Kruppel-like factors regulate the Lama1 gene encoding the laminin alpha1 chain

RNA-dependent Amplification of Mammalian mRNA Encoding Extracellullar Matrix Proteins: Identification of Chimeric RNA Intermediates for α1, β1, and γ1 Chains of Laminin

De novo production of RNA on RNA template, a process known as RNA-dependent RNA synthesis, RdRs, and the enzymatic activity conducting it, RNA-dependent RNA polymerase, RdRp, were initially considered to be exclusively virus-specific. Eventually, however, the occurrence of RdRs and the ubiquitous presence of conventional RdRp were demonstrated in numerous eukaryotic organisms. The evidence that the enzymatic machinery capable of RdRs is present in mammalian cells was derived from studies of viruses, such as hepatitis delta virus, HDV, that do not encode RdRp yet undergo a robust RNA replication once inside the mammalian host; thus firmly establishing its occurrence and functionality. Moreover, it became clear that RdRp activity, apparently in a non-conventional form, is constitutively present in most, if not in all, mammalian cells. Because such activity was shown to produce short transcripts, given its apparent involvement in RNA interference phenomena, and because double-stranded RNA is known to trigger cellular responses leading to its degradation, it was generally assumed that its role in mammalian cells is restricted to a regulatory function. However, at the same time, an enzymatic activity capable of generating complete antisense RNA complements of mRNAs was discovered in mammalian cells undergoing terminal differentiation. Moreover, observations of widespread synthesis of antisense RNAs initiating at the 3'poly(A) of mRNAs in human cells suggested an extensive cellular utilization of mammalian RdRp. These results led to the development of a model of RdRp-facilitated and antisense RNA-mediated amplification of mammalian mRNA. Recent detection of the major model-predicted identifiers, chimeric RNA intermediates containing both sense and antisense RNA strands covalently joined in a rigorously predicted and uniquely defined manner, as well as the identification of a putative chimeric RNA end product of this process, validated the proposed model. The results corroborating mammalian RNA-dependent mRNA amplification were obtained in vivo with cells undergoing terminal erythroid differentiation and programmed for only a short survival span. This raises a question of whether mammalian RNA-dependent mRNA amplification is a specialized occurrence limited to extreme circumstances of terminal differentiation or a general physiological phenomenon. The present study addresses this question by testing for the occurrence of RNA-dependent amplification of mRNA encoding extracellular matrix proteins abundantly produced throughout the tissue and organ development and homeostasis, an exceptionally revealing indicator of the range and scope of this phenomenon. We report here the detection of major identifiers of RNA-dependent amplification of mRNA encoding α1, β1, and γ1 chains of laminin in mouse tissues producing large quantities of extracellular matrix proteins. The results obtained warrant reinterpretation of the mechanisms involved in ubiquitous and abundant production and deposition of extracellular matrix proteins, confirm the occurrence of mammalian RNA-dependent mRNA amplification as a new mode of genomic protein-encoding information transfer, and establish it as a general physiological phenomenon.

News from Mars: Two-Tier Paradox, Intracellular PCR, Chimeric Junction Shift, Dark Matter mRNA and Other Remarkable Features of Mammalian RNA-Dependent mRNA Amplification. Implications for Alzheimer's Disease, RNA-Based Vaccines and mRNA Therapeutics

Molecular Biology, a branch of science established to examine the flow of information from "letters" encrypted into DNA structure to functional proteins, was initially defined by a concept of DNA-to-RNA-to-Protein information movement, a notion termed the Central Dogma of Molecular Biology. RNA-dependent mRNA amplification, a novel mode of eukaryotic protein-encoding RNA-to-RNA-to-Protein genomic information transfer, constitutes the extension of the Central Dogma in the context of mammalian cells. It was shown to occur in cellular circumstances requiring exceptionally high levels of production of specific polypeptides, e.g. globin chains during erythroid differentiation or defined secreted proteins in the context of extracellular matrix deposition. Its potency is reflected in the observed cellular levels of the resulting amplified mRNA product: At the peak of the erythroid differentiation, for example, the amount of globin mRNA produced in the amplification pathway is about 1500-fold higher than the amount of its conventionally generated counterpart in the same cells. The cellular enzymatic machinery at the core of this process, RNA-dependent RNA polymerase activity (RdRp), albeit in a non-conventional form, was shown to be constitutively and ubiquitously present, and RNA-dependent RNA synthesis (RdRs) appeared to regularly occur, in mammalian cells. Under most circumstances, the mammalian RdRp activity produces only short antisense RNA transcripts. Generation of complete antisense RNA transcripts and amplification of mRNA molecules require the activation of inducible components of the mammalian RdRp complex. The mechanism of such activation is not clear. The present article suggests that it is triggered by a variety of cellular stresses and occurs in the context of stress responses in general and within the framework of the integrated stress response (ISR) in particular. In this process, various cellular stresses activate, in a stress type-specific manner, defined members of the mammalian translation initiation factor 2α, eIF2α, kinase family: PKR, GCN2, PERK and HRI. Any of these kinases, in an activated form, phosphorylates eIF2α. This results in suppression of global cellular protein synthesis but also in activation of expression of select group of transcription factors including ATF4, ATF5 and CHOP. These transcription factors either function as inducible components of the RdRp complex or enable their expression. The assembly of the competent RdRp complex activates mammalian RNA-dependent mRNA amplification, which appears to be a two-tier process. Tier One is a "chimeric" pathway, named so because it results in an amplified chimeric mRNA molecule containing a fragment of the antisense RNA strand at its 5' terminus. Tier Two further amplifies one of the two RNA end products of the chimeric pathway and constitutes the physiologically occurring intracellular polymerase chain reaction, iPCR. Depending on the structure of the initial mRNA amplification progenitor, the chimeric pathway, Tier One, may result in multiple outcomes including chimeric mRNA that produces either a polypeptide identical to the original, conventional mRNA progenitor-encoded protein or only its C-terminal fragment, CTF. The chimeric RNA end product of Tier One may also produce a polypeptide that is non-contiguously encoded in the genome, activate translation from an open reading frame, which is "silent" in a conventionally transcribed mRNA, or initiate an abortive translation. In sharp contrast, regardless of the outcome of Tier One, the mRNA end product of Tier Two of mammalian mRNA amplification, the iPCR pathway, always produces a polypeptide identical to a conventional mRNA progenitor-encoded protein. This discordance is referred to as the Two-Tier Paradox and discussed in detail in the present article. On the other hand, both Tiers are similar in that they result in heavily modified mRNA molecules resistant to reverse transcription, undetectable by reverse transcription-based methods of sequencing and therefore constituting a proverbial "Dark Matter" mRNA, despite being highly ubiquitous. It appears that in addition to their other functions, the modifications of the amplified mRNA render it compatible, unlike the bulk of cellular mRNA, with phosphorylated eIF2α in translation, implying that in addition to being extraordinarily abundant due to the method of its generation, amplified mRNA is also preferentially translated under the ISR conditions, thus augmenting the efficiency of the amplification process. The vital importance of powerful mechanisms of amplification of protein-encoding genomic information in normal physiology is self-evident. Their malfunctions or misuse appear to be associated with two types of abnormalities, the deficiency of a protein normally produced by these mechanisms and the mRNA amplification-mediated overproduction of a protein normally not generated by such a process. Certain classes of beta-thalassemia exemplify the first type, whereas the second type is represented by overproduction of beta-amyloid in Alzheimer's disease. Moreover, the proposed mechanism of Alzheimer's disease allows a crucial and verifiable prediction, namely that the disease-causing intraneuronally retained variant of beta-amyloid differs from that produced conventionally by βAPP proteolysis in that it contains the additional methionine or acetylated methionine at its N-terminus. Because of its extraordinary evidential value as a natural reporter of the mRNA amplification pathway, this feature, if proven, would, arguably, constitute the proverbial Holy Grail not only for Alzheimer's disease but also for the mammalian RNA-dependent mRNA amplification field in general. Both examples are discussed in detail in the present article, which summarizes and systematizes our current understanding of the field and describes two categories of reporter constructs, one for the chimeric Tier of mRNA amplification, another for the iPCR pathway; both reporter types are essential for elucidating underlying molecular mechanisms. It also suggests, in light of the recently demonstrated feasibility of RNA-based vaccines, that the targeted intracellular amplification of exogenously introduced amplification-eligible antigen-encoding mRNAs via the induced or naturally occurring RNA-dependent mRNA amplification pathway could be of substantial benefit in triggering a fast and potent immune response and instrumental in the development of future vaccines. Similar approaches can also be effective in achieving efficient and sustained expression of exogenous mRNA in mRNA therapeutics.

