Dendritic cells derived from peripheral monocytes express endothelial markers and in the presence of angiogenic growth factors differentiate into endothelial-like cells.

CD14-positive monocytes obtained from human peripheral blood were cultured with GM-CSF and IL-4. During the early culture phase immature dendritic cells (DCs) developed which not only expressed CD1a, HLA-DR and CD86, but also expressed the endothelial cell markers von Willebrand factor (vWF), VE-cadherin and VEGF receptors Flt-1 and Flt-4. Further maturation of DCs was achieved by prolonged cultivation with TNFalpha. These cells showed typical DC morphology and like professional antigen-presenting cells (APCs) expressed CD83 and high levels of HLA-DR and CD86. However, if immature DCs were grown with VEGF, bFGF and IGF-1 on fibronectin/vitronectin-coated culture dishes, a marked change in morphology into caudated or oval cells occurred. In the presence of these angiogenic growth factors the cultured cells developed into endothelial-like cells (ELCs), characterized by increased expression of vWF, KDR and Flt-4 and a disappearance of CD1a and CD83. Addition of IL-4 and Oncostatin M also increased VE-cadherin expression, and the loosely adherent cells formed clusters, cobblestones and network-like structures. vWF- expressing ELCs mainly originated from CD1a-positive cells, and VEGF was responsible for the decrease in the expression of the DC markers CD1a and CD83. In mixed leukocyte cultures, mature DCs were more potent APCs than ELCs. Moreover, Ac-LDL uptake, and the formation of tubular structures on a plasma matrix was restricted to ELCs. These results suggest that in the presence of specific cytokines immature DCs have the potential to differentiate along different lineages, i.e. into a cell type resembling ELCs.

Endothelial-like cells derived from human CD14 positive monocytes.

In the present study, we show that endothelial-like cells (ELCs) can develop from human CD14-positive mononuclear cells (CD14 cells) in the presence of angiogenic growth factors. The CD14 cells became loosely adherent within 24 h of culture and subsequently underwent a distinct process of morphological transformation to caudated or oval cells with eccentric nuclei. After 1 week in culture the cells showed a clear expression of endothelial cell markers, including von Willebrand factor (vWF), CD144 (VE-cadherin), CD105 (endoglin), acetylated low-density lipoprotein (AC-LDL)-receptor, CD36 (thrombospondin receptor), FLT-1, which is vascular endothelial cell growth factor (VEGF) receptor-1, and, to a weaker extent, KDR (VEGF receptor-2). Furthermore, in these cells structures resembling Weibel-Palade bodies at different storage stages were identified by electron microscopy, and upon culturing on three-dimensional fibrin gels the cells build network-like structures. In addition, cell proliferation and vWF expression was stimulated by VEGF, and the endothelial cell adhesion molecules CD54 (ICAM-1), and CD106 (VCAM-1) became transiently inducible by tumor necrosis factor-alpha (TNF-alpha). In contrast, the dendritic markers CD1a, and CD83 were not expressed to any significant extent. The expression of CD68, CD80 (B7-1), CD86 (B7-2), HLA-DR and CD36 may also suggest that ELCs might be related to macrophages, sinus lining or microvascular endothelial cells. Taken together, our observations indicate that ELCs can differentiate from cells of the monocytic lineage, suggesting a closer relationship between the monocyte/macrophage- and the endothelial cell systems than previously supposed.

Functional domains in cyclin D1: pRb-kinase activity is not essential for transformation.

Although cyclin D1 plays a major role during cell cycle progression and is involved in human tumourigenesis, its domain structure is still poorly understood. In the present study, we have generated a series of cyclin D1 N- and C-terminal deletion constructs. These mutants were used to define the domains required for transformation of rat embryonal fibroblasts (REF) in cooperation with activated Ha-ras and and to establish correlations with defined biochemical properties of cyclin D1. Protein binding and REF assays showed that the region of the cyclin box required for the interaction with CDK4 as well as C-terminal sequences determining protein stability were crucial for transformation. Surprisingly, however, the N-terminal deletion of 20 amino acids which impaired pRb kinase activity did not affect the transforming ability of cyclin D1. Likewise, no effect on transformation was observed with mutants defective in p21CIP interaction. These observations argue against a crucial role of pRb inactivation or p21CIP squelching in cyclin D1-mediated transformation.

