Down-regulation of transcription factors AP-1, Sp-1, and NF-kappa B precedes myocyte differentiation

Effects of clotrimazole on the growth, morphological characteristics, and cisplatin sensitivity of human glioblastoma cells in vitro

OBJECT

Clotrimazole, an antimycotic drug, inhibits proliferation of normal and cancer cells by downregulating the movement of intracellular Ca++ and K+. The authors examined the effect of clotrimazole on the growth and sensitivity to cisplatin of two human glioblastoma cell lines--A172, which has the wild-type p53 gene, and T98G, which has the mutant p53 gene in vitro.

METHODS

The A172 and T98G glioblastoma cells were exposed to clotrimazole and cell growth was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium chloride colorimetric assay. Clotrimazole produced a dose-dependent inhibition of cell proliferation and caused changes in cellular structure toward a well-differentiated form. The growth inhibitory effect of clotrimazole was reversible. Western immunoblot analysis revealed a marked increase in cellular glial fibrillary acidic protein and wild-type p53 and a decrease in c-myc and c-fos oncoproteins in both cell lines treated with clotrimazole. Flow cytometric analysis revealed that clotrimazole-treated cells accumulated in the G0/G1 phase with a marked decrease in cells in the S phase; when clotrimazole was washed out from the culture medium, cells again started to proliferate, with a marked decrease in cells in the G0/G1 phase and an increase in cells in the S phase. The growth inhibitory effect of clotrimazole could not be overcome by exogenous stimulation with either epidermal growth factor or c-myc peptide. A combined treatment with clotrimazole and cisplatin significantly enhanced cell cytotoxicity compared with treatment using either drug alone. A DNA fragmentation assay showed that both clotrimazole and cisplatin induced apoptosis, which was increased in cells treated by both drugs.

CONCLUSIONS

The present study indicates that clotrimazole inhibits cell proliferation accompanied by morphological changes toward differentiation of glioblastoma cells and that this drug synergistically enhances the antitumor effect of cisplatin by inducing wild-type p53-mediated apoptosis.

A transient increase in c-myc precedes the transdifferentiation of hepatic stellate cells to myofibroblast-like cells

AIMS/BACKGROUND

Liver stellate cells are transdifferentiated to collagen-producing myofibroblast-like cells in vivo during liver injury or when placed in culture. The purpose of this study was to determine the presence of retinoids and the expression of the immediate early genes as they relate to the transdifferentiation of liver stellate cells in culture.

METHODS

Rat liver stellate cells were studied immediately after isolation or sequentially after culture for varying periods of time. RNA was isolated and specific messages were determined by RT-PCR. Cells were also isolated for determination of retinoid autofluorescence and immunofluorescent staining with specific antibodies by laser confocal microscopy.

RESULTS

c-fos message and immunoprotein were high in the freshly isolated cells prior to culture, while c-myc expression increased markedly after one day of culture. Both c-fos and c-myc gene expression decreased prior to the transdifferentiation of the cells to myofibroblast-like cells and to the increase in alpha 1(I) and alpha 2(I) collagen messages and collagen production. The presence of retinoid autofluorescence and retinoic acid receptor (RAR-alpha and RAR-beta) messages and RAR-beta immunoprotein persisted during initial transdifferentiation of the stellate cells.

CONCLUSIONS

This study shows a high initial level of c-fos expression and a transient increase in c-myc expression followed by a decrease to lower levels prior to transdifferentiation and collagen production by stellate cells. A total loss of retinoid autofluorescence or a decrease in RAR-alpha or RAR-beta are not required for initial transdifferentiation of stellate cells or collagen production.

Vascular cell adhesion molecule-1 gene expression during human smooth muscle cell differentiation is independent of NF-kappaB activation

Vascular cell adhesion molecule-1 (VCAM-1) gene expression in cytokine-activated cells depends on two kappaB elements. Since VCAM-1 expression appears developmentally regulated and cytokine-inducible in smooth muscle cells (SMCs), we have studied the role of NF-kappaB in differentiated SMC VCAM-1 expression. Confluent SMCs were cultured either in a serum-free medium in order to induce differentiation, or in medium with serum, stimulated or not by tumor necrosis factor alpha (TNF-alpha). The expression of smooth muscle myosin heavy chain, a SMC marker, and VCAM-1 was induced concomitantly in serum-free medium, whereas only VCAM-1 expression was induced by cytokine-treatment. We showed that the p50 and p65 subunits of NF-kappaB were localized in the cytoplasm of differentiating SMCs, whereas they were translocated into the nucleus of TNF-alpha-activated SMCs. Electrophoretic mobility shift assays with VCAM-1 gene kappaB elements failed to detect any induction of DNA-protein complex with nuclear extracts of differentiating SMCs in contrast to the cytokine-activated SMC nuclear extracts. Furthermore, VCAM-1 mRNA induction was inhibited in TNF-alpha-stimulated SMCs, but not in differentiating SMCs, by pyrrolidine dithiocarbamate, an inhibitor of NF-kappaB protein activation. Taken together, these findings suggest that in contrast to TNF-alpha activation, NF-kappaB is not involved in VCAM-1 gene expression during SMC differentiation.

Expression of c-myc is down-regulated as mouse mammary epithelial cells become confluent

We have investigated the expression profile of c-myc in the mammary gland. During pregnancy when the gland is actively growing c-myc mRNA was present, while in the differentiated lactating gland no c-myc mRNA was detected. This correspondence between the differentiation state and c-myc mRNA levels in the mouse mammary gland in vivo was paralleled by HC11 mouse mammary epithelial cells in vitro. Firstly, the endogenous c-myc gene was suppressed in confluent compared to growing HC11 cells. In addition, treating the cells with lactogenic hormones did not induce c-myc expression. Secondly, a stably transfected c-myc-CAT reporter construct was similarly down-regulated. Furthermore, using this transfection model, we demonstrate that the mechanism(s) involved in regulating c-myc expression must act through the P1 and P2 core promoter and exon 1. Finally, we demonstrate that suppression of c-myc expression occurs when HC11 cells growth-arrest as they become confluent.