Protein-Encoding RNA-to-RNA Information Transfer in Mammalian Cells: Principles of RNA-Dependent mRNA Amplification

The transfer of protein-encoding genetic information from DNA to RNA to protein, a process formalized as the "Central Dogma of Molecular Biology", has undergone a significant evolution since its inception. It was amended to account for the information flow from RNA to DNA, the reverse transcription, and for the information transfer from RNA to RNA, the RNA-dependent RNA synthesis. These processes, both potentially leading to protein production, were initially described only in viral systems, and although RNA-dependent RNA polymerase activity was shown to be present, and RNA-dependent RNA synthesis found to occur, in mammalian cells, its function was presumed to be restricted to regulatory. However, recent results, obtained with multiple mRNA species in several mammalian systems, strongly indicate the occurrence of protein-encoding RNA to RNA information transfer in mammalian cells. It can result in the rapid production of the extraordinary quantities of specific proteins as was seen in cases of terminal cellular differentiation and during cellular deposition of extracellular matrix molecules. A malfunction of this process may be involved in pathologies associated either with the deficiency of a protein normally produced by this mechanism or with the abnormal abundance of a protein or of its C-terminal fragment. It seems to be responsible for some types of familial thalassemia and may underlie the overproduction of beta amyloid in sporadic Alzheimer's disease. The aim of the present article is to systematize the current knowledge and understanding of this pathway. The outlined framework introduces unexpected features of the mRNA amplification such as its ability to generate polypeptides non-contiguously encoded in the genome, its second Tier, a physiologically occurring intracellular polymerase chain reaction, iPCR, a "Two-Tier Paradox" and RNA "Dark Matter". RNA-dependent mRNA amplification represents a new mode of genomic protein-encoding information transfer in mammalian cells. Its potential physiological impact is substantial, it appears relevant to multiple pathologies and its understanding opens new venues of therapeutic interference, it suggests powerful novel bioengineering approaches and its further rigorous investigations are highly warranted.

Characterization of potential driver mutations involved in human breast cancer by computational approaches

Breast cancer is the second most frequently occurring form of cancer and is also the second most lethal cancer in women worldwide. A genetic mutation is one of the key factors that alter multiple cellular regulatory pathways and drive breast cancer initiation and progression yet nature of these cancer drivers remains elusive. In this article, we have reviewed various computational perspectives and algorithms for exploring breast cancer driver mutation genes. Using both frequency based and mutational exclusivity based approaches, we identified 195 driver genes and shortlisted 63 of them as candidate drivers for breast cancer using various computational approaches. Finally, we conducted network and pathway analysis to explore their functions in breast tumorigenesis including tumor initiation, progression, and metastasis.

Cancer astrocytes have a more conserved molecular status in long recurrence free survival (RFS) IDH1 wild-type glioblastoma patients: new emerging cancer players

Glioblastoma is a devastating disease that despite all the information gathered so far, its optimal management remains elusive due to the absence of validated targets from clinical studies. A better clarification of the molecular mechanisms is needed. In this study, having access to IDH1 wild-type glioblastoma of patients with exceptionally long recurrence free survival (RFS), we decided to compare their mutational and gene expression profile to groups of IDH1 wild-type glioblastoma of patients with shorter RFS, by using NGS technology. The exome analysis revealed that Long-RFS tumors have a lower mutational rate compared to the other groups. A total of 158 genes were found differentially expressed among the groups, 112 of which distinguished the two RFS extreme groups. Overall, the exome data suggests that shorter RFS tumors could be, chronologically, in a more advanced state in the muli-step tumor process of sequential accumulation of mutations. New players in this kind of cancer emerge from the analysis, confirmed at the RNA/DNA level, identifying, therefore, possible oncodrivers or tumor suppressor genes.

Laminin α1 reduces muscular dystrophy in dy2J mice

Muscular dystrophies, including laminin α2 chain-deficient muscular dystrophy (LAMA2-CMD), are associated with immense personal, social and economic burdens. Thus, effective treatments are urgently needed. LAMA2-CMD is either a severe, early-onset condition with complete laminin α2 chain-deficiency or a milder, late-onset form with partial laminin α2 chain-deficiency. Mouse models dy^3K/dy^3K and dy^2J/dy^2J, respectively, recapitulate these two forms of LAMA2-CMD very well. We have previously demonstrated that laminin α1 chain significantly reduces muscular dystrophy in laminin α2 chain-deficient dy^3K/dy^3K mice. Among all the different pre-clinical approaches that have been evaluated in mice, laminin α1 chain-mediated therapy has been shown to be one of the most effective lines of attack. However, it has remained unclear if laminin α1 chain-mediated treatment is also applicable for partial laminin α2 chain-deficiency. Hence, we have generated dy^2J/dy^2J mice (that express a substantial amount of an N-terminal truncated laminin α2 chain) overexpressing laminin α1 chain in the neuromuscular system. The laminin α1 chain transgene ameliorated the dystrophic phenotype, restored muscle strength and reduced peripheral neuropathy. Thus, these findings provide additional support for the development of laminin α1 chain-based therapy for LAMA2-CMD.