CDF-1 mediated repression of cell cycle genes targets a specific subset of transactivators.

The cdc25C, cyclin A and cdc2 genes are regulated during the cell cycle through two contiguous repressor binding sites, the CDE and CHR, located in the region of transcription initiation and interacting with a factor termed CDF-1. The target of this repression seems to be transcriptional activation of these promoters by transcription factors bound upstream. The majority of these factors falls into the class of glutamine-rich activators, suggesting that CDF-1-mediated repression might be activation domain specific. In the present study we have used chimeric promoter constructs to demonstrate that the cdc25C UAS, but not the core promoter, is crucial for repression. In addition, we show that only specific transcription factors and activation domains are responsive to CDE-CHR-mediated cell cycle regulation. These observations clearly indicate that CDF-1 interferes with activation of transcription by a specific subset of transactivators. The repressible activation domains belong to the same class of glutamine-rich activators, pointing to specific interactions of CDF-1 with components of the transcription machinery. In agreement with this conclusion we find that a simple inversion of the CDF-CHR module completely abrogates cell cycle-regulated repression.

A new model of cell cycle-regulated transcription: repression of the cyclin A promoter by CDF-1 and anti-repression by E2F.

Cell cycle regulation of the cyclin A gene is determined by a bipartite repressor binding site in the region of the basal promoter, termed CDE-CHR, which also controls the expression of cell cycle genes upregulated in S or G2 (such as cdc25C). The CDE-CHR in the cyclin A promoter is recognized by both E2F complexes and CDF-1, but the contribution of each of these factors in cell cycle regulation is unknown. In the present study, we have introduced mutations into the cyclin A promoter which lead to either a loss or enhancement of E2F binding, while having only marginal effects on the interaction with CDF-1. Unlike mutants deficient for CDF-1 binding, promoter variants lacking E2F binding showed an unchanged repression in G0, thus identifying CDF-1 as the principal repressor of the cyclin A gene. The same mutants did show, however, a delayed derepression while a mutation leading to increased E2F binding resulted in premature up-regulation. These findings clearly suggest that E2F contributes to the correct timing of cyclin A transcription, presumably by acting as an anti-repressor. In agreement with this conclusion, we find that the cyclin A promoter only poorly interacts with E2F-4, which is the major E2F family member in G0 cells, while a clear binding is seen with E2F-1 and -3, which are up-regulated in late G1.

CDF-1, a novel E2F-unrelated factor, interacts with cell cycle-regulated repressor elements in multiple promoters.

The cdc25C , cdc2 and cyclin A promoters are controlled by transcriptional repression through two contiguous protein binding sites, termed the CDE and CHR. In the present study we have identified a factor, CDF-1, which interacts with the cdc25C CDE-CHR module. CDF-1 binds to the CDE in the major groove and to the CHR in the minor grove in a cooperative fashion in vitro , in a manner similar to that seen by genomic footprinting. In agreement with in vivo binding data and its putative function as a periodic repressor, DNA binding by CDF-1 in nuclear extracts is down-regulated during cell cycle progression. CDF-1 also binds avidly to the CDE-CHR modules of the cdc2 and cyclin A promoters, but not to the E2F site in the B- myb promoter. Conversely, E2F complexes do not recognize the cdc25C CDE-CHR and CDF-1 is immunologically unrelated to all known E2F and DP family members. This indicates that E2F- and CDF-mediated repression is controlled by different factors acting at different stages during the cell cycle. While E2F-mediated repression seems to be associated with genes that are up-regulated early (around mid G1), such as B- myb , CDE-CHR-controlled genes, such as cdc25C , cdc2 and cyclin A , become derepressed later. Finally, the fractionation of native nuclear extracts on glycerol gradients leads to separation of CDF-1 from both E2F complexes and pocket proteins of the pRb family. This emphasizes the conclusion that CDF-1 is not an E2F family member and points to profound differences in the cell cycle regulation of CDF-1 and E2F.

