Mesangial cells initiate compensatory tubular cell hypertrophy.

Unilateral nephrectomy results in compensatory renal growth, in which both the size and the functional capacity of the remaining kidney are increased. The functional adaptation to the removal of the contralateral kidney consists mostly of an increase in the glomerular filtration rate of the remaining kidney, and hypertrophy of cells comprising the nephron, mainly of the proximal tubular cells. Although the phenomenon of single kidney hypertrophy has been known for the past thousand years and despite intensive research over the past century, the mechanism of this process still remains unclear. The present article reviews the role of mesangial cells in compensatory renal hypertrophy.

The role of ERK 1/2 and p38 MAP-kinase pathways in taxol-induced apoptosis in human ovarian carcinoma cells.

Taxol is an anticancer agent of natural origin with significant activity against a number of human cancers including ovarian and breast carcinomas. Its cytotoxic activity has been attributed to its ability to stabilize microtubules and to promote microtubule assembly. Recently it has become clearer that Taxol has additional activities including effects in cell signaling and gene expression. We have shown previously that Taxol activates ERK 1/2 MAP-kinases and results in the formation of GRB2/SHC complexes in murine macrophage-like RAW 267.4 cells. Here we demonstrate that Taxol activates ERK 1/2 and p38 MAP-kinases in human ovarian carcinoma cells with distinct kinetics. Activation of ERK1/2 has been observed at low concentrations of Taxol (1-100 nM) within 0.5-6 h, whereas longer exposure(24 h) to nanomolar concentrations of Taxol resulted in an abrogation of the ERK1/2 phosphorylation/activation. Higher concentrations (1-10 microM) resulted in a sharp inhibition of ERK1/2 activity. p38 kinase was activated by high concentrations (1-10 microM) of Taxol within 2 h and remained active for more than 24 h. The kinetic studies showed that these effects of Taxol coincided with an inhibition of proliferation, and the onset of apoptosis. The appearance of the fragmented chromatin visualized by DAPI staining, and DNA fragments seen on an agarose gel, coincided with the decrease in ERK1/2 activation and concomitant increase of the level of active p38 MAPK. The inhibitor PD98059 abrogated ERK 1/2 activation and increased the cytotoxic effect of Taxol. An inhibitor of p38 kinase, SB203580, protected the cells partially from Taxol and, unexpectedly, activated ERK 1/2 kinases. We conclude that the alternative use of ERK1/2 and p38 MAP-kinase pathways may be necessary for the transition from proliferation state to Taxol-induced apoptosisin human ovarian carcinoma cells.

Targeted inactivation of Dp71, the major non-muscle product of the DMD gene: differential activity of the Dp71 promoter during development.

The dystrophin gene, which is defective in Duchenne muscular dystrophy (DMD), also encodes a number of smaller products controlled by internal promoters. Dp71, which consists of the two C-terminal domains of dystrophin, is the most abundant product of the gene in non-muscle tissues and is the major product in adult brain. To study the possible function of Dp71 and its expression during development, we specifically inactivated the expression of Dp71 by replacing its first and unique exon and a part of the concomitant intron with a beta-galactosidase reporter gene. X-Gal staining of Dp71-null mouse embryos and tissues revealed a very stage- and cell type-specific activity of the Dp71 promoter during development and during differentiation of various tissues, including the nervous system, eyes, limb buds, lungs, blood vessels, vibrissae and hair follicles. High activity of the Dp71 promoter often seemed to be associated with morphogenic events and terminal differentiation. In some tissues the activity greatly increased towards birth.

Twist protein in mouse embryogenesis.

