC/β-catenin pathway. We speculate that when APC is mutated, GKLF gene expression is down-regulated, resulting in increases in β-catenin level and transactivation of growth-promoted genes.

Upregulation of transcription factors in lung in the early phase of postpneumonectomy lung growth.

In the adult rodent, pneumonectomy results in compensatory lung growth characterized by cell proliferation. The molecular mechanisms governing this response remain unknown. We hypothesized that, in the early period postpneumonectomy, upregulated expression of transcription factors drives the growth process. We utilized a cDNA expression array to screen for upregulated transcription factors after left pneumonectomy in adult C57BL/6 mice, using unoperated mice as controls. Quantification of mRNA expression in the remaining lung at 2 h demonstrated a twofold or greater upregulation of six transcription factors: early growth response gene-1 (Egr-1), Nurr77, tristetraprolin, the primary inhibitor of nuclear factor-kappa B (I kappa B-alpha), gut-enriched Krüppel-like factor (GKLF), and LRG-21. Northern analysis was used to quantify the upregulation of expression of these genes relative to sham thoracotomy and unoperated controls. The largest increase was in Egr-1 (4.7-fold > naive). Time-course analysis over the first 24 h confirmed the transient nature of the early upregulation. In the context that postpneumonectomy lung growth is associated with cell proliferation and that genes such as Egr-1, Nurr77, LRG-21, and tristetraprolin have known roles in stress response, vascular biology, embryology, and cellular development, these data support the concept that transcription factors function early in the cascade of events leading to the compensatory response.

A Nucleus-Localization-Deficient Mutant Serves as a Dominant-Negative Inhibitor of Gut-Enriched Krüppel-like Factor Function

Cancer cells differ from normal cells in many aspects, including loss of differentiation and uninhibited cell proliferation. Recent studies have suggested that gut-enriched Krüppel-like factor (GKLF) played an important role in the regulation of cell growth in the colon. Studies from this laboratory have shown that GKLF protein predominantly expressed in the cytoplasm but not the nucleus of colon cancer cells, suggesting that impaired nuclear translocation of GKLF might contribute to cancer formation. In this report, a region containing putative nuclear localization signal (NLS) of GKLF (PKRGRR; amino acids 385–390) was investigated. Mutation of KR to WT had no effect on the inhibitory properties of GKLF on cyclin D1 promoter activity and [3H]thymidine uptake in HT-29 cells, whereas mutation of RR to GL abolished GKLF function completely. Additional mutation analyses demonstrated that Arg390 is the most critical moiety within this region that mediated GKLF function and its nucleus localization. Cotransfection of Arg390 mutant (RR/RS) completely inhibited wild-type GKLF function, and GFP-RR/RS GKLF fusion proteins failed to translocate to the nucleus. The results from this study demonstrate that Arg390 confers the NLS of GKLF and that the nucleus-localization-deficient mutant serves as dominant-negative inhibitor of GKLF function.

Positive- and Negative-acting Krüppel-like Transcription Factors Bind a Transforming Growth Factor β Control Element Required for Expression of the Smooth Muscle Cell Differentiation Marker SM22α in Vivo

Transforming growth factor beta (TGF-beta) is implicated in the regulation of smooth muscle cell (SMC) differentiation. We previously identified a novel TGF-beta control element (TCE) in the promoters of SMC differentiation marker genes, including alpha-smooth muscle actin and SM22alpha. In this study, the importance of the TCE in regulation of SM22alpha gene expression in vivo was investigated by mutating it within the context of a mouse SM22alpha promoter-lacZ transgenic construct. Mutation of the TCE completely abolished SM22alpha promoter activity in arterial SMCs as well as in developing heart and skeletal muscle. To identify the transcription factor(s) binding to the TCE, we performed yeast one-hybrid cloning analysis and identified gut-enriched Krüppel-like factor (GKLF). However, cotransfection studies in cultured cells showed that GKLF repressed the TGF-beta-dependent increases in SM22alpha and alpha-smooth muscle actin promoter activities. Furthermore, GKLF was not highly expressed in differentiated SMCs in vivo, and TGF-beta down-regulated GKLF expression in dedifferentiated cultured SMCs. In contrast, overexpression of a related factor (BTEB2) transactivated SM22alpha promoter activity. Thus, our findings suggest a reciprocal role for related Krüppel-like transcription factors in the regulation of SMC differentiation through a TCE-dependent mechanism.