The differential binding of E2F and CDF repressor complexes contributes to the timing of cell cycle-regulated transcription.

B- myb and cdc25C exemplify different groups of genes whose transcription is consecutively up-regulated during the cell cycle. Both promoters are controlled by transcriptional repression via modules consisting of an E2F binding site (E2FBS) or the related CDE plus a contiguous CHR co-repressor element. We now show that the B- myb repressor module, which is derepressed early (mid G1), is preferentially recognized by E2F-DP complexes and that a mutation selectively abolishing E2F binding impairs regulation. In contrast, the cdc25C repressor module, which is derepressed late (S/G2), interacts selectively with CDE-CHR binding factor-1 (CDF-1). E2F binding, but not CDF-1 binding, requires specific nucleotides flanking the E2FBS/CDE core, while CDF-1 binding, but not E2F binding, depends on specific nucleotides in the CHR. Swapping these nucleotides between the two promoters profoundly changes protein binding patterns and alters expression kinetics. Thus predominant CDF-1 binding leads to derepression in late S, predominant E2F binding results in up-regulation in late G1, while promoters binding both E2F and CDF-1 with high efficiency show intermediate kinetics. Our results support a model where the differential binding of E2F and CDF-1 repressor complexes contributes to the timing of promoter activity during the cell cycle.

CDF-1-mediated repression of cell cycle genes targets a specific subset of transactivators.

The cdc25C , cyclin A and cdc2 genes are regulated during the cell cycle through two contiguous repressor binding sites, the CDE and CHR, located in the region of transcription initiation and interacting with a factor termed CDF-1. The target of this repression seems to be transcriptional activation of these promoters by transcription factors bound upstream. The majority of these factors falls into the class of glutamine-rich activators, suggesting that CDF-1-mediated repression might be activation domain specific. In the present study we have used chimeric promoter constructs to demonstrate that the cdc25C UAS, but not the core promoter, is crucial for repression. In addition, we show that only specific transcription factors and activation domains are responsive to CDE-CHR-mediated cell cycle regulation. These observations clearly indicate that CDF-1 interferes with activation of transcription by a specific subset of transactivators. The repressible activation domains belong to the same class of glutamine-rich activators, pointing to specific interactions of CDF-1 with components of the transcription machinery. In agreement with this conclusion we find that a simple inversion of the CDE-CHR module completely abrogates cell cycle-regulated repression.

Characterization of the TATA-less core promoter of the cell cycle-regulated cdc25C gene.

The TATA- and Inr-less promoter of the human cdc25C gene is regulated during the cell cycle through binding of a repressor to two contiguous promoter-proximal elements, the CDE and CHR. In this study we have characterized in detail the region of the cdc25C promoter immediately downstream of these elements. Several lines of evidence suggest that this region of approximately 60 bp acts as the core promoter. This sequence: (i) harbors most of the transcription initiation sites; (ii) possesses basal promoter activity in vivo ; (iii) shows no stable protein binding in vivo as indicated by genomic dimethyl sulfate and phenanthroline copper footprinting; (iv) contains single-stranded regions in vivo as shown by potassium permanganate footprinting; (v) is hypersensitive to DNase I cleavage in permeabilized cells. Mutational analysis of the core promoter revealed the presence of three sites which play a role in transcription. Two of these sites were found to represent low affinity binding sites for transcription factors of the Sp1 family. Mutation of these sites led to decreased levels of transcription, while their alteration to canonical Sp1 sites impaired cell cycle regulation. Thus the transient interaction of Sp1 with the core promoter appears to be necessary for maximal transcription without perturbing cell cycle regulation.

Cell cycle-regulated repression of B-myb transcription: cooperation of an E2F site with a contiguous corepressor element.

B-myb belongs to a group of cell cycle genes whose transcription is repressed in G0/early G1 through a binding site for the transcription factor E2F. Here, we show that the B-myb repressor element is specifically recognised by heterodimers consisting of DP-1 and E2F-1, E2F-3 or E2F-4. Surprisingly, E2F-mediated repression is dependent on a contiguous corepressor element that resembles the CHR previously established as a corepressor of the CDE in cell cycle genes derepressed in S/G2, such as cyclin A, cdc2 and cdc25C. A factor binding to the B-myb CHR was identified in fractionated HeLa nuclear extract and found to interact with the minor groove, as previously shown by in vivo footprinting for the cyclin A CHR. The B-myb and cdc25C CHRs are related with respect to protein binding but are functionally clearly distinct. Our results support a model where both E2F- and CDE-mediated repression, acting at different stages in the cell cycle, are dependent on promoter-specific CHR elements.

