Biomedical subjects

Marie Henriksson

Publications and source records attributed to Marie Henriksson.

6 recordsLinked to original sources

PubMed2003

Intracellular pathways involved in upregulation of vascular endothelin type B receptors in cerebral arteries of the rat.

BACKGROUND AND PURPOSE: Previous studies have shown that contractile endothelin type B (ETB) receptors are upregulated in cerebral arteries after experimental focal cerebral ischemia. The aim of this study was to examine the upregulation of contractile ETB receptors in cerebral arteries after organ culture and to elucidate the intracellular pathways involved. METHODS: Rat middle cerebral arteries (MCAs) were incubated with or without inhibitors. The vessels were mounted in myographs, and the contractile responses to endothelin-1 (ET-1) (ETA and ETB receptor agonist) and sarafotoxin 6c (ETB receptor agonist) were measured. Levels of ETB receptor mRNA were measured with real-time polymerase chain reaction. RESULTS: In fresh MCA, sarafotoxin 6c had no contractile effect. However, after organ culture, a strong concentration-dependent contraction was induced. ET-1 produced a strong contraction, in which the Emax was unaffected by organ culture but the EC50 was decreased with time. The sarafotoxin 6c-induced contraction after 24 hours of organ culture was attenuated by the transcriptional inhibitor actinomycin D and the translational inhibitor cycloheximide as well as the protein kinase C inhibitor Ro-31-8220. Real-time polymerase chain reaction revealed that the mRNA levels of the ETB receptor were increased after organ culture compared with fresh vessels. Actinomycin D and Ro-31-8220 diminished the enhanced mRNA levels considerably. CONCLUSIONS: The results suggest that, in fresh MCA, the ETA receptor is the most prominent subtype, while after organ culture ETB receptors also contribute to the contraction. This upregulation is due to de novo transcription of receptors. Protein kinase C is involved in the upregulation as Ro-31-8220 attenuates the contraction and the mRNA increase.

Animals↗

PubMed2003

Molecular characterization of human telomerase reverse transcriptase-immortalized human fibroblasts by gene expression profiling: activation of the epiregulin gene.

Reconstitution of telomerase activity by ectopic expression of telomerase reverse transcriptase (hTERT) results in an immortal phenotype in various types of normal human cells, including fibroblasts. Despite lack of transformation characteristics, it is unclear whether hTERT-immortalized cells are physiologically and biochemically the same as their normal counterparts. Here, we compared the gene expression profiles of normal and hTERT-immortalized fibroblasts by using a cDNA microarray containing 20,736 cDNA clones and identified 172 dysregulated genes or expressed sequence tags (ESTs). One of the highly expressed genes in the hTERT-immortalized fibroblasts (hTERT-BJ cells) encodes epiregulin, a potent growth factor. Blockade of epiregulin reduced the growth of hTERT-BJ cells and colony formation of hTERT-transformed fibroblasts. Moreover, inhibition of epiregulin function in immortal hTERT-BJ cells triggered a senescence program. Our results suggest that both activation of telomerase and subsequent induction of epiregulin are required for sustained cell proliferation. Given the significant difference in gene expression profiles between normal and hTERT-immortalized fibroblasts and the close relationship between epiregulin and tumorigenesis, we conclude that hTERT-immortalized cells may not replace their normal counterparts for studies of normal cell biology and that the use of hTERT for expansion of normal human cells for therapeutic purposes must be approached with caution.

Cell Division↗

PubMed2003

The Mad and Myc basic domains are functionally equivalent.

