Kurt Engeland

Human Chorionic Gonadotropin Attracts Regulatory T Cells into the Fetal-Maternal Interface during Early Human Pregnancy

Regulatory T cells (Treg) expand during pregnancy and are present at the fetal-maternal interface at very early stages in pregnancy. The migration mechanisms of Treg to the pregnant uterus are still unclear. Human chorionic gonadotropin (hCG) is secreted by the blastocyst immediately after fertilization and has chemoattractant properties. Therefore, we sought to analyze whether hCG secreted by early trophoblasts attracts Treg to the uterus and hence contributes to maternal tolerance toward the fetus. Decidua and placenta tissue samples from patients having spontaneous abortions or ectopic pregnancies were employed to evaluate Treg and hCG levels. Age-matched samples from normal pregnant women served as controls. We further performed in vitro studies with primary first trimester trophoblast cells and a choriocarcinoma cell line (JEG-3) aiming to evaluate the ability of secreted hCG to attract Treg. Patients having miscarriages or ectopic pregnancy presented significantly decreased hCG mRNA and protein levels associated with decreased Foxp3, neuropilin-1, IL-10, and TGF-β mRNA levels as compared with normal pregnant women. Using migration assays we demonstrated that Treg were attracted by hCG-producing trophoblasts or choriocarcinoma cells. Treg migration toward cells transfected with hCG expression vectors confirmed the chemoattractant ability of hCG. Our data clearly show that hCG produced by trophoblasts attracts Treg to the fetal-maternal interface. High hCG levels at very early pregnancy stages ensure Treg to migrate to the site of contact between paternal Ags and maternal immune cells and to orchestrate immune tolerance toward the fetus.

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.

The cyclin B2 promoter depends on NF-Y, a trimer whose CCAAT-binding activity is cell-cycle regulated

Cyclin B2 is a regulator of p34cdc2 kinase, involved in G2/M progression of the cell cycle, whose gene is strictly regulated at the transcriptional level in cycling cells. The mouse promoter was cloned and three conserved CCAAT boxes were found. In this study, we analysed the mechanisms leading to activation of the cyclin B2 CCAAT boxes: a combination of (i) genomic footprinting, (ii) transfections with single, double and triple mutants, (iii) EMSAs with nuclear extracts, antibodies and NF-Y recombinant proteins and (iv) transfections with an NF-YA dominant negative mutant established the positive role of the three CCAAT sequences and proved that NF-Y plays a crucial role in their activation. NF-Y, an ubiquitous trimer containing histone fold subunits, activates several other promoters regulated during the cell cycle. To analyse the levels of NF-Y subunits in the different phases of the cycle, we separated MEL cells by elutriation, obtaining fractions >80% pure. The mRNA and protein levels of the histone-fold containing NF-YB and NF-YC were invariant, whereas the NF-YA protein, but not its mRNA, was maximal in mid-S and decreased in G2/M. EMSA confirmed that the CCAAT-binding activity followed the amount of NF-YA, indicating that this subunit is limiting within the NF-Y complex, and suggesting that post-transcriptional mechanisms regulate NF-YA levels. Our results support a model whereby fine tuning of this activator is important for phase-specific transcription of CCAAT-containing promoters.

Decreased expression of p27 protein is associated with advanced tumor stage in hepatocellular carcinoma

Reduced expression of the cyclin‐dependent kinase inhibitor p27 has previously been correlated with fatal clinical outcome in some tumors, including gastric, breast, and prostate cancers. For hepatocellular carcinoma, the findings are equivocal. In situ hybridization and immunohistochemistry were performed on a series of 203 curatively (R0) resected hepatocellular carcinomas and in corresponding non‐cancerous liver tissue to detect p27. Patients receiving liver transplantation were excluded. The results were correlated with histopathological stage according to the UICC system, Edmondson grade, several other histopathological factors of possible prognostic significance, and finally patient survival. Whereas p27 mRNA was expressed homogeneously in all carcinomas examined, the p27 protein was found in various amounts. The labeling index of p27 protein was significantly lower in advanced stages of the disease (P < 0.001, χ2 = 28.1). We observed decreased p27 protein in higher pT categories (P < 0.001, χ2 = 24.7) and in multiple tumor nodules (P < 0.001, χ2 = 9.3). Multivariate Cox survival analysis identified age, co‐existing cirrhosis, and Edmondson grade as independent prognostic factors. We conclude that evaluation of p27 in hepatocellular carcinoma is useful to predict stage of disease and may have clinical significance, e.g., in predicting optimal therapeutic regimes. Int. J. Cancer 89:350–355, 2000.

The Forkhead Transcription Factor FOXM1 Controls Cell Cycle-Dependent Gene Expression through an Atypical Chromatin Binding Mechanism

ABSTRACT There are nearly 50 forkhead (FOX) transcription factors encoded in the human genome and, due to sharing a common DNA binding domain, they are all thought to bind to similar DNA sequences. It is therefore unclear how these transcription factors are targeted to specific chromatin regions to elicit specific biological effects. Here, we used chromatin immunoprecipitation followed by sequencing (ChIP-seq) to investigate the genome-wide chromatin binding mechanisms used by the forkhead transcription factor FOXM1. In keeping with its previous association with cell cycle control, we demonstrate that FOXM1 binds and regulates a group of genes which are mainly involved in controlling late cell cycle events in the G2 and M phases. However, rather than being recruited through canonical RYAAAYA forkhead binding motifs, FOXM1 binding is directed via CHR (cell cycle genes homology region) elements. FOXM1 binds these elements through protein-protein interactions with the MMB transcriptional activator complex. Thus, we have uncovered a novel and unexpected mode of chromatin binding of a FOX transcription factor that allows it to specifically control cell cycle-dependent gene expression.