The genes in the twist family of bHLH transcription factors are essential for embryogenesis of both vertebrates and invertebrates, as demonstrated by the embryonic lethal phenotypes of the Drosophila and mouse twist-null mutants. Presented here is the embryonic distribution of murine Twist protein (MTwist). Its appearance and presence in the course of early embryogenesis was followed with a monoclonal antibody, alphaTwiMab-1, the first antibody generated against any of the vertebrate Twist proteins. The specificity for MTwist was demonstrated in comparative Western blot experiments, reticulocyte lysate assays, and immunohistochemistry of embryonic mouse samples. Consistent with its probable role as a transcription factor, MTwist localized to the nuclei. MTwist signal first appeared in 8- to 10-somite embryos at 8.25 dpc in the cranial neural crest cells and branchial arches, in the limb-bud mesenchyme and the somatic lateral plate, and in the sclerotome and the dermatome of the somites. The presence of MTwist protein in these tissues corroborates the reported MTwist RNA distribution and the phenotype of the MTwist-null mutants. There also emerged, however, an unexpected difference between MTwist RNA and protein expression. No protein could be detected prior to 8.25 dpc, despite the reported high levels of transcripts as early as 7.0 dpc. Also, the presomitic mesoderm, epithelial somites, and anterior mesoderm expressed abundant MTwist RNA, but no protein. The results suggest posttranscriptional downregulation of MTwist in these regions. A proposed role of MTwist in somite formation and maturation is inhibition of myogenic bHLH and MEF2 genes and thus prevention of premature and/or ectopic differentiation in the presomitic mesoderm and epithelial somites. The absence of MTwist protein from these areas indicates that its role in somitogenesis must be reevaluated.

NK-mediated reduction of malignancy in human melanoma cells treated with theophylline.

Theophylline-treated cells of the human melanoma line showed an increase in NK-sensitivity in vitro and a concomitant decrease in tumorigenicity and spontaneous metastasis in Balb/c nude mice. The MeWo cells were heterogeneous and contained related subpopulations which were cloned to produce two cell lines, one hypodiploid (Cd-16) and one hypotetraploid (Ct-1). Prolonged (3 months) or short-term (4 days) treatment of these cell lines with 1 mM theophylline markedly reduced the incidence and size of tumors in Balb/c nude mice early after s.c. injection and their ability to metastasize spontaneously to the lung was also reduced. The effect was much more pronounced with Cd-16 cells, which contain amplified DNA compared to Ct-1 cells which lack DNA amplification. Part of the tumor inhibition caused by theophylline was due to natural killer (NK) cells. Thus, in vivo treatment of nude mice with anti-asialo GM1, a procedure known to remove NK cells, partially reversed the inhibitory effects of theophylline on tumor formation and generation of metastasis by Cd-16 cells. Consistent with this observation theophylline treatment enhanced the in vitro NK sensitivity of Cd-16 cells four-fold whereas Ct-1 was enhanced only slightly. The data suggest that theophylline can act preferentially on certain tumor cell subpopulations to enhance their NK-sensitive phenotype and thereby inhibit their capacity to form tumors and to metastasize in nude mice.

DNA amplification and metastasis of the human melanoma cell line MeWo.

A positive correlation was found between the presence of amplified DNA in the form of homogeneously staining regions (HSRs), and the formation of spontaneous metastases by the human melanoma cell line MeWo. HSR+ and HSR- MeWo sublines and clones were injected s.c. into BALB/c nude mice. All MeWo lines produced primary tumors that were allowed to grow to a similar size before the animals were sacrificed and examined for the presence of metastatic nodules in the lungs and abdominal cavity. HSR+ lines gave extensive metastases (greater than 100 nodules) in the lungs and/or liver and abdomen in 18 of 19 animals. The HSR- MeWo lines were effectively nonmetastatic, producing metastases in 3 of 20 animals, two of which had only a single metastatic lung nodule each. Evidence for the presence of HSRs in the primary tumors and metastatic nodules was obtained by DNA dot-blot hybridization to a sequence (D15Z1) amplified in the HSRs, flow cytofluorometry for cellular DNA content, and quinacrine staining of metaphase spreads. The HSR+ clones also colonized the lung to a much greater extent than HSR- clones following i.v. injection. In addition, the HSR+ clone had a selective advantage in lung colonization, since i.v. injection of a 50:50 mixture of HSR+ and HSR- clones resulted in extensive metastases populated exclusively by HSR+ cells. The results suggest that DNA sequences amplified in the HSRs of human melanoma MeWo cells may confer enhanced metastatic properties to these cells.