Role of gut-enriched Krüppel-like factor in colonic cell growth and differentiation.

Cancer cells differ from normal cells in many aspects, including hyperproliferation and loss of differentiation. Recent research has focused on the role of transcription factors in regulating abnormal cell growth. Gut-enriched Krüppel-like factor (GKLF) is a newly identified eukaryotic zinc finger protein expressed extensively in the gastrointestinal tract. In the current study, we demonstrated that GKLF mRNA levels were significantly decreased in the dysplastic epithelium of the colon, including adenomatous polyp and cancer. GKLF immunostains in the normal colon were higher at the surface epithelium and gradually decreased toward the crypt, but this gradient was not present in the adenomatous and cancerous mucosa. Constitutive overexpression of GKLF DNA in a human colonic adenocarcinoma cell line (HT-29) decreased [(3)H]thymidine incorporation, whereas suppression of GKLF gene increased DNA synthesis, indicating that downregulation of the GKLF gene might contribute to cellular hyperproliferation. Cyclin D1 (CD1) protein level and CD1-associated kinase activity were decreased in HT-29 cell overexpressed GKLF cDNA, and CD1 promoter activity was profoundly suppressed by GKLF. When HT-29 cells were cultured in the presence of sodium butyrate, GKLF mRNA levels increased as cells acquired more differentiated phenotypes. These results suggest that GKLF plays an important role in regulating cell growth and differentiation in the colonic epithelium and that downregulation of GKLF expression may cause colonic cells to become hyperproliferative. Furthermore, GKLF appears to be a transcriptional repressor of the CD1 gene.

Up-regulation of gut-enriched krüppel-like factor by interferon-γ in human colon carcinoma cells

Interferon-γ (IFN-γ) induces growth arrest and apoptosis of tumor cells but the mechanisms for these functions are unknown. Recently, gut-enriched krüppel-like factor (GKLF) was found to possess similar biological properties. Treatment of HT-29 cells with IFN-γ inhibited cell proliferation and induced apoptosis, the effect was found to associate with GKLF expression. IFN-γ stimulates GKLF mRNA and protein levels in a dose- and time-dependent manner and this process is independent of p53, occurs rapidly and does not require de novo protein synthesis indicating that GKLF is an immediate-early IFN-γ-responsive gene. Moreover, overexpression of GKLF results in similar effect as IFN-γ suggesting that GKLF may function as a downstream target of IFN-γ.

Decreased expression of the gut-enriched Krüppel-like factor gene in intestinal adenomas of multiple intestinal neoplasia mice and in colonic adenomas of familial adenomatous polyposis patients

Gut-enriched Krüppel-like factor (GKLF) is a zinc finger-containing transcription factor, the expression of which is associated with growth arrest. We compared Gklf expression in intestinal and colonic adenomas to normal mucosa in multiple intestinal neoplasia ( Min) mice and familial adenomatous polyposis (FAP) patients, respectively, using semi-quantitative RT-PCR. In Min mice, the level of Gklf transcript is highest in normal-appearing intestinal tissues and decreases as the size of the adenoma increases. In FAP patients, the level of GKLF transcript is lower in adenomas compared to paired normal-appearing mucosa from the same patient or normal colonic mucosa from control individuals without FAP. The possibility of DNA methylation as a cause for the decreased expression of Gklf in adenomas of Min mice was investigated by methylation-specific PCR. Results indicate that the Gklf gene is not methylated in either normal or tumorous tissues. The findings of our study are therefore consistent with the potential role of GKLF as a negative growth regulator of gut epithelial cells.