Involvement of CRF2 signaling in enterocyte differentiation

AIM

To determine the role of corticotropin releasing factor receptor (CRF2) in epithelial permeability and enterocyte cell differentiation.

METHODS

For this purpose, we used rat Sprague Dawley and various colon carcinoma cell lines (SW620, HCT8R, HT-29 and Caco-2 cell lines). Expression of CRF2 protein was analyzed by fluorescent immunolabeling in normal rat colon and then by western blot in dissociated colonic epithelial cells and in the lysates of colon carcinoma cell lines or during the early differentiation of HT-29 cells (ten first days). To assess the impact of CRF2 signaling on colonic cell differentiation, HT-29 and Caco-2 cells were exposed to Urocortin 3 recombinant proteins (Ucn3, 100 nmol/L). In some experiments, cells were pre-exposed to the astressin 2b (A2b) a CRF2 antagonist in order to inhibit the action of Ucn3. Intestinal cell differentiation was first analyzed by functional assays: the trans-cellular permeability and the para-cellular permeability were determined by Dextran-FITC intake and measure of the transepithelial electrical resistance respectively. Morphological modifications associated to epithelial dysfunction were analyzed by confocal microscopy after fluorescent labeling of actin (phaloidin-TRITC) and intercellular adhesion proteins such as E-cadherin, p120ctn, occludin and ZO-1. The establishment of mature adherens junctions (AJ) was monitored by following the distribution of AJ proteins in lipid raft fractions, after separation of cell lysates on sucrose gradients. Finally, the mRNA and the protein expression levels of characteristic markers of intestinal epithelial cell (IEC) differentiation such as the transcriptional factor krüppel-like factor 4 (KLF4) or the dipeptidyl peptidase IV (DPPIV) were performed by RT-PCR and western blot respectively. The specific activities of DPPIV and alkaline phosphatase (AP) enzymes were determined by a colorimetric method.

RESULTS

CRF2 protein is preferentially expressed in undifferentiated epithelial cells from the crypts of colon and in human colon carcinoma cell lines. Furthermore, CRF2 expression is down regulated according to the kinetic of HT-29 cell differentiation. By performing functional assays, we found that Ucn3-induced CRF2 signaling alters both para- and trans-cellular permeability of differentiated HT-29 and Caco-2 cells. These effects are partly mediated by Ucn3-induced morphological changes associated with the disruption of mature AJ in HT-29 cells and tight junctions (TJ) in Caco-2 cells. Ucn3-mediated activation of CRF2 decreases mRNA and protein expression levels of KLF4 a transcription factor involved in IEC differentiation. This signaling is correlated to a down-regulation of key IEC markers such as DPPIV and AP, at both transcriptional and post-transcriptional levels.

CONCLUSION

Our findings suggest that CRF2 signaling could modulate IEC differentiation. These mechanisms could be relevant to the stress induced epithelial alterations found in inflammatory bowel diseases.

Increased Expression of Laminin Subunit Alpha 1 Chain by dCas9-VP160

Laminin-111 protein complex links the extracellular matrix to integrin α7β1 in sarcolemma, thus replacing in dystrophic muscles links normally insured by the dystrophin complex. Laminin-111 injection in mdx mouse stabilized sarcolemma, restored serum creatine kinase to wild-type levels, and protected muscles from exercised-induced damages. These results suggested that increased laminin-111 is a potential therapy for DMD. Laminin subunit beta 1 and laminin subunit gamma 1 are expressed in adult human muscle, but laminin subunit alpha 1 (LAMA1) gene is expressed only during embryogenesis. We thus developed an alternative method to laminin-111 protein repeated administration by inducing expression of the endogenous mouse Lama1 gene. This was done with the CRSPR/Cas9 system, i.e., by targeting the Lama1 promoter with one or several gRNAs and a dCas9 coupled with the VP160 transcription activation domain. Lama1 mRNA (qRT-PCR) and proteins (immunohistochemistry and western blot) were not detected in the control C2C12 myoblasts and in control muscles. However, significant expression was observed in cells transfected and in mouse muscles electroporated with plasmids coding for dCas9-VP160 and a gRNA. Larger synergic increases were observed by using two or three gRNAs. The increased Lama1 expression did not modify the expression of the α7 and β1 integrins. Increased expression of Lama1 by the CRISPR/Cas9 system will have to be further investigated by systemic delivery of the CRISPR/Cas9 components to verify whether this could be a treatment for several myopathies.

Hedgehog signalling acts upstream of Laminin alpha1 transcription in the zebrafish paraxial mesoderm

Laminin-111 (α1β1γ1) is a member of the Laminin family of extra-cellular matrix proteins that comprises 16 members, components of basement membranes. Laminin-111, one of the first Laminin proteins synthesised during embryogenesis, is required for basement membrane deposition and has essential roles in tissue morphogenesis and patterning. Yet, the mechanisms controlling Laminin-111 expression are poorly understood. We generated a zebrafish transgenic reporter line that reproduces faithfully the expression pattern of lama1, the gene encoding Laminin α1, and we used this reporter line to investigate lama1 transcriptional regulation. Our findings established that lama1 expression is controlled by intronic enhancers, including an enhancer directing expression in the paraxial mesoderm, anterior spinal cord and hindbrain, located in intron 1. We show that Hedgehog signalling is necessary and sufficient for lama1 transcription in the paraxial mesoderm and identify putative Gli/Zic binding sites that may mediate this control. These findings uncover a conserved role for Hedgehog signalling in the control of basement membrane assembly via its transcriptional regulation of lama1, and provide a mechanism to coordinate muscle cell fate specification in the zebrafish embryo.

Expression Data Analysis for the Identification of Potential Biomarker of Pregnancy Associated Breast Cancer

Breast cancer affects every 1 of 3000 pregnant women or in the first post-partum year is referred as Pregnancy Associated Breast Cancer (PABC) in mid 30s. Even-though rare disease, classified under hormone receptor negative status which metastasis quickly to other parts by extra cellular matrix degradation. Hence it is important to find an optimal treatment option for a PABC patient. Also additional care should be taken to choose the drug; in order to avoid fetal malformation and post-partum stage side-effects. The adaptation of target based therapy in the clinical practice may help to substitute the mastectomy treatment. Recent studies suggested that certain altered Post Translational Modifications (PTMs) may be an indicative of breast cancer progression; an attempt is made to consider the over represented PTM as a parameter for gene selection. The public dataset of PABC from GEO were examined to select Differentially Expressed Genes (DEG). The corresponding PTMs for DEG were collected and association between them was found using data mining technique. Usually clustering algorithm has been applied for the study of gene expression with drawback of clustering of gene products based on specified features. But association rule mining method overcome this shortcoming and determines the useful and in depth relationships. From the association, genes were selected to study the interactions and pathways. These studies emphasis that the genes KLF12, FEN1 MUC1 and SP110, can be chosen as target, which control cancer development, without any harm to pregnancy as well as fetal developmental process.