Interactions between p300 and Multiple NF-Y Trimers Govern Cyclin B2 Promoter Function

The CCAAT box is one of the most common elements in eukaryotic promoters and is activated by NF-Y, a conserved trimeric transcription factor with histone-like subunits. Usually one CCAAT element is present in promoters at positions between −60 and −100, but an emerging class of promoters harbor multiple NF-Y sites. In the triple CCAAT-containing cyclin B2 cell-cycle promoter, all CCAAT boxes, independently from their NF-Y affinities, are important for function. We investigated the relationships between NF-Y and p300. Chromatin immunoprecipitation analysis found that NF-Y and p300 are bound to the cyclin B2 promoter in vivo and that their binding is regulated during the cell cycle, positively correlating with promoter function. Cotransfection experiments determined that the coactivator acts on all CCAAT boxes and requires a precise spacing between the three elements. We established the order of in vitrobinding of the three NF-Y complexes and find decreasing affinities from the most distal Y1 to the proximal Y3 site. Binding of two or three NF-Y trimers with or without p300 is not cooperative, but association with the Y1 and Y2 sites is extremely stable. p300 favors the binding of NF-Y to the weak Y3 proximal site, provided that a correct distance between the three CCAAT is respected. Our data indicate that the precise spacing of multiple CCAAT boxes is crucial for coactivator function. Transient association to a weak site might be a point of regulation during the cell cycle and a general theme of multiple CCAAT box promoters.

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.

The central role of CDE/CHR promoter elements in the regulation of cell cycle-dependent gene transcription.

The cell cycle‐dependent element (CDE) and the cell cycle genes homology region (CHR) control the transcription of genes with maximum expression in G2 phase and in mitosis. Promoters of these genes are repressed by proteins binding to CDE/CHR elements in G0 and G1 phases. Relief from repression begins in S phase and continues into G2 phase and mitosis. Generally, CDE sites are located four nucleotides upstream of CHR elements in TATA‐less promoters of genes such as Cdc25C, Cdc2 and cyclin A. However, expression of some other genes, such as human cyclin B1 and cyclin B2, has been shown to be controlled only by a CHR lacking a functional CDE. To date, it is not fully understood which proteins bind to and control CDE/CHR‐containing promoters. Recently, components of the DREAM complex were shown to be involved in CDE/CHR‐dependent transcriptional regulation. In addition, the expression of genes regulated by CDE/CHR elements is mostly achieved through CCAAT‐boxes, which bind heterotrimeric NF‐Y proteins as well as the histone acetyltransferase p300. Importantly, many CDE/CHR promoters are downregulated by the tumor suppressor p53. In this review, we define criteria for CDE/CHR‐regulated promoters and propose to distinguish two classes of CDE/CHR‐regulated genes. The regulation through transcription factors potentially binding to the CDE/CHR is discussed, and recently discovered links to central pathways regulated by E2F, the pRB family and p53 are highlighted.

RHAMM is differentially expressed in the cell cycle and downregulated by the tumor suppressor p53

The receptor for hyaluronan-mediated motility RHAMM exerts different functions in the cell as well as on the cell membrane. RHAMM can be exported to the cell surface where it binds hyaluronic acid (HA) and interacts with the HA receptor CD44. Processes like cell motility, wound healing and invasion are modulated by RHAMM. Intracellularly, RHAMM is associated with the cytoskeleton, microtubules, centrosomes and the mitotic spindle. It participates in the control of mitotic spindle stability and integrity. Furthermore, RHAMM is overexpressed in several cancer tissues. We found that RHAMM expression is differentially regulated during the cell cycle and that cell cycle-dependent synthesis of RHAMM is controlled by its promoter on the transcriptional level. RHAMM protein levels follow mRNA expression in the early phases of the cell cycle. However, they already peak in S phase and decrease before the maximum of RHAMM mRNA expression is reached in G2/M. Furthermore, RHAMM expression is downregulated by the tumor suppressor p53. This regulation is observed in a transgenic p53-inducible cell system as well as in cells with wild-type p53 treated with nutlin-3, doxorubicin or paclitaxel. Reporter assays demonstrated that the repression by p53 is regulated on the transcriptional level by the RHAMM promoter also comprising the first exon and the first intron of the gene. In general, our data support a role of RHAMM already in S phase. Additionally, p53-dependent downregulation is consistent with an oncogenic function of RHAMM and the recently reported tumor-suppressive function of CD44 transcriptional repression by p53.

Differential regulation of transcription and induction of programmed cell death by human p53‐family members p63 and p73

The p53 tumor suppressor acts as a transcription factor and has a central function in controlling apoptosis. With p63 and p73 two genes coding for proteins homologous to p53 have been identified. We describe the properties of seven human p63 and p73 proteins as transcriptional activators of p21WAF1/CIP1 expression and apoptotic inducers in direct comparison to p53 in the same assay systems employing DLD‐1‐tet‐off colon cells. Programmed cell death is detected in cells expressing high levels of p53 and p73α. Cells overexpressing TAp63α, TAp63γ, TA*p63α, TA*p63γ, ΔNp63α, and ΔNp63γ display low or no detectable apoptosis.