GKLF in thymus epithelium as a developmentally regulated element of thymocyte-stroma cross-talk

Gut-enriched Krüppel-like factor (GKLF) is a transcriptional regulator expressed in differentiated epithelia. We identified GKLF transcript as a regulated element in thymic epithelium of recombinase-deficient mice during thymus development induced by anti-CD3 antibody injection. This treatment recapitulates the organogenetic process depending on productive rearrangement of T cell receptor (TCR) β gene with thymocytes expansion and acquisition of the CD4 +8 + double positive phenotype. In wildtype mice, GKLF is expressed very early in embryogenesis and becomes intensely up-regulated in thymus epithelium at day 18 of gestation when TCR β expressing cells have selectively expanded and express both CD4 and CD8. The results presented here suggest that thymocytes may regulate GKLF transcriptionally in the cortical epithelium at the developmental check-point controlled by TCR β gene rearrangement. Furthermore, GKLF expression in hematopoietic stroma might suggest the thus far uncharacterised participation of this factor in hematopoiesis.

The Gut-enriched Krüppel-like Factor Suppresses the Activity of the CYP1A1 Promoter in an Sp1-dependent Fashion

The gut-enriched Krüppel-like factor (GKLF) is a newly identified zinc finger-containing transcription factor. Recent studies indicate that GKLF binds to a core DNA sequence of 5'-(G/A)(G/A)GG(C/T)G(C/T)-3', which is found in an endogenous cis element, the basic transcription element (BTE) of the cytochrome P-450IA1 (CYP1A1) promoter. The present study characterizes the ability of GKLF to regulate CYP1A1 expression. By electrophoretic mobility gel shift assay (EMSA) and methylation interference assay, GKLF was found to bind BTE in a manner similar to several other transcription factors known to interact with BTE including Sp1 and BTEB. Cotransfection studies in Chinese hamster ovary cells showed that GKLF inhibited the CYP1A1 promoter in a dose- and BTE-dependent manner. The same experiments also revealed that BTE was responsible for a significant portion of the CYP1A1 promoter activity. EMSA of nuclear extracts from Chinese hamster ovary cells showed that Sp1 and Sp3 were two major proteins that interacted with BTE. Additional cotransfection studies showed that GKLF inhibited Sp1-mediated activation of the CYP1A1 promoter. In contrast, GKLF enhanced Sp3-dependent suppression of the same promoter. Moreover, the ability of GKLF to inhibit Sp1-dependent transactivation was in part due to physical interaction of the two proteins. These findings indicate that GKLF is a negative regulator of the CYP1A1 promoter in a BTE-dependent fashion and that this inhibitory effect is in part mediated by physical interaction with Sp1.

The gut-enriched Krüppel-like factor (GKLF) suppresses the promoter activity of the cytochrome P450 1A1 (CYP1A1) gene in a SP1-dependent fashion

Background: GKLF is a recently identified transcription factor that contains 3 C2H 2 zinc fingers with homology to the Drosophila Kriippel protein [Shields, Christy and Yang (1996) J. Biol. Chem. 271, 20009; Shields and Yang (1997) J. Biol. Chem. 277~2 18504]. Expression of GKLF is enriched in the gut epithelium and is associated with growth arrest. Recent studies have identified a consensus DNA sequence to which GKLF binds [Shields and Yang (1998) Nucl. Acids Res., in press]. This sequence is very similar to the basal transcription dement (BTE) this is essential for the promoter activity of many genes in the cytochrome P450 family, including CYP1A1. Aim: The aim of the present study is to investigate whether GKLF is involved in the regulation of the CYP1A1 promoter through the BTE. Methods: The binding of GKLF to BTE was analyzed by methylation interference and electrophoretic mobility shift assays (EMSA) using partially purified recombinant GKLF and a radioactively labeled double-stranded oligonucleotide containing the GKLF consensus binding sequence (named TDA) or BTE. The effect of GKLF on CYP1A1 promoter activity was examined by cotransfection experiments in Chinese hamster ovary (CHO) cells with an eukaryotic expression construct containing full-length or truncated GKLF and a chloramphenicol acetyl transferase (CAT) reporter gene driven by the CYP1A1 Y-flanking sequence including or not BTE. Results: EMSA of labeled TDA and BTE using recombinant GKLF demonstrated the formation of a single, identical DNA-protein complex. The minimal essential DNA sequences within TDA and BTE that bound GKLF were identical as defined by base-specific mutagenesis and methylation interference assays. In transiently transfected CHO cells, an expression construct containing full-length but not truncated GKLF was able to suppress, in a dose-dependent fashion, the activity of the CAT reporter driven by the wild-type CYP1A1 promoter but not by a mutated promoter in which the BTE was specifically deleted. As a deletion of the BTE from the CYP1A1 promoter also resulted in a significant decrease in the basal promoter activity, nuclear extracts from CHO cells were prepared and analyzed by EMSA. The results indicate that the primary protein in CHO cells binding to BTE was Spl as demonstrated by antibody super-shift experiments. Cotransfection of the CYP1A1 promoter-reporters with an expression construct containing Spl showed that Spl transactivated the CYP1A1 promoter in a BTE-dependent fashion. The further addition of GKLF to the above transfection condition resulted in a dose-dependent abrogation of the ability of Spl to activate CYP1A1 promoter. Conclusion: The results indicate that GKLF is an GASTROENTEROLOGY Vol. 114, No. 4