Relationship between KLF4 and primary hepatocellular carcinoma

Kruppel-like factors (KLFs) are a family of transcription factors with zinc finger structure, which play a key role in cell proliferation, apoptosis, differentiation and embryonic development. KLF4 is an important member of the KLF family, and it is highly expressed in primary hepatocellular carcinoma tissues. However, the mechanism of KLF4 in primary hepatocellular carcinoma remains to be explored. This paper reviews the biological function of KLF4 in primary hepatocellular carcinoma.

Spatiotemporally Regulated Ablation of Klf4 in Adult Mouse Corneal Epithelial Cells Results in Altered Epithelial Cell Identity and Disrupted Homeostasis

PURPOSE

In previous studies, conditional disruption of Klf4 in the developing mouse ocular surface from embryonic day 10 resulted in corneal epithelial fragility, stromal edema, and loss of conjunctival goblet cells, revealing the importance of Klf4 in ocular surface maturation. Here, we use spatiotemporally regulated ablation of Klf4 to investigate its functions in maintenance of adult corneal epithelial homeostasis.

METHODS

Expression of Cre was induced in ternary transgenic (Klf4(LoxP/LoxP)/Krt12(rtTA/rtTA)/Tet-O-Cre) mouse corneal epithelium by doxycycline administered through intraperitoneal injections and drinking water, to generate corneal epithelium-specific deletion of Klf4 (Klf4(Δ/ΔCE)). Corneal epithelial barrier function was tested by fluorescein staining. Expression of selected Klf4-target genes was determined by quantitative PCR (QPCR), immunoblotting, and immunofluorescent staining.

RESULTS

Klf4 was efficiently ablated within 5 days of doxycycline administration in adult Klf4(Δ/ΔCE) corneal epithelium. The Klf4(Δ/ΔCE) corneal epithelial barrier function was disrupted, and the basal cells were swollen and rounded after 15 days of doxycycline treatment. Increased numbers of cell layers and Ki67-positive proliferating cells suggested deregulated Klf4(Δ/ΔCE) corneal epithelial homeostasis. Expression of tight junction proteins ZO-1 and occludin, desmosomal Dsg and Dsp, basement membrane laminin-332, and corneal epithelial-specific keratin-12 was decreased, while that of matrix metalloproteinase Mmp9 and noncorneal keratin-17 increased, suggesting altered Klf4(Δ/ΔCE) corneal epithelial cell identity.

CONCLUSIONS

Ablation of Klf4 in the adult mouse corneas resulted in the absence of characteristic corneal epithelial cell differentiation, disrupted barrier function, and squamous metaplasia, revealing that Klf4 is essential for maintenance of the adult corneal epithelial cell identity and homeostasis.

The laminin response in inflammatory bowel disease: protection or malignancy?

Laminins (LM), basement membrane molecules and mediators of epithelial-stromal communication, are crucial in tissue homeostasis. Inflammatory Bowel Diseases (IBD) are multifactorial pathologies where the microenvironment and in particular LM play an important yet poorly understood role in tissue maintenance, and in cancer progression which represents an inherent risk of IBD. Here we showed first that in human IBD colonic samples and in murine colitis the LMα1 and LMα5 chains are specifically and ectopically overexpressed with a concomitant nuclear p53 accumulation. Linked to this observation, we provided a mechanism showing that p53 induces LMα1 expression at the promoter level by ChIP analysis and this was confirmed by knockdown in cell transfection experiments. To mimic the human disease, we induced colitis and colitis-associated cancer by chemical treatment (DSS) combined or not with a carcinogen (AOM) in transgenic mice overexpressing LMα1 or LMα5 specifically in the intestine. We demonstrated that high LMα1 or LMα5 expression decreased susceptibility towards experimentally DSS-induced colon inflammation as assessed by histological scoring and decrease of pro-inflammatory cytokines. Yet in a pro-oncogenic context, we showed that LM would favor tumorigenesis as revealed by enhanced tumor lesion formation in both LM transgenic mice. Altogether, our results showed that nuclear p53 and associated overexpression of LMα1 and LMα5 protect tissue from inflammation. But in a mutation setting, the same LM molecules favor progression of IBD into colitis-associated cancer. Our transgenic mice represent attractive new models to acquire knowledge about the paradoxical effect of LM that mediate either tissue reparation or cancer according to the microenvironment. In the early phases of IBD, reinforcing basement membrane stability/organization could be a promising therapeutic approach.

Klf4 and Klf5 differentially inhibit mesoderm and endoderm differentiation in embryonic stem cells

Krüppel-like factors (Klf) 4 and 5 are two closely related members of the Klf family, known to play key roles in cell cycle regulation, somatic cell reprogramming and pluripotency. Here we focus on the functional divergence between Klf4 and Klf5 in the inhibition of mouse embryonic stem (ES) cell differentiation. Using microarrays and chromatin immunoprecipitation coupled to ultra-high-throughput DNA sequencing, we show that Klf4 negatively regulates the expression of endodermal markers in the undifferentiated ES cells, including transcription factors involved in the commitment of pluripotent stem cells to endoderm differentiation. Knockdown of Klf4 enhances differentiation towards visceral and definitive endoderm. In contrast, Klf5 negatively regulates the expression of mesodermal markers, some of which control commitment to the mesoderm lineage, and knockdown of Klf5 specifically enhances differentiation towards mesoderm. We conclude that Klf4 and Klf5 differentially inhibit mesoderm and endoderm differentiation in murine ES cells.

Generation of mice deficient in both KLF3/BKLF and KLF8 reveals a genetic interaction and a role for these factors in embryonic globin gene silencing

Krüppel-like factors 3 and 8 (KLF3 and KLF8) are highly related transcriptional regulators that bind to similar sequences of DNA. We have previously shown that in erythroid cells there is a regulatory hierarchy within the KLF family, whereby KLF1 drives the expression of both the Klf3 and Klf8 genes and KLF3 in turn represses Klf8 expression. While the erythroid roles of KLF1 and KLF3 have been explored, the contribution of KLF8 to this regulatory network has been unknown. To investigate this, we have generated a mouse model with disrupted KLF8 expression. While these mice are viable, albeit with a reduced life span, mice lacking both KLF3 and KLF8 die at around embryonic day 14.5 (E14.5), indicative of a genetic interaction between these two factors. In the fetal liver, Klf3 Klf8 double mutant embryos exhibit greater dysregulation of gene expression than either of the two single mutants. In particular, we observe derepression of embryonic, but not adult, globin expression. Taken together, these results suggest that KLF3 and KLF8 have overlapping roles in vivo and participate in the silencing of embryonic globin expression during development.