The Myc/Max/Mad family of transcription factors plays a fundamental role in the regulation of cell proliferation, oncogenic transformation, and cell differentiation. However, it remains unclear whether different heterodimers, such as Myc/Max and Mad/Max, recognize the same or different target genes in vivo. We show by chromatin immunoprecipitation that Myc target genes are also recognized by Mad1 in differentiated HL60 cells. We also substituted the complete basic region of Myc for the corresponding region of Mad. Wild-type c-Myc was then compared with c-Myc(Mad-BR) in oncogenic transformation, regulation of cell proliferation, induction of apoptosis, activation of chromosomal gene expression, and direct binding to chromosomal sites by chromatin immunoprecipitation. We find that the wild-type c-Myc and c-Myc/MadBR proteins have indistinguishable biological activity and target gene recognition in vivo. These data are consistent with a model in which Myc and Mad regulate a common set of target genes.

Amino Acid Sequence↗

PubMed2002

The histone deacetylase inhibitor trichostatin A derepresses the telomerase reverse transcriptase (hTERT) gene in human cells.

Activation of telomerase, essential for cellular immortalization and transformation, requires the induction of its catalytic component, telomerase reverse transcriptase (hTERT). However, biochemical and genetic mechanisms for the control of hTERT expression remain undefined. In the present study, we demonstrate that the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) induces hyperacetylation of histones at the hTERT proximal promoter, directly transactivates the hTERT gene in normal human telomerase-negative cells, and upregulates hTERT expression in telomerase-positive tumor cells. Overexpression of HDAC1 leads to repression of the hTERT promoter activity. TSA-mediated activation of the hTERT promoter is abolished by the mutation of Sp1 sites at the proximal promoter, suggesting that the effect of TSA is regulated through Sp1 motifs. We also show a physical interaction of Sp1 with HDAC1 and the presence of HDAC1 at the hTERT promoter region. Moreover, hyperacetylation of histones at the hTERT promoter is associated with the natural up-regulation of hTERT expression that occurs in activated T lymphocytes. Taken together, histone acetylation/deacetylation may be a common underlying feature to hTERT transactivation/repression in human normal and malignant cells.

Acetylation↗

PubMed2002

Repression of in vivo growth of Myc/Ras transformed tumor cells by Mad1.

The Myc/Max/Mad network of transcriptional regulatory proteins plays an essential role in cell proliferation, growth, apoptosis, and differentiation. Whereas Myc proteins affect cell cycle progression positively, Mad proteins are negative regulators of cell proliferation. It has been shown in several in vitro systems that Mad proteins antagonize c-Myc functions. In this report we describe the inhibition of tumor cell outgrowth in vivo by Mad1 expression. Transformed cell lines were generated by co-transfection of c-myc, c-H-ras, and a chimeric mad1ER construct into primary rat embryo cells (MRMad1ER cells). Activation of Mad1 by 4-Hydroxy-Tamoxifen (OHT) resulted in abrogation of telomerase activity, reduced cloning efficiency, and decreased proportion of cells in S phase. Injection of MRMad1ER cells into syngenic rats induced aggressively growing tumors after a short latency period. This tumor growth was inhibited by OHT-treatment of animals, with the extent of inhibition correlating with the amount of OHT injected. No effect of OHT on tumor growth was observed with similarly transformed Myc/Ras cell lines which did not express Mad1ER. These data demonstrate that Mad1 is able to suppress Myc/Ras-mediated transformation under in vivo conditions.

Animals↗

PubMed2002

c-myc Suppression in Burkitt's lymphoma cells.

The purpose of the study was to elucidate how DNA tetraplex (also referred to as G-quadruplex)-forming oligonucleotides mediate suppression of the human c-myc gene at the level of transcription initiation. A 22-base-long oligonucleotide, which is rich in guanines and folds into an intrastrand DNA tetraplex under physiological conditions, was administered to a Burkitt's lymphoma cell line overexpressing a (8:14) translocated c-myc allele. Administration of the oligonucleotide at nanomolar concentrations to the surrounding medium resulted in efficient cellular uptake, and was accompanied by a substantial concentration- and conformation-dependent decrease in growth rate. We discuss how c-myc transcription is initiated at the molecular level and speculate that the oligonucleotide exerts a dual effect on c-myc expression in vivo.

Alleles↗