Phosphorylation, glycosylation, and proteolytic activity of the 52-kD estrogen-induced protein secreted by MCF7 cells

We have studied the posttranslational modifications of the 52-kD protein, an estrogen-regulated autocrine mitogen secreted by several human breast cancer cells in culture (Westley, B., and H. Rochefort, 1980, Cell, 20:353-362). The secreted 52-kD protein was found to be phosphorylated mostly (94%) on high-mannose N-linked oligosaccharide chains, and mannose-6-phosphate signals were identified. The phosphate signal was totally removed by alkaline phosphatase hydrolysis. The secreted 52-kD protein was partly taken up by MCF7 cells via mannose-6-phosphate receptors and processed into 48- and 34-kD protein moieties as with lysosomal hydrolases. By electron microscopy, immunoperoxidase staining revealed most of the reactive proteins in lysosomes. After complete purification by immunoaffinity chromatography, we identified both the secreted 52-kD protein and its processed cellular forms as aspartic and acidic proteinases specifically inhibited by pepstatin. The 52-kD protease is secreted in breast cancer cells under its inactive proenzyme form, which can be autoactivated at acidic pH with a slight decrease of molecular mass. The enzyme of breast cancer cells, when compared with cathepsin D(s) of normal tissue, was found to be similar in molecular weight, enzymatic activities (inhibitors, substrates, specific activities), and immunoreactivity. However, the 52-kD protein and its cellular processed forms of breast cancer cells were totally sensitive to endo-beta-N-acetylglucosaminidase H (Endo H), whereas several cellular cathepsin D(s) of normal tissue were partially Endo H-resistant. This difference, in addition to others concerning tissue distribution, mitogenic activity and hormonal regulation, strongly suggests that the 52-kD cathepsin D-like enzyme of breast cancer cells is different from previously described cathepsin D(s). The 52-kD estrogen-induced lysosomal proteinase may have important functions in facilitating the mammary cancer cells to proliferate, migrate, and metastasize.     

Progestin-induced fatty acid synthetase in human mammary tumors: from molecular to clinical studies.

Fatty acid synthetase (FAS) is one of the first well-characterized progestin-induced proteins with available antibodies and cDNA. This paper reviews basic studies on FAS regulation in human breast cancer cell lines and recent data on the possible clinical significance of this new marker of hormone responsiveness in mammary cancer and benign breast diseases.     

Regulation, clinical and biological significance of cathepsin D in breast cancer

The lysosomal protease, pro-cathepsin D, is overexpressed and secreted by human breast cancers. In estrogen-responsive breast cancer cell lines, estrogens and growth factors stimulate cathepsin D expression through distinct mechanisms. Clinical studies indicate that high cathepsin D concentration in primary breast cancers is correlated with an increased risk of metastasis and particularly useful to orientate node-negative tumors towards an adjuvant therapy.     

The influence of plant density on the responses of Sinapis alba to CO2 and windspeed

Plants in nature live in populations of variable density, a characteristic which may influence individual plant responses to the environment. We investigated how the responses of Sinapis alba plants to different wind speeds and CO₂ concentrations could be modified by plant density. In our wind-density experiment the expectation that mechanical and physiological effects of wind will be ameliorated by growing in high density, as a result of positive plant interactions, was realised. Although individual plants were smaller at higher densities, the effect of increasing windspeed was much less than at lower plant densities. A similar reduced sensitivity of individual plant growth under high densities was also observed under CO₂ enrichment. When measured as a population or stand response, there was no effect of density on the CO₂ responses, with all stands showing very similar increases in total biomass with CO₂ enrichment. In the wind speed experiment, total biomass per stand increased significantly with density, although there was no effect of density on the wind speed response. Specific leaf area decreased with increasing wind speed and this response was significantly affected by the density at which the plants grew.     

Close linkage of genes encoding glutamine synthetases I and II in Frankia alni CpI1.