Krüppel-like factor 4 inhibits the expression of interleukin-1 beta in lipopolysaccharide-induced RAW264.7 macrophages

RAW264.7 macrophages and human peripheral blood mononuclear cells were treated with LPS to determine the expression of KLF4 and release of IL-1β. A full-length cDNA or short interference RNA of KLF4 was transfected into RAW264.7 macrophages; the expression and release of IL-1β were analyzed. The transcription and DNA binding activities of KLF4 to the IL-1β promoter were detected further. The results showed LPS treatment resulted in the increase of KLF4 level and IL-1β release; KLF4 overexpression decreased the expression of IL-1β, while KLF4 inhibition increased the expression of IL-1β; overexpression of KLF4 promoted the DNA binding activity of KLF4 to the IL-1β promoter and attenuated the transcription of IL-1β promoter, indicating an important role of KLF4 in regulating expression of IL-1β.

Regulation of corneal epithelial barrier function by Kruppel-like transcription factor 4

PURPOSE

Previously, the authors showed that Klf4-conditional null (Klf4CN) corneas display epithelial fragility. Here, they investigated the mechanism by which Klf4 regulates corneal epithelial barrier function.

METHODS

Klf4CN mice were generated by breeding Le-Cre with Klf4-LoxP mice. Fluorescein staining was used to test the corneal barrier function. RT-PCR, immunoblots, and immunofluorescence were used to detect the expression of cell junctional proteins. The effect of Klf4 on promoter activities was measured by transient cotransfection assays. Trans-epithelial electrical resistance (TEER) was used to measure the barrier-forming ability of control or anti-KLF4 siRNA-treated cells.

RESULTS

Increased fluorescein staining and decreased tight junction protein Tjp1 expression demonstrated that the Klf4CN corneal epithelial barrier function is defective. Expression of desmosomal components Dsp, Dsg-1a, and Dsg-1b was downregulated in the Klf4CN corneas, and their corresponding promoter activities were upregulated by Klf4 in transient cotransfection assays. Hemidesmosomal α3- and β4-integrin levels were not affected even though there were fewer hemidesmosomes in the Klf4CN corneas. The basement membrane components laminin-α5, -α3, -β3, and -β1-1 were downregulated, suggesting that the disrupted basement membrane is responsible for fewer hemidesmosomes in the Klf4CN cornea. Tight junction proteins OCLN1 and TJP1were downregulated in anti-KLF4 siRNA-treated cells, which failed to develop epithelial barrier function as measured by TEER.

CONCLUSIONS

Klf4 contributes to corneal epithelial barrier function by upregulating the expression of functionally related subsets of cell junctional proteins and basement membrane components.

Mammalian Krüppel-like factors in health and diseases

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, growth, development, survival, and responses to external stress. Seventeen mammalian KLFs have been identified, and numerous studies have been published that describe their basic biology and contribution to human diseases. KLF proteins have received much attention because of their involvement in the development and homeostasis of numerous organ systems. KLFs are critical regulators of physiological systems that include the cardiovascular, digestive, respiratory, hematological, and immune systems and are involved in disorders such as obesity, cardiovascular disease, cancer, and inflammatory conditions. Furthermore, KLFs play an important role in reprogramming somatic cells into induced pluripotent stem (iPS) cells and maintaining the pluripotent state of embryonic stem cells. As research on KLF proteins progresses, additional KLF functions and associations with disease are likely to be discovered. Here, we review the current knowledge of KLF proteins and describe common attributes of their biochemical and physiological functions and their pathophysiological roles.

Esophageal squamous cell dysplasia and delayed differentiation with deletion of krüppel-like factor 4 in murine esophagus

BACKGROUND & AIMS

Krüppel-like factor 4 (Klf; previously known a gut-enriched Krüppel-like factor) is a DNA-binding transcriptional regulator highly expressed in skin and gastrointestinal epithelia, specifically in regions of cellular differentiation. Homozygous null mice for Klf4 die shortly after birth from skin defects, precluding their analysis at later stages. The aim of this study was to analyze the function of Klf4 in keratinocyte biology and epithelial homeostasis in the adult by focusing on the squamous lined esophagus.

METHODS

By using the ED-L2 promoter of Epstein-Barr virus to drive Cre, we obtained tissue-specific ablation of Klf4 in the squamous epithelia of the tongue, esophagus, and forestomach.

RESULTS

Mice with loss of Klf4 in esophageal epithelia survived to adulthood, bypassing the early lethality. Tissue-specific Klf4 knockout mice had increased basal cell proliferation and a delay in cellular maturation; these mice developed epithelial hypertrophy and subsequent dysplasia by 6 months of age. Moreover, loss of Klf4 in vivo was associated with increased expression of the pro-proliferative Klf5, and Klf4 down-regulated Klf5 both transcriptionally and posttranscriptionally. By using gene expression profiling, we also showed decreased expression of critical late-stage differentiation factors and identified alterations of several genes important in cellular differentiation.

CONCLUSIONS

Klf4 is essential for squamous epithelial differentiation in vivo and interacts with Klf5 to maintain normal epithelial homeostasis.

The role of the basement membrane as a modulator of intestinal epithelial-mesenchymal interactions

Intestinal development is a process of continuous dynamic bidirectional crosstalk between epithelial and underlying mesenchymal cells. This crosstalk is mediated by well-dissected signaling pathways. Another crucial actor in the epithelio-mesenchymal interactions is the stromal microenvironment, which is composed of extracellular matrix molecules. Among them, the basement membrane (BM) molecules are secreted by the epithelium and mesenchyme in a complementary manner. These molecules signal back to the cells via the integrins or other specific receptors. In this review, we mainly focus on the BM molecules, particularly laminins. The major BM molecules are organized in a complex molecular network, which is highly variable among organs. Cell culture, coculture, and grafting models have been of great interest in understanding the importance of these molecules. Mouse gene ablation of laminin chains are interesting models, which often lead to embryonic death and are frequently accompanied by compensatory processes. Overall, the BM molecules have a crucial role in the careful maintenance of intestinal homeostasis.

