Transcription factor NF-Y regulates differentiation of CaCo-2 cells

The CaCo-2 cell line is used to study the molecular mechanisms underlying differentiation of intestinal epithelial cells. These cells undergo a gradual differentiation process that is growth-related and depends on cellular density. CaCo-2 cells acquire a morphological polarity and express such markers of mature enterocytes as sucrase-isomaltase, apolipoproteins, alkaline phosphatase, and H-ferritin. Because the NF-Y transcription factor is required for H-ferritin gene expression, we investigated whether it is involved in the expression of the other CaCo-2 differentiation markers. We observed that subunit NF-YA increases during CaCo-2 differentiation and that the constitutive expression of NF-YA, obtained in stably transfected CaCo-2 cells, results in the expression of differentiation markers. In fact, sucrase-isomaltase, apolipoprotein A1, and H-ferritin were constitutively expressed in NF-YA-transfected cells and their levels did not increase during prolonged culture, while these markers were not expressed in mock-transfected CaCo-2 cells or transfected with an inactive NF-YA expression vector until the onset of differentiation.

The B subunit of the CAAT-binding factor NFY binds the central segment of the Co-activator p300

We report that the heterotrimeric transcription factor NFY or "CAAT-binding factor" binds the -60 region of the human H ferritin promoter, the B site. DNA binding analysis with specific antibodies demonstrates that NFY/B/C subunits tightly bind this site and that NFY/C subunit is masked in vivo by binding with other protein(s). NFY binds the co-activator p300. Specifically, the NFY/B subunit interacts with the central segment of p300 in vivo and in vitro. cAMP substantially increases the formation of the NFY.p300 complex. Taken together these data provide a general model of cAMP induction of non-CRE-containing promoters and suggest that the NFY-B.p300 complex is located at the 5' end of the promoter and the NFY-B.C. TFIIB on the 3' end toward the transcription start site.

P/CAF/p300 complex binds the promoter for the heavy subunit of ferritin and contributes to its tissue-specific expression

We analysed the role of the nuclear protein P/CAF in regulating the transcription of the gene for human heavy (H) ferritin in given cell types. P/CAF is a histone acetylase, recruited to specific promoters via interaction with the co-activator molecule p300/CREB-binding protein (CBP). Histone acetylation promoted by P/CAF destabilizes the nucleosome structure, thus contributing to activation of transcription. The transcription of the H ferritin gene is regulated by the transcription factor B-box-binding factor (Bbf), which bridges RNA polymerase II via p300/CBP. Northern blot analyses of RNA species from various human tissues and cell lines demonstrate that the H ferritin gene is expressed at high levels in cells containing high levels of the P/CAF transcript. Moreover, transient overexpression of P/CAF in cells constitutively expressing low levels of this protein activates transcription driven by the region of the H promoter interacting with Bbf. The involvement of p300/CBP in the possible P/CAF-mediated regulation of H promoter was also explored by evaluating the phenomenon in the presence of the oncoprotein E1A. The results of these experiments demonstrate that P/CAF activates the H promoter also in the presence of limited amounts of p300/CBP. We argue that P/CAF is a component of the basal transcription apparatus of the H ferritin gene and that the relative amounts of the P/CAF protein in different cell types could account for the cell-specific control of the H ferritin gene transcription.

Okadaic acid stimulates H ferritin transcription in HeLa cells by increasing the interaction between the p300 CO-activator molecule and the transcription factor Bbf

The transcription of the human H ferritin gene is regulated by a transcription factor, called Bbf, which binds an enhancer element located in the -100/+1 region of the H promoter. To evaluate a possible role of Bbf phosphorylation on the promoter efficiency, we exposed HeLa cells to the phosphatase inhibitor okadaic acid (OA). The okadaic acid treatment increased about 4-fold the transcription driven by the -100/+1 region of the H promoter. However, the DNA binding activity of Bbf was not modified by OA, as assessed by EMSA. Immunoprecipitation experiments demonstrated that the OA-treatment stimulates and/or stabilizes the complex between Bbf and the nuclear protein p300, most probably by inducing the phosphorylation state of the complex. Bbf depends on the p300 molecule to trigger RNA polymerase II and thus transcription of the H ferritin gene.