Transactivation of the Human Keratin 4 and Epstein-Barr Virus ED-L2 Promoters by Gut-enriched Krüppel-like Factor

The Krüppel-like family of transcription factors comprises genes that appear to have tissue-restricted functions. Expression of gut-enriched Krüppel-like factor (GKLF) may be important in the switch from proliferation to differentiation in the squamous epithelium. We sought to determine transcriptionally mediated effects of GKLF on two promoters active in the esophageal squamous epithelium, namely the Epstein-Barr virus ED-L2 and human keratin 4 promoters. Both promoters contain a CACCC-like motif previously shown to bind GKLF. To determine whether GKLF regulates genes containing this element, we first demonstrated expression and then cloned the full-length human GKLF from an esophageal squamous carcinoma cell line. In a transient transfection system, GKLF increased the activity of both promoters >25-fold, localized to regions containing the CACCC-like element. Recombinant GKLF specifically binds the CACCC-like motif in both promoters. GKLF epitope-tagged protein leads to the formation of two proteins of 65 and 34 kDa. The chromatographically purified 65-kDa protein binds the CACCC-like element from both Epstein-Barr virus ED-L2 and keratin 4 promoters, which is not attenuated by the 34-kDa protein. In summary, GKLF is expressed in esophageal squamous epithelial cells and transcriptionally activates two esophageal epithelial promoters important at the transition toward differentiation.

Transactivation by the gut-enriched Krüppel-like factor (GKLF) depends on acidic amino acid residues and on protein-protein interaction

Transactivation by the gut-enriched Krüppel-like factor (GKLF) depends on acidic amino acid residues and on protein-protein interaction

Identification of the DNA sequence that interacts with the gut-enriched Krüppel-like factor.

The gut-enriched Krüppel-like factor (GKLF) is a recently identified eukaryotic transcription factor that contains three C2H2zinc fingers. The amino acid sequence of the zinc finger portion of GKLF is closely related to several Krüppel proteins, including the lung Krüppel-like factor (LKLF), the erythroid Krüppel-like factor (EKLF) and the basic transcription element binding protein 2 (BTEB2). The DNA sequence to which GKLF binds has not been definitively established. In the present study we determined the DNA binding sequence of GKLF using highly purified recombinant GKLF in a target detection assay of an oligonucleotide library consisting of random sequences. Upon repeated rounds of selection and subsequent characterization of the selected sequences by base-specific mutagenesis a DNA with the sequence 5'-G/AG/AGGC/TGC/T-3' was found to contain the minimal essential binding site for GKLF. This sequence is present in the promoters of two previously characterized genes: the CACCC element of the beta-globin gene, which interacts with EKLF, and the basic transcription element (BTE) of the CYP1A1 gene, which interacts with Sp1 and several Sp1-like transcription factors. Moreover, the selected GKLF binding sequence was capable of mediating transactivation of a linked reporter gene by GKLF in co-transfection experiments. Our results establish GKLF as a sequence-specific transcription factor likely involved in regulation of expression of endogenous genes.