Sonic hedgehog-dependent synthesis of laminin alpha1 controls basement membrane assembly in the myotome

Basement membranes have essential structural and signalling roles in tissue morphogenesis during embryonic development, but the mechanisms that control their formation are still poorly understood. Laminins are key components of basement membranes and are thought to be essential for initiation of basement membrane assembly. Here, we report that muscle progenitor cells populating the myotome migrate aberrantly in the ventral somite in the absence of sonic hedgehog (Shh) signalling, and we show that this defect is due to the failure to form a myotomal basement membrane. We reveal that expression of Lama1, which encodes laminin alpha1, a subunit of laminin-111, is not activated in Shh(-/-) embryos. Recovery of Lama1 expression or addition of exogenous laminin-111 to Shh(-/-);Gli3(-/-) embryos restores the myotomal basement membrane, demonstrating that laminin-111 is necessary and sufficient to initiate assembly of the myotomal basement membrane. This study uncovers an essential role for Shh signalling in the control of laminin-111 synthesis and in the initiation of basement membrane assembly in the myotome. Furthermore, our data indicate that laminin-111 function cannot be compensated by laminin-511.

C-terminal binding proteins (CtBPs) attenuate KLF4-mediated transcriptional activation

We aimed to examine the physical interaction between CtBPs and KLF4 and the potential importance of this interaction. Co-immunoprecipitation indicated that CtBP1 indeed interacted with KLF4. This was supported by the co-localization of both KLF4 and CtBP1 in the promoter regions of KLF4 downstream target genes. In addition, overexpression of CtBP1 significantly decreased KLF4-mediated transcriptional activation in both an artificial (pGL5) and genuine (IAP and Keratin-4) reporter system. Mutations in the potential CtBP binding motif in KLF4 were accompanied by loss of the inhibitory effect of CtBP1 in the reporter assay and of the physical interaction with CtBP1. Overall, our results suggest that CtBPs attenuate KLF4-mediated transcriptional activation through the physical interaction with KLF4.

Essential role of KLF5 transcription factor in cell proliferation and differentiation and its implications for human diseases

KLF5 (Kruppel-like factor 5) is a basic transcription factor binding to GC boxes at a number of gene promoters and regulating their transcription. KLF5 is expressed during development and, in adults, with higher levels in proliferating epithelial cells. The expression and activity of KLF5 are regulated by multiple signaling pathways, including Ras/MAPK, PKC, and TGFbeta, and various posttranslational modifications, including phosphorylation, acetylation, ubiquitination, and sumoylation. Consistently, KLF5 mediates the signaling functions in cell proliferation, cell cycle, apoptosis, migration, differentiation, and stemness by regulating gene expression in response to environment stimuli. The expression of KLF5 is frequently abnormal in human cancers and in cardiovascular disease-associated vascular smooth muscle cells (VSMCs). Due to its significant functions in cell proliferation, survival, and differentiation, KLF5 could be a potential diagnostic biomarker and therapeutic target for cancer and cardiovascular diseases.

KLF4 promotes the expression, translocation, and releas eof HMGB1 in RAW264.7 macrophages in response to LPS

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor with diverse regulatory functions in cell growth, proliferation, differentiation, and embryogenesis. In our previous study, we found that KLF4 mRNA was up-regulated more than 10-fold in adult mice lung tissues after endotoxin stimuli, and that KLF4 can regulate the expression of IL -10, an early inflammatory mediator. To determine whether KLF4 influences the expression and release of high-mobility group box 1 (HMGB1), an important late inflammatory mediator, which contains two potential KLF4-binding elements in its promoter, pcDNA3.1-KLF4 expression plasmid or KLF4 antisense oligonucleotide was transfected into RAW264.7 macrophages, the expression and release of HMGB1 were examined by reverse-transcriptase-polymerase chain reaction and Western blot, respectively. Electrophoretic mobility shift assay was performed to detect the binding activity of KLF4 to the HMGB1 promoter. The results showed that KLF4 overexpression led to an increased expression of HMGB1 in both cytoplasm and nucleus, whereas KLF4 deficiency led to a decrease in HMGB1. Moreover, compared with the control group, the release of HMGB1 was increased after KLF4 overexpression after LPS treatment, whereas the release of HMGB1 was decreased after KLF4 deficiency in response to LPS. Electrophoretic mobility shift assay results showed the binding of KLF4 to the oligonucleotides designed according to the HMGB1 promoter, and the binding activity was increased in response to LPS stimulation. These results indicate that KLF4 plays an important role in regulating the expression of HMGB1 in normal condition, as well as the translocation and release of HMGB1 in response to LPS.

The Krüppel-like factor 9 (KLF9) network in HEC-1-A endometrial carcinoma cells suggests the carcinogenic potential of dys-regulated KLF9 expression

BACKGROUND

Krüppel-like factor 9 (KLF9) is a transcriptional regulator of uterine endometrial cell proliferation, adhesion and differentiation; processes essential for pregnancy success and which are subverted during tumorigenesis. The network of endometrial genes controlled by KLF9 is largely unknown. Over-expression of KLF9 in the human endometrial cancer cell line HEC-1-A alters cell morphology, proliferative indices, and differentiation, when compared to KLF9 under-expressing HEC-1-A cells. This cell line provides a unique model for identifying KLF9 downstream gene targets and signaling pathways.

METHODS

HEC-1-A sub-lines differing in relative levels of KLF9 were subjected to microarray analysis to identify differentially-regulated RNAs.

RESULTS

KLF9 under-expression induced twenty four genes. The KLF9-suppressed mRNAs encode protein participants in: aldehyde metabolism (AKR7A2, ALDH1A1); regulation of the actin cytoskeleton and cell motility (e.g., ANK3, ITGB8); cellular detoxification (SULT1A1, ABCC4); cellular signaling (e.g., ACBD3, FZD5, RAB25, CALB1); and transcriptional regulation (PAX2, STAT1). Sixty mRNAs were more abundant in KLF9 over-expressing sub-lines. The KLF9-induced mRNAs encode proteins which participate in: regulation and function of the actin cytoskeleton (COTL1, FSCN1, FXYD5, MYO10); cell adhesion, extracellular matrix and basement membrane formation (e.g., AMIGO2, COL4A1, COL4A2, LAMC2, NID2); transport (CLIC4); cellular signaling (e.g., BCAR3, MAPKAPK3); transcriptional regulation [e.g., KLF4, NR3C1 (glucocorticoid receptor), RXRalpha], growth factor/cytokine actions (SLPI, BDNF); and membrane-associated proteins and receptors (e.g., CXCR4, PTCH1). In addition, the abundance of mRNAs that encode hypothetical proteins (KLF9-inhibited: C12orf29 and C1orf186; KLF9-induced: C10orf38 and C9orf167) were altered by KLF9 expression. Human endometrial tumors of high tumor grade had decreased KLF9 mRNA abundance.

