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C Rechtoris

Publications and source records attributed to C Rechtoris.

8 recordsLinked to original sources
PubMed1995

Isoform-specific induction of the low-density lipoprotein receptor gene by platelet-derived growth factor.

We investigated the effect of recombinant platelet-derived growth factor (PDGF) isomers on low-density lipoprotein (LDL) receptor gene expression and compared this with two indexes of cell growth response: expression of the immediate early gene c-myc and the rate of DNA synthesis. In human skin fibroblasts and NIH 3T3 cells, the PDGF-BB homodimer was more effective in inducing the LDL receptor gene and cell growth response compared with the PDGF-AA homodimer. The second messenger pathways utilized by PDGF receptors for enhancing LDL receptor gene response could, however, be dissociated from those utilized for enhancing c-myc gene response and were insensitive to inhibitors of tyrosine phosphorylation. Inhibition of tyrosine kinase activity inhibited c-myc gene response to PDGF-BB at 10(-8) M but had little effect on LDL receptor gene response. Such inhibition increased expression of the LDL receptor gene in the presence of the PDGF-AA isomer. Our results indicate that the response of the LDL receptor gene to PDGF isoforms reflects cellular growth response. However, different transduction pathways are utilized for PDGF activation of the c-myc and LDL receptor genes in mesenchymal cells.

3T3 Cells↗
PubMed1995

Platelet-derived growth factor enhances Sp1 binding to the LDL receptor gene.

We have previously demonstrated that growth activation of quiescent cells enhances LDL receptor gene transcription and that the proximal 5' flanking region of the LDL receptor gene could transduce a platelet-derived growth factor (PDGF) response. This portion of the LDL receptor gene encompasses a previously characterized sterol response element and an adjacent Sp1 binding site. By use of mobility shift analyses we show that PDGF activation of quiescent cells enhances binding of Sp1 to the LDL receptor gene. Transfection analyses indicated that the Sp1 site, but not the sterol response element binding protein site, could confer PDGF responsiveness to a heterologous promoter in quiescent cells. Furthermore, cotransfection of an LDL receptor reporter gene (containing -141 to +35 bp of the LDL receptor gene promoter) along with an expression construct coding for high-level constitutive expression of an Sp1 cDNA led to marked enhancement in expression of the LDL receptor reporter gene in quiescent cells. Increased Sp1 binding due to PDGF could be due to enhanced production of Sp1; alternatively, posttranslational activation of binding could be involved. Western blot analysis showed no difference in Sp1 abundance in quiescent cells versus PDGF-stimulated cells, suggesting a posttranslational mechanism for activation of Sp1 binding by growth induction. Our data demonstrate that PDGF stimulation of quiescent cells leads to enhanced Sp1 binding to the LDL receptor gene. This enhanced binding could participate in PDGF induction of LDL receptor gene transcription.

3T3 Cells↗
PubMed1994

Evaluation of the role of Ap1-like proteins in the enhanced apolipoprotein E gene transcription accompanying phorbol ester induced macrophage differentiation.

Differentiation of THP1 monocytes to a macrophage phenotype is accompanied by increased apolipoprotein E gene transcription. Using transfection analysis with 5' deletion mutations of the 5' control region of the apo E gene in THP1 cells, we show that the -651 to +86 chloramphenicol acetyltransferase (CAT) construct is efficiently expressed in the monocyte; as has been reported for other cell types. Further, we found that an 176 bp region between -623 to -447 was required for the induction of apolipoprotein E gene transcription during 12-O-tetradecanoylphorbol-13-acetate-induced differentiation of monocytes to macrophages. Gel-retardation patterns of the apolipoprotein E promoter region using nuclear extracts from differentiated or undifferentiated THP1 cells revealed altered binding of Ap1-like nuclear factor/s to the -620 to -583 bp region after macrophage differentiation. Mutation of an Ap1 element at position -602 abolished specific binding of Ap1-like proteins to the -620 to -583 bp fragment of the apo E gene and significantly reduced expression of a -623 to +86 apo E-CAT construct during differentiation. These data indicate that differentiation-related expression of the apolipoprotein E gene following phorbol ester stimulation is transduced by gene elements between -623 and -447. Furthermore, the data indicate that transcriptional activation of the apo E gene during macrophage differentiation is associated with induction of Ap1-like proteins which bind to the Ap1 response element present at -602 in the apolipoprotein E gene and importantly contribute to enhanced gene expression.

Adaptor Protein Complex 1↗
PubMed1992

Transcriptional and post-transcriptional control of apolipoprotein E gene expression in differentiating human monocytes.

The present studies examined the mechanisms responsible for the regulation of apolipoprotein (apo) E gene expression during human monocytic differentiation. Levels of apoE mRNA were low in undifferentiated THP1 cells, a human monocytic cell line. Addition of 12-O-tetradecanylphorbol-13-acetate (PMA) induced differentiation of these cells to a macrophage-like phenotype and was associated with increased apoE mRNA abundance in a time-dependent fashion, up to 10-11-fold within 32 h. Results of nuclear run-on transcription assays demonstrated that the apoE gene was transcriptionally active in undifferentiated THP1 cells and that differentiation of monocytes with PMA was associated with a maximal increase of apoE gene transcription rate of only 2-3-fold at 6-12 h. Using actinomycin D as an inhibitor of new transcription, we could demonstrate a more rapid degradation of mature apoE mRNA in undifferentiated compared to differentiated cells, suggesting that the apoE mRNA species was more stable in differentiated THP1 cells. Primer extension assays performed using RNA extracts from undifferentiated and differentiated THP1 cells confirmed the increase of apoE mRNA abundance in the latter but failed to disclose heterogeneity in apoE gene transcription start site between these two phenotypes. These findings indicate that apoE gene expression is controlled at both transcriptional and post-transcriptional loci during human monocyte-macrophage differentiation.

Apolipoproteins E↗
PubMed1976

A cytotoxic substance in insect cell culture spent media.

Spent media from five different insect cell lines when inoculated into Trichoplusia ni (TN-368) cultures produced cytotoxicity resulting in rounding and detachment of cells. The substance in spent medium from the established cellline Carpocapsa pomonella (CP-169) is believed to be a toxin, based on the failure to serially passage the agent, the early appearance of the cytotoxic effect, and the inability to detect microbes by culturing techniques as well as by electron microscopy. The ability to extract the toxic substance from CP-169 cells indicates that it is cell associated. Biophysical and biochemical properties of the CP-169 cytotoxin are presented.

Cell Line↗
PubMed1976

Polygalacturonases Release Cell-Wall-bound Proteins.

Purified polygalacturonases from two fungi released proteins from wall fractions prepared from three plant species. Peroxidase activity was associated with the proteins released from the cell walls, and several of the protein fractions released contained hydroxyproline. Cellulase, purified free of pectic enzyme activity, was ineffective in releasing cell wall proteins. Specific inhibition of endopolygalacturonase activity prevented release of the proteins.

Journal Article↗