Expression of the gut-enriched Krüppel-like factor gene during development and intestinal tumorigenesis

We examined the expression of GKLF (gut-enriched Krüppel-like factor), a recently identified zinc finger-containing transcription factor, in mice during development using the ribonuclease protection assay. In the adult, the level of GKLF transcript is abundant throughout the gastrointestinal tract. Between embryonic days 10 and 19 (E10 and E19) of development, the initial level of whole embryo GKLF transcript is low but begins to rise on E13 and peaks on E17. In the newborn, GKLF transcript level is higher in the colon than in the small intestine although the levels in both organs rise with increasing age. Expression of GKLF was also examined in the intestinal tract of the Min mouse, a model of intestinal tumorigenesis. The level of GKLF transcript is significantly decreased in the intestine of Min mice during a period of tumor formation when compared to age-matched control littermates. Our findings indicate that GKLF expression correlates with certain periods of gut development and is down-regulated during intestinal tumorigenesis, suggesting that GKLF may play a role in gut development and/or tumor formation.

Two potent nuclear localization signals in the gut-enriched Krüppel-like factor define a subfamily of closely related Krüppel proteins.

The gut-enriched Krüppel-like factor (GKLF) is a newly identified transcription factor that contains three C2H2 Krüppel-type zinc fingers. Previous immunocytochemical studies indicate that GKLF is exclusively localized to the nucleus. To identify the nuclear localization signal (NLS) within GKLF, cDNA constructs with various deletions in the coding region of GKLF were generated and analyzed by indirect immunofluorescence in transfected COS-1 cells. In addition, constructs fusing regions representing putative NLSs of GKLF to green fluorescent protein (GFP) were generated and examined by fluorescence microscopy in similarly transfected cells. The results indicate that GKLF contains two potent, independent NLSs: one within the zinc fingers and the other in a cluster of basic amino acids (called 5' basic region) immediately preceding the first zinc finger. In comparison, putative NLSs within the zinc fingers and the 5' basic region of a related Krüppel protein, zif268/Egr-1, are relatively less efficient in their ability to translocate GFP into the nucleus. A search in the protein sequence data base revealed that despite the existence of numerous Krüppel proteins, only two, the lung Krüppel-like factor (LKLF) and the erythroid Krüppel-like factor (EKLF), exhibit similar NLSs to those of GKLF. These findings indicate that GKLF, LKLF, and EKLF are members of a subfamily of closely related Krüppel proteins.

Identification and Characterization of a Gene Encoding a Gut-enriched Krüppel-like Factor Expressed during Growth Arrest

A cDNA clone, named gut-enriched Krüppel-like factor (GKLF), was isolated from an NIH 3T3 library using a probe encoding the zinc finger region of the immediate-early transcription factor zif/268. The deduced GKLF amino acid sequence contains three tandem zinc fingers that are related to members of the Krüppel family of transcription factors. By indirect immunofluorescence, GKLF is localized to the cell nucleus. In cultured fibroblasts, GKLF mRNA is found in high levels in growth-arrested cells and is nearly undetectable in cells that are in the exponential phase of proliferation. The growth-arresting nature of GKLF is demonstrated by an inhibition of DNA synthesis in cells transfected with a GKLF-expressing plasmid construct. In the mouse, GKLF mRNA is present in select tissues and is most abundant in the colon, followed by the testis, lung, and small intestine. In situ hybridization experiments indicate that GKLF mRNA is enriched in epithelial cells located in the middle to upper crypt region of the colonic mucosa. Taken together, these results suggest that GKLF is potentially a negative regulator of cell growth in tissues such as the gut mucosa, where cell proliferation is intimately coupled to growth arrest and differentiation.

Identification and characterization of a zinc finger-containing, gut-enriched Krüppel-like factor (GKLF) gene expressed in G 0 restricted cells : [formula omitted], RJ Christy, and VW Yang. Depts. of Med. and Biol. Chem., The Johns Hopkins Univ. Sch. of Med., Baltimore, MD. and Center for Mol. Med., Inst. of Biotechnology, Univ. of Texas Health Sci. Center, San Antonio, TX

Identification and characterization of a zinc finger-containing, gut-enriched Krüppel-like factor (GKLF) gene expressed in G 0 restricted cells : [formula omitted], RJ Christy, and VW Yang. Depts. of Med. and Biol. Chem., The Johns Hopkins Univ. Sch. of Med., Baltimore, MD. and Center for Mol. Med., Inst. of Biotechnology, Univ. of Texas Health Sci. Center, San Antonio, TX