CONCLUSION

KLF9 influences the expression of uterine epithelial genes through mechanisms likely involving its transcriptional activator and repressor functions and which may underlie altered tumor biology with aberrant KLF9 expression.

Roles of Krüpel-like factor 4 in normal homeostasis, cancer and stem cells

Krüpel-like factor 4 (KLF4) is a zinc finger-type transcription factor expressed in a variety of tissues, including the epithelium of the intestine and the skin, and it plays an important role in differentiation and cell cycle arrest. Depending on the gene targeted, KLF4 can both activate and repress transcription. Moreover, in certain cellular contexts, KLF4 can function as a tumor suppressor or an oncogene. Finally, KLF4 is important in reprogramming differentiated fibroblasts into inducible pluripotent stem cells, which highly resemble embryonic stem cells. This review summarizes what is known about the diverse functions of KLF4 as well as their molecular mechanisms.

KLF4 regulates the expression of interleukin-10 in RAW264.7 macrophages

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor. In the current study, RAW264.7 murine macrophages were treated with Escherichia coli lipopolysaccharide (LPS) to determine the expression of KLF4. A full-length cDNA or antisense oligonucleotides of KLF4 was transfected into RAW264.7 macrophages, and the expression and release of IL-10 were analyzed by RT-PCR and ELISA. The transcription and DNA binding activities of KLF4 to the IL-10 promoter were detected by the luciferase reporter and electrophoretic mobility shift assays. The results showed that treatment of RAW264.7 macrophages with LPS resulted in a dose- and time-dependent increase in KLF4 protein levels; KLF4 overexpression increased the expression of IL-10, while KLF4 inhibition decreased the expression of IL-10. The overexpression of KLF4 promoted the transcription and DNA binding activities of KLF4 to the IL-10 promoter. These results indicate that KLF4 plays an important role in regulating the expression of IL-10.

The diverse functions of Krüppel-like factors 4 and 5 in epithelial biology and pathobiology

The Krüppel-like factors (KLFs) comprise a family of evolutionarily conserved zinc finger transcription factors that regulate numerous biological processes including proliferation, differentiation, development and apoptosis. KLF4 and KLF5 are two closely related members of this family and are both highly expressed in epithelial tissues. In the intestinal epithelium, KLF4 is expressed in terminally differentiated epithelial cells at the villus borders of the mucosa and inhibits cell growth, while KLF5 is expressed in proliferating epithelial cells at the base of the intestinal crypts and promotes cell growth. KLF4 and KLF5 respond to a myriad of external stress stimuli and are likely involved in restoring cellular homeostasis following exposure to stressors. Confirming their importance in maintaining tissue integrity, KLF4 and KLF5 are both dysregulated in various types of cancer. Here we review the recent advances in defining the physiological and pathobiological roles of KLF4 and KLF5, focusing on their functions in the intestinal epithelium.

Overexpression of Kruppel-like factor 5 in esophageal epithelia in vivo leads to increased proliferation in basal but not suprabasal cells

Krüppel-like factor 5 (Klf5; also called IKLF or BTEB2), a zinc-finger transcription factor with proproliferative and transforming properties in vitro, is expressed in proliferating cells of gastrointestinal tract epithelia, including in basal cells of the esophagus. Thus, Klf5 is an excellent candidate to regulate esophageal epithelial proliferation in vivo. Nonetheless, the function of Klf5 in esophageal epithelial homeostasis and tumorigenesis in vivo has not previously been determined. Here, we used the ED-L2 promoter of the Epstein-Barr virus to express Klf5 throughout esophageal epithelia. ED-L2/Klf5 transgenic mice were born at the appropriate Mendelian ratio, survived to at least 1 yr of age, and showed no evidence of esophageal dysplasia or cancer. Staining for bromodeoxyuridine (BrdU) demonstrated increased proliferation in the basal layer of ED-L2/Klf5 mice, but no proliferation was seen in suprabasal cells, despite ectopic expression of Klf5 in these cells. Notably, expression of the KLF family member Klf4, which binds the same DNA sequences as Klf5 and which inhibits proliferation and promotes differentiation, was not altered in ED-L2/Klf5 transgenic mice. In primary esophageal keratinocytes that overexpressed Klf5, expression of Klf4 still inhibited proliferation and promoted differentiation, providing a possible mechanism for the persistence of keratinocyte differentiation in ED-L2/Klf5 mice. To identify additional targets for Klf5 in esophageal epithelia, we performed functional genomic analyses and identified a total of 15 differentially expressed genes. In summary, while Klf5 positively regulates proliferation in basal cells, it is not sufficient to maintain proliferation in the esophageal epithelium.

Erythroid Krüppel-like factor directly activates the basic Krüppel-like factor gene in erythroid cells

The Sp/Krüppel-like factor (Sp/Klf) family is comprised of around 25 zinc finger transcription factors that recognize CACCC boxes and GC-rich elements. We have investigated basic Krüppel-like factor (Bklf/Klf3) and show that in erythroid tissues its expression is highly dependent on another family member, erythroid Krüppel-like factor (Eklf/Klf1). We observe that Bklf mRNA is significantly reduced in erythroid tissues from Eklf-null murine embryos. We find that Bklf is driven primarily by two promoters, a ubiquitously active GC-rich upstream promoter, 1a, and an erythroid downstream promoter, 1b. Transcripts from the two promoters encode identical proteins. Interestingly, both the ubiquitous and the erythroid promoter are dependent on Eklf in erythroid cells. Eklf also activates both promoters in transient assays. Experiments utilizing an inducible form of Eklf demonstrate activation of the endogenous Bklf gene in the presence of an inhibitor of protein synthesis. The kinetics of activation are also consistent with Bklf being a direct Eklf target. Chromatin immunoprecipitation assays confirm that Eklf associates with both Bklf promoters. Eklf is typically an activator of transcription, whereas Bklf is noted as a repressor. Our results support the hypothesis that feedback cross-regulation occurs within the Sp/Klf family in vivo.

Tough beginnings: alterations in the transcriptome of cloned embryos during the first two cell cycles

Cloned embryos produced by somatic cell nuclear transfer (SCNT) display a plethora of phenotypic characteristics that make them different from fertilized embryos, indicating defects in the process of nuclear reprogramming by the recipient ooplasm. To elucidate the extent and timing of nuclear reprogramming, we used microarrays to analyze the transcriptome of mouse SCNT embryos during the first two cell cycles. We identified a large number of genes mis-expressed in SCNT embryos. We found that genes involved in transcription and regulation of transcription are prominent among affected genes, and thus may be particularly difficult to reprogram, and these likely cause a ripple effect that alters the transcriptome of many other functions, including oxidative phosphorylation, transport across membrane, and mRNA transport and processing. Interestingly, we also uncovered widespread alterations in the maternal (i.e., non-transcribed) mRNA population of SCNT embryos. We conclude that gene expression in early SCNT embryos is grossly abnormal, and that this is at least in part the result of incomplete reprogramming of transcription factor genes.

