Expression of transforming growth factor alpha and its messenger ribonucleic acid in human breast cancer: its regulation by estrogen and its possible functional significance

We have studied the estrogenic regulation and the potential autocrine role of transforming growth factor alpha (TGF alpha) in the human breast cancer cell line MCF-7. A biologically active apparent mol wt 30 k TGF alpha was identified by gel filtration chromatography in medium conditioned by MCF-7 breast cancer cells. We previously reported induction of TGF alpha levels in medium by 17 beta-estradiol. We now report correlated increases in TGF alpha mRNA, by Northern and slot blot analysis, after estrogen treatment of MCF-7 cells in vitro. In vivo experiments confirmed these data: estrogen withdrawal from MCF-7 tumor-bearing nude mice resulted in a decline in tumor size and TGF alpha mRNA levels. To explore the functional significance of TGF alpha in MCF-7 cells, anti-TGF alpha antibody was added to MCF-7 soft agar cloning assays. Inhibition of MCF-7 growth resulted, supporting an autocrine role for TGF alpha. Further experiments using an anti-EGF receptor antibody expanded this data, demonstrating inhibition of estrogen-stimulated monolayer MCF-7 cell growth. Examining the generality of TGF alpha expression, 4.8 kilobase TGF alpha mRNAs were seen in three other human breast cancer cell lines, MDA-MB-231, ZR 75B, and T47D. Expression of TGF alpha mRNA was detected in 70% of estrogen receptor positive and negative primary human breast tumors from 40 patients when examined by slot blot and Northern analysis. Thus, we have demonstrated broad expression of TGF alpha in human breast cancer, its hormonal regulation in an estrogen-responsive cell line, and its possible functional significance in MCF-7 cell growth.     

Molecular heterogeneity underlying the G6PD Mediterranean phenotype

Summary As part of a study aiming to define the molecular basis of glucose-6-phosphate dehydrogenase (G6PD) deficiency, we analysed a sample from a Portugese boy with a family history of favism. Although the biochemical properties of red-cell G6PD from this subject were similar to those of the common variant G6PD Mediterranean, the corresponding mutation (563 CT) was not present. Instead, polymerase chain reaction (PCR) amplification and sequencing of the entire gene detected a CT transition at nucleotide 592 in exon VI, changing an arginine residue to a cysteine residue only 10 amino acids downstream from the Mediterranean mutation. Single-strand conformation polymorphism analysis of a PCR-amplified DNA fragment spanning exons VI and VII of the G6PD gene has detected the same mutation, confirmed by sequencing, in a G6PD-deficient patient from Southern Italy. We name this new variant G6PD Coimbra.     

Valinomycin-induced modulation of adriamycin resistance and cationic probe distribution in MCF-7 cell lines.

In vitro restoration of adriamycin sensitivity in a resistant human breast tumor cell line was obtained by continuous exposure to nanomolar nontoxic valinomycin concentrations. Seven-day treatment with nanomolar valinomycin concentrations caused a slight increase of the signal of the cationic fluorescent cyanine probe DiOC5(3) but did not appreciably affect adriamycin incorporation in the cells. A marked increase of the DiOC5(3) signal was obtained in the presence of micromolar valinomycin concentrations, which were incompatible with the in vitro cellular growth.     

The somitogenetic potential of cells in the primitive streak and the tail bud of the organogenesis-stage mouse embryo.

The developmental potency of cells isolated from the primitive streak and the tail bud of 8.5- to 13.5-day-old mouse embryos was examined by analyzing the pattern of tissue colonization after transplanting these cells to the primitive streak of 8.5-day embryos. Cells derived from these progenitor tissues contributed predominantly to tissues of the paraxial and lateral mesoderm. Cells isolated from older embryos could alter their segmental fate and participated in the formation of anterior somites after transplantation to the primitive streak of 8.5-day host embryo. There was, however, a developmental lag in the recruitment of the transplanted cells to the paraxial mesoderm and this lag increased with the extent of mismatch of developmental ages between donor and host embryos. It is postulated that certain forms of cell-cell or cell-matrix interaction are involved in the specification of segmental units and that there may be age-related variations in the interactive capability of the somitic progenitor cells during development. Tail bud mesenchyme isolated from 13.5-day embryos, in which somite formation will shortly cease, was still capable of somite formation after transplantation to 8.5-day embryos. The cessation of somite formation is therefore likely to result from a change in the tissue environment in the tail bud rather than a loss of cellular somitogenetic potency.     

Cobalt blocks the decrease in MEPSP frequency on depolarization in calcium-free hypertonic media

Media made hyperosmotic with sucrose increase the frequency of spontaneously released quanta of transmitter, or miniature excitatory postsynaptic potentials (MEPSPs). In calcium-free medium, depolarization with high potassium reduces the MEPSP frequency, presumably due to calcium efflux in the reversed gradient condition. This effect of depolarization is blocked by cobalt, supporting the above interpretation of the effects of hypertonicity and depolarization and suggesting that cobalt can block efflux as well as influx through calcium channels.     

Evidence for titratable gating charges controlling the voltage dependence of the outer mitochondrial membrane channel,VDAC

Summary A voltage-dependent anion-selective channel, VDAC, is found in outer mitochondrial membranes. VDAC's conductance is known to decrease as the transmembrane voltage is increased in either the positive or negative direction. Charged groups on the channel may be responsible for this voltage dependence by allowing the channel to respond to an applied electric field. If so, then neutralization of these charges would eliminate the voltage dependence. Channels in planar lipid bilayers which behaved normally at pH 6 lost much of their voltage dependence at high pH. Raising the pH reduced the steepness of the voltage dependence and raised the voltage needed to close half the channels. In contrast, the energy difference between the open and closed state in the absence of a field was changed very little by the elevated pH. The groups being titrated had an apparent pK of 10.6. From the pK and chemical modification, lysine epsilon amino groups are the most likely candidates responsible for VDAC's ability to respond to an applied electric field.     

High sensitivity method for fluorofore detection in gradient polyacrylamide slab gels through excitation by laser light: application to glycoproteins stained with concanavalin A-fluorescein isothiocyanate

An easy-to-assemble apparatus for the laser-light excitation of fluorofores in polyacrylamide gels is described. The assemblage is made up of a continuous-wave ion-argon laser with adjustable power output, a beam diffuser, appropriate filters to block excitation light, and a photographic camera. With this setup a minimum 20-fold increase of sensitivity was obtained for fluorofore detection in polyacrylamide gels as compared to the more conventional uv-light excitation using a commercial preparation of Con A-FITC (concanavalin A-fluorescein isothiocyanate) as reference molecule in the gel. The same apparatus, used to analyze the Con A-positive glycoproteins contained in serum Cohn fraction IV separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, showed a number of fluorescent components in a wide range of relative intensities while uv-light excitation showed none. Acrylamide concentration in the gel is critical, since a working limit of between 10 and 12% has been found, above which the diffusion of Con A-FITC in the gel, necessary to label glycoprotein bands, is hampered. The system described here also permits the optimization of detection of minor components not otherwise observable by conventional light excitation, because light power, angle of incidence, and beam divergence can be adapted to analyze specific areas of the sample gel.