Cell cycle regulation of E2F site occupation in vivo.

DNA-binding E2F complexes have been identified throughout the mammalian cell cycle, including the transcriptionally inactive complexes with pocket proteins, which occur early in the prereplicative G1 phase of the cycle, and the transactivating free E2F, which increases in late G1. Here, a regulatory B-myb promoter site was shown to bind with high affinity to free E2F and to E2F-pocket protein complexes in an indistinguishable way in vitro. In contrast, in vivo footprinting with NIH 3T3 cells demonstrated E2F site occupation specifically in early G1, when the B-myb promoter is inactive. These observations indicate that a novel mechanism governs E2F-DNA interactions during the cell cycle and emphasize the relevance of E2F site-directed transcriptional repression.

Cell cycle regulation of cdc25C transcription is mediated by the periodic repression of the glutamine-rich activators NF-Y and Sp1.

The late S/G2-specific transcription of the human cdc25C gene is dependent on an initiator-proximal repressor element (CDE) and an upstream activating sequence (UAS) of undefined nature. We now show that these upstream sequences harbour multiple in vivo protein binding sites that interact with transcriptional activators and form separable, context-independent functional modules. Major components of the UAS are a bona fide Sp1 site and three direct sequence repeats (Yc-boxes). The Yc-boxes interact with the CCAAT-box binding protein NF-Y and are critically dependent on synergistic interactions for efficient transcription activation. The NF-Y complexes, as well as Sp1, are constitutive activators, whose activation function is periodically repressed through the CDE. These observations indicate that the cell cycle regulation of cdc25C transcription is mainly due to the CDE-mediated repression of glutamine-rich activators.

Cell cycle regulation of the cyclin A, cdc25C and cdc2 genes is based on a common mechanism of transcriptional repression.

The S/G2-specific transcription of the human cdc25C gene is due to the periodic occupation of a repressor element ('cell cycle-dependent element'; CDE) located in the region of the basal promoter. Protein binding to the major groove of the CDE in G0 and G1 results in a phase-specific repression of activated transcription. We now show that CDE-mediated repression is also the major principle underlying the periodic transcription of the human cyclin A and cdc2 genes. A single point mutation within the CDE results in a 10- to 20-fold deregulation in G0 and an almost complete loss of cell cycle regulation of all three genes. In addition, the cdc25C, cyclin A and cdc2 genes share an identical 5 bp region ('cell cycle genes homology region'; CHR) starting at an identical position, six nucleotides 3' to the CDE. Strikingly, mutation of the CHR region in each of the three promoters produces the same phenotype as the mutation of the CDE, i.e. a dramatic deregulation in G0. In agreement with these results, in vivo DMS footprinting showed the periodic occupation of the cyclin A CDE in the major groove, and of the CHR in the minor groove. Finally, all three genes bear conspicuous similarities in their upstream activating sequences (UAS). This applies in particular to the presence of NF-Y and Sp1 binding sites which, in the cdc25C gene, have been shown to be the targets of repression through the CDE.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell proliferation and cell cycle progression are not impaired in fibroblasts and ES cells lacking c-Fos.

The transcription factor AP-1 is thought to play an important role in the control of cell proliferation, but the function of individual Fos and Jun family members is a largely unresolved issue. To directly analyse the function of c-Fos in the control of cell proliferation we have used embryonic stem (ES) cells and fibroblasts lacking c-Fos due to a disruption of the c-fos gene by homologous recombination. Our results demonstrate that proliferation of normally cycling cells and reentry of quiescent cells into the cell cycle following serum stimulation are not c-Fos-dependent and occur with similar efficiency in c-fos-/- and control cells. We also show that there is no compensatory overexpression or activation of other known Fos or Jun family members. On the contrary, the c-fos-/- cells showed a reduced induction of fra-1 after serum stimulation which is in agreement with the previous identification of fra-1 as a c-Fos target gene. Comparison of the AP-1 binding and transactivation activities in c-fos-/- and +/+ fibroblasts by electrophoretic mobility antibody supershift and CAT assays suggests that c-Fos is not a major component of AP-1 complexes in these cells. It is therefore conceivable that the lack of any detectable effect on cell proliferation in c-fos-/- cells might be due to a functional redundancy among the different AP-1 family members.