The Sp family of transcription factors regulates the human laminin alpha1 gene in JAR choriocarcinoma cells

Laminin-111 (alpha1beta1gamma1) is the major component of the embryonic and extra-embryonic basement membrane. The laminin alpha1 chain shows a restricted and developmentally regulated expression in basement membranes of distinct epithelial tissues while beta1 and gamma1 chains have a wide tissue distribution. To understand how human laminin alpha1 chain expression is controlled, we cloned and characterized the 5'-flanking region of the human laminin alpha1 (LAMA1) gene. Transfection studies using serially deleted promoter constructs and JAR choriocarcinoma cells revealed that the minimal promoter fragment resided in the +31 to -206 region, which contains a number of GC- and GT/A-rich motifs for the binding of the Sp family of transcription factors. Electrophoretic mobility shift assays and mutational analyses revealed that Sp1 and Sp3 bound specifically to these elements and are important for the promoter activity. Furthermore, we showed that Krüppel-like factors KLF4 and KLF6 also activate transcription of the human LAMA1 gene. Chromatin immunoprecipitation analysis demonstrated recruitment of these transcription factors to the promoter region. These results indicate that transcription of the human LAMA1 gene is controlled by a combination of the actions of Sp1/Sp3 and Krüppel-like factors, KLF4 and KLF6.

Effect of laminin-1 on intestinal cell differentiation involves inhibition of nuclear nucleolin

Intestinal epithelial cells are characterized by continuous renewal and differentiation events, which may be influenced by the basement membrane, and in particular laminins, which are major components of this specialized extracellular matrix. The function and signaling pathways of laminins in these processes are still poorly documented. In this study, we investigated the possible role and the subcellular localization of nucleolin, a nuclear shuttling protein, in relation to differentiation of human intestinal epithelial Caco2/TC7 cells triggered by exogenous laminin-1. Immunofluorescence and Western blot analysis indicated that laminin-1 induced early differentiation of the cells concomitantly to a decrease in nuclear nucleolin and its a cell surface location. We also showed that both effects of laminin-1 on Caco2/TC7 cells--induction of the differentiation marker sucrase-isomaltase and redistribution of nucleolin--could be mediated by a beta1-integrin dependent cascade that implicated activation of the p38 MAPK pathway. In addition, knock-down of nucleolin expression by the small interfering RNA strategy mimicked the effect of laminin-1 as it resulted in the induction of cell polarization and differentiation. Thus, our study suggests that changes in the subcellular distribution and expression level of nucleolin play an important role in intestinal cell differentiation and relay the signaling pathway induced by laminin-1.

Transcriptional profiling of the cell cycle checkpoint gene krüppel-like factor 4 reveals a global inhibitory function in macromolecular biosynthesis

Krüppel-like factor 4 (KLF4; also known as gut-enriched Krüppel-like factor or GKLF) is known to exhibit checkpoint function during the G1/S and G2/M transitions of the cell cycle. The mechanism by which KLF4 exerts these effects is not fully established. Here we investigated the expression profile of KLF4 in an inducible system over a time course of 24 h. Using oligonucleotide microarrays, we determined that the fold changes relative to control in expression levels of KLF4 exhibited a time-dependent increase from 3- to 20-fold between 4 and 24 h following KLF4 induction. During this period and among a group of 473 cell cycle regulatory genes examined, 96 were positively correlated and 86 were negatively correlated to KLF4's expression profile. Examples of upregulated cell cycle genes include those encoding tumor suppressors such as MCC and FHIT, and cell cycle inhibitors such as CHES1 and CHEK1. Examples of downregulated genes include those that promote the cell cycle including several cyclins and those required for DNA replication. Unexpectedly, several groups of genes involved in macromolecular synthesis, including protein biosynthesis, transcription, and cholesterol biosynthesis, were also significantly inhibited by KLF4. Thus, KLF4 exerts a global inhibitory effect on macromolecular biosynthesis that is beyond its established role as a cell cycle inhibitor.

KLF4, p21 and context-dependent opposing forces in cancer

Krüppel-like factors are transcriptional regulators that influence several cellular functions, including proliferation. Recent studies have shown that one family member, KLF4, can function both as a tumour suppressor and an oncogene. The ability of KLF4 to affect the levels of expression of the cell-cycle regulator p21 seems to be involved, in that this protein might function as a switch that determines the outcome of KLF4 signalling. Is this role of p21 restricted to KLF4, or does p21 represent a nodal point for signals from multiple other factors with opposing functions in cancer?

Generation of a conditionally null allele of the laminin alpha1 gene

Laminins are heterotrimeric glycoproteins of the basement membranes. Laminin 1 (alpha1, beta1, gamma1) is the major laminin expressed during early mouse embryogenesis. To gain access to the physiological function of laminin alpha1 chain, we developed a conditionally null allele of its encoding gene (Lama1) using the cre/loxP system. Floxed-allele-carrying mice (Lama1(flox/flox)) display no overt phenotype. Lama1(flox/flox) mice were crossed with transgenic deleter mice (CMV-Cre) to generate Lama1-deficient mice (Lama1(Delta/Delta)). Lama1(Delta/Delta) embryos die during the early postimplantation period after embryonic day 6.5. They lack Reichert's membrane, an extraembryonic basement membrane in which laminin alpha1 is normally highly expressed. In parallel, Lama1(Delta/Delta) embryos display 1) parietal and visceral endoderm differentiation defects with altered expression of cytokeratin 19 and GATA4, respectively, and 2) an induction of apoptosis. This new mouse model is of particular interest as it will allow time- and tissue-specific inactivation of the Lama1 gene in various organs.

Krüppel-like factors 4 and 5: the yin and yang regulators of cellular proliferation

Krüppel-like factors (KLFs) are evolutionarily conserved zinc finger-containing transcription factors with diverse regulatory functions in cell growth, proliferation, differentiation, and embryogenesis. KLF4 and KLF5 are two closely related members of the KLF family that have a similar tissue distribution in embryos and adults. However, the two KLFs often exhibit opposite effects on regulation of gene transcription, despite binding to similar, if not identical, cis-acting DNA sequences. In addition, KLF4 and 5 exert contrasting effects on cell proliferation in many instances; while KLF4 is an inhibitor of cell growth, KLF5 stimulates proliferation. Here we review the biological properties and biochemical mechanisms of action of the two KLFs in the context of growth regulation.

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