Frankia alni CpI1 has two glutamine synthetases (GSs), GSI and GSII. The GSI gene (glnA) was isolated from a cosmid library of F. alni CpI1 DNA by heterologous probing with glnA from Streptomyces coelicolor. The glnA gene was shown to be located upstream of the GSII gene (glnII) by DNA-DNA hybridization. The nucleotide sequences of the 1,422-bp CpI1 glnA gene and of the 449-bp intervening region between glnA and glnII were determined, and the glnA amino acid sequence was deduced. In common with GSIs from other organisms, CpI1 GSI contains five conserved regions near the active site and a conserved tyrosine at the adenylylation site. F. alni CpI1 glnA complemented the glutamine growth requirement of the Escherichia coli glnA deletion strain YMC11 but only when expressed from an E. coli lac promoter. While the functional significance of maintaining two GSs adjacent to one another remains unclear, this arrangement in F. alni provides support for the recently proposed origin of GSI and GSII as resulting from a gene duplication early in the evolution of life.     

A 250-kilodalton cellular protein is induced by progestins in two human breast cancer cell lines MCF7 and T47D

We have studied the effect of R5020, a synthetic progestin, on the biosynthesis of cellular proteins extracted from the MCF7 and T47D human breast cancer cells, using gel electrophoresis. R5020 stimulates the synthesis, as measured after [35S]-methionine labelling, and the accumulation, as shown by silver staining, of a protein of molecular weight approximately equal to 250,000. The increase of the labelled 250-kilodalton protein was rapid (3 hours) and after 3 days this protein represented approximately equal to 6% of the total cellular proteins (approximately equal to 1 microgram/150,000 cells). The induction of the 250-kilodalton protein was obtained by physiologically active concentrations of several progestins and high concentrations of 5 alpha-dihydrotestosterone but not by estradiol or dexamethasone. It was inhibited by R486 , a progestin antagonist, but not by flutamide, an androgen antagonist. These results indicate a mediation by the progesterone receptor. The 250-kilodalton protein appears to be an excellent probe to study in cell culture the mechanism of action of progestin on human cells.     

Evidence of androgen and estrogen receptors in the preen gland of male ducks

Androgen receptors have been found in duck preen glands by using dextran-coated charcoal adsorption. They bound DHT with high affinity (KD = 0.2 nM), limited capacity (45 fmoles/mgP) and good specificity. They sedimented at 8 S in a sucrose gradient and were destroyed by pronase digestion and heating. An estrogen receptor having different binding specificity was also demonstrated. On the basis of a marked annual cycle of gonadal activity in ducks, this system appears appropriate for studying the regulation of sex steroid hormone receptors.     

Androgen on the estrogen receptor I — Binding and in vivo nuclear translocation

In the immature rat uterus, high concentrations of androgens competed specifically with estradiol on the estrogen receptor (RE). This competition was stereospecific for C₁₉ steroids bearing a 17β and/or 3 hydroxyl group. Very low affinity ligands, such as testosterone, could not compete with estradiol at equilibrium but decreased the association rate of estradiol on its receptor. High doses (> 0.4mg) of 5 α aihydrotestosterone provoked $\text{in vivo}$ as $\text{in vitro}$ the nuclear translocation of RE. The nuclear receptor thus formed displayed the same 5.2 S sedimentation constant as that induced by estradiol. We conclude that the weak affinity binding of androgens to the estrogen receptor is sufficient to induce its nuclear translocation $\text{in vivo}$ provided androgen concentration is high enough in uterus to occupy the estradiol binding site. Conversely, progesterone which does not bind RE could not provoke its nuclear translocation.     

Trophic interactions in a high arctic snow goose colony

We examined the role of trophic interactions in structuringa high arctic tundra community characterized by a large breedingcolony of greater snow geese (Chen caerulescens atlantica).According to the exploitation ecosystem hypothesis of Oksanenet al. (1981), food chains are controlled by top-down interactions.However, because the arctic primary productivity is low, herbivorepopulations are too small to support functional predator populationsand these communities should thus be dominated by the plant/herbivore trophic-level interaction. Since 1990, we have beenmonitoring annual abundance and productivity of geese, the impactof goose grazing, predator abundance (mostly arctic foxes, Alopexlagopus) and the abundance of lemmings, the other significantherbivore in this community, on Bylot Island, Nunavut, Canada.Goose grazing consistently removed a significant proportionof the standing crop (