A common mechanism underlying the E1A repression and the cAMP stimulation of the H ferritin transcription

Transcription of the H ferritin gene in vivo is stimulated by cAMP and repressed by the E1A oncoprotein. We report here the identification of the cis-element in the human promoter responsive to both cAMP- and E1A-mediated signals. This promoter region is included between positions -62 to -45 and binds a approximate 120-kDa transcription factor called Bbf. Bbf forms a complex in vivo with the coactivator molecules p300 and CBP. Recombinant E1A protein reduces the formation of these complexes. In vivo overexpression of p300 in HeLa cells reverses the E1A-mediated inhibition of the ferritin promoter transcription driven by Bbf. These data suggest the existence of a common mechanism for the cAMP activation and the E1A-mediated repression of H ferritin transcription.

Transcriptional activation of the H-ferritin gene in differentiated Caco-2 cells parallels a change in the activity of the nuclear factor Bbf

In this paper, we examine the mechanisms that regulate the expression of the heavy (H) ferritin subunit in the colon carcinoma Caco-2 cell line allowed to differentiate spontaneously in vitro. The differentiation process of these cells in continuous culture is accompanied by an accumulation of the mRNA coding for the apoferritin H chain. The analysis of Caco-2 subclones stably transfected with an H-chain promoter-chloramphenicol acetyltransferase (CAT) construct revealed that the mRNA increase is paralleled by an enhanced transcription of the H gene, driven by the -100 to +4 region of the H promoter. The H gene transcriptional activation seems to be a specific feature of differentiated Caco-2 cells, since the activity of other promoters did not change upon differentiation. The -100 to +4 region of the H promoter binds a transcription factor called Bbf (B-box binding factor); electrophoretic-mobility-shift-assay analyses showed that the retarded complex due to Bbf-H promoter interaction is significantly increased in the differentiated cells. We propose that the activation of H-ferritin gene expression may be associated with the establishment of a differentiated phenotype in Caco-2 cells, and that the H-ferritin gene transcriptional up-regulation is accompanied by a modification in the activity of the transcription factor Bbf.

Negative and positive elements in the promoter region of the human apoferritin L gene

We have characterized the promoter of the human gene coding for the apoferritin L subunit. Transient transfections of 5' and 3' deletion mutants indicate that the efficiency of the L promoter depends on both negative and positive cis-elements, located upstream and downstream of the transcription start point. DNaseI footprinting analysis of this DNA region revealed the presence of five protected segments. The most upstream one (element 1) corresponds to the negative cis-element and is recognized by factor(s) sharing a GC-sequence specificity. Three positive elements are in the region upstream of the start of transcription; a fifth positive cis-element (element 5) is localized in the first exon of the L gene.

PCR analysis of the H ferritin multigene family reveals the existence of two classes of processed pseudogenes

The human gene coding for the apoferritin H subunit belongs to a complex multigene family constituted by the expressed gene and by an undefined number of pseudogenes. We have used a strategy based on PCR to amplify specifically the H pseudogenes from a sample of human genomic DNA. With this approach, three new H pseudogenes have been cloned and characterized by DNA sequence analysis. In addition, we have identified a new type of pseudogene, the size of which (700 bp) is caused by multiple detection events in the putative coding region.

Transcriptional regulation of the human H ferritin-encoding gene (FERH) in G418-treated cells: role of the B-box-binding factor

We have analysed the molecular basis underlying the increase in ferritin heavy-chain mRNA (FERH) levels in cells exposed to the antibiotic Geneticin (G418). Transient transfection experiments demonstrate that this increase is paralleled by an enhanced transcription driven by the promoter (pFERH) for the human FERH gene, in which the most proximal promoter element (B-box) appears to play a key role. This region is conserved in human and rat, and binds an unknown factor. The DNA-protein complex composed of B-box-binding factor and its cis-element becomes more abundant in the G418-treated cells, as compared with the untreated ones.