Periodic cdc25C transcription is mediated by a novel cell cycle-regulated repressor element (CDE).

We show that the cell cycle-regulated transcription of the TATA-less cdc25C gene in late S/G2 is largely mediated by a novel promoter element (CDE) located directly 5' to one of the two major transcription initiation sites. Genomic dimethylsulfate footprinting experiments, using either synchronized or sorted normally cycling cells, show the formation in vivo of a CDE-protein complex in both G0 and G1 cells and its dissociation in G2. Mutation of the CDE severely impairs cell cycle regulation of the cdc25C promoter and results in high expression in G0/G1, indicating that the CDE functions as a cell cycle-regulated cis-acting repressor element. Cell cycle regulation is also lost upon removal of the enhancer region located immediately upstream of the CDE, but is largely restored when this enhancerless minimal cdc25C promoter fragment is linked to the constitutive SV40 early enhancer. This indicates that the CDE is dependent on the presence of a transcriptional enhancer to effect cell cycle regulation. Our observations suggest that the periodic activation of the cdc25C gene in late S/G2 is brought about, at least in part, by a unique regulatory mechanism involving the cell cycle-regulated dissociation of a repressor from the CDE.

A novel member of human tissue inhibitor of metalloproteinases (TIMP) gene family is regulated during G1 progression, mitogenic stimulation, differentiation, and senescence.

We have identified in the human diploid fibroblast cell line WI-38 a novel serum-inducible gene, mitogen-inducible gene 5 (mig-5), of the delayed-early class, which represents a new member of the family of human tissue inhibitors of metalloproteinases (TIMPs). The deduced Mig-5 protein shares the highest degree of homology with chicken TIMP-3 (74% identity) and is more distantly related to human TIMP-1 and TIMP-2 (30-38% identity), indicating that mig-5 may represent the human homolog of chicken TIMP-3. In contrast to TIMP-1 and TIMP-2, mig-5 mRNA expression is not only induced in response to mitogenic stimulation but also is subject to cell cycle regulation in normally proliferating WI-38 fibroblasts and HL-60 myeloid cells, showing a clear peak around mid-G1. In agreement with this observation, differentiation of HL-60 cells to either granulocytic or macrophage-like cells leads to increased levels of mig-5 mRNA concomitant with a block in G1. In contrast, mig-5 expression is decreased in senescent human fibroblasts, suggesting that these cells may be blocked at a stage in G1 before or after the phase of maximum mig-5 expression. Since in contrast to the vast majority of other known mitogen-inducible genes, mig-5 expression is periodically up-regulated in G1, this gene should represent an invaluable tool for the analysis of cell cycle progression, terminal differentiation, and replicative senescence.

Inducible acceleration of G1 progression through tetracycline-regulated expression of human cyclin E.

Cyclin E is a cell cycle-regulated protein that activates the cdc2-related protein kinases cdk2 shortly before S-phase entry. In order to analyse the biological role of cyclin E, we have generated HeLa cells that allow the conditional expression of ectopic human cyclin E. In these cells, a cyclin E cDNA is under the control of a bacterial tetracycline repressor-VP16 activator hybrid protein. In the absence of tetracycline, the endogenous gene becomes activated and leads to the synthesis of elevated levels of cyclin E. Concomitant with this increase in cyclin E expression we show by a combined time-lapse video recording/5-bromo-deoxyuridine labelling procedure a significant acceleration of G1 transition by approximately 1.5 hours. This observation is consistent with the idea that cyclin E is a rate-limiting factor with respect to the control of G1-->S transition. The experimental system described here should also prove useful to address the function of cyclin E in further detail.