Promoter for the human ferritin heavy chain-encoding gene (FERH): structural and functional characterization

We conducted a functional analysis of the promoter for the human ferritin heavy chain-encoding gene (pFERH) in HepG2 and HeLa cells. The activity of pFERH is equivalent in both cell types, despite their different ferritin (Fer) isotypes. Transfections of a series of 5'-deletion mutants indicate that pFERH activity is essentially dependent on two motifs. One of them, accounting for about 50% of the total transcriptional activity, is recognized by the RNA polymerase II transcription factor, Sp1, and the other by a low-affinity factor present in both the cell types analyzed.

Regulation and expression of type V (tartrate-resistant) acid phosphatase in human mononuclear phagocytes

Human type V (tartrate-resistant) acid phosphatase belongs to a unique group of iron-binding proteins that includes uteroferrin and other purple phosphatases. The enzyme is normally restricted to osteoclasts and certain phagocytic cells but its rôle is unknown. We show that phosphatase mRNA is abundant in cells of monohistiocytic phenotype and that enzyme expression in cultured human monocyte-derived macrophages is depressed by gamma-interferon and bacterial lipopolysaccharide, agents that promote functional differentiation in these cells. In contrast, phorbol ester, which stimulates intracellular calcium-mediated events, greatly enhances type V phosphatase expression and mRNA abundance. Lymphokine and phorbol ester-modulated expression of type V acid phosphatase expression thus represents a model system for investigating proliferative responses that are specific to cells of the mononuclear macrophage system.

Type 5 acid phosphatase. Sequence, expression and chromosomal localization of a differentiation-associated protein of the human macrophage

The purple acid phosphatases and uteroferrin belong to a diverse multifunctional class of binuclear iron-containing proteins that includes haemerythrin and ribonucleotide reductase. In the pig, uteroferrin has been implicated in the delivery of iron to the foetus, but the role of the related human type 5 acid phosphatase that is principally found in resident tissue macrophages is not yet clear. To define further the function of this metalloenzyme, we have isolated and sequenced a cDNA clone for type 5 acid phosphatase and investigated expression of its gene in human tissues. The phosphatase clone contains an open reading frame of 975 bp and encodes a protein of 325 amino acids, including a signal peptide of 19 residues and two potential sites for N-glycosylation. The type 5 acid phosphatase gene mapped to the short arm of human chromosome 19 and was found to have a restriction fragment length polymorphism on digestion with XbaI. Expression of phosphatase mRNA was restricted to mononuclear phagocytes and the enzyme was induced greater than 20-fold on transformation of normal human monocytes to macrophages by culture in serum-supplemented medium. Type 5 acid phosphatase thus represents a tightly regulated system for the study of molecular events in the differentiation programme of the normal macrophage.

Expression of genes of ferritin subunits in human hepatoma cell lines

The expression of ferritin genes has been studied in two well differentiated hepatoma cell lines, HepG2 and Hep3B, and in an undifferentiated cell line, HepPLC/PRF/5. The steady-state level of the H and L ferritin subunit mRNAs is different in the three cell lines, being most abundant in the HepG2 and Hep3B cells. The efficiency of promotion of transcription of the H and L gene promoters is not correlated with the levels of the two transcripts; moreover the half-life of the H and L mRNAs varies among the hepatoma cells. The different level of ferritin mRNAs in differentiated and undifferentiated cells appears to be mainly due to a different stability of the transcripts.

Ferritin H and L mRNAs in human neoplastic tissues

The typical tissue isoferritin pattern varies during neoplastic transformation, usually shifting toward a more acidic profile. To investigate the molecular basis of this phenomenon, we have analyzed the steady-state levels of the H and L mRNAs in several neoplastic tissues. By using specific probes for the two ferritin subunits, we have found, in three different adenocarcinomas and in a case of Hodgkin lymphoma, a two- to four-fold increase of the H and L mRNA levels compared to those found in normal human liver.