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.     

Estrogen-induced lysosomal proteases secreted by breast cancer cells: A role in carcinogenesis?

In an attempt to understand the mechanism by which estrogens stimulate cell proliferation and mammary carcinogenesis, metastatic human breast cancer cell lines (MCF7, ZR75-1) were found to secrete a 52,000 dalton (52K) protein under estrogen stimulation. Following its purification to homogeneity, the 52K protein was identified as a secreted procathepsin-D-like aspartyl protease bearing mannose-6-phosphate signals. This precursor displays an in vitro autocrine mitogenic activity on estrogen-deprived MCF7 cells and is able to degrade basement membrane and proteoglycans following its autoactivation. The total protease (52K + 48K and 34K) was detected and assayed by monoclonal antibodies and was found to be highly concentrated in proliferative and cystic mastopathies. In breast cancer, its cytosolic concentration appears to be correlated more to tumor invasiveness than to hormone responsiveness. The mRNA of the 52K protease accumulates rapidly following estradiol treatment, as was shown by Northern blot analysis with cloned cDNA. The 52K cathepsin-D-like protease is the first example of a lysosomal protease induced by estrogens in cancer cells. Results obtained using different approaches suggest that two cysteinyl cathepsins are also related to cell transformation and invasiveness. It has been proposed that cathepsin-B is involved in breast cancer and metastatic melanoma, and its regulation by estrogen has been shown in the rat uterus. Cathepsin-L corresponds to the major excreted protein (MEP) whose synthesis and secretion are markedly increased by transformation of NIH 3T3 cells with Ki ras and are regulated by several growth factors. In addition to secreted autocrine growth factors and to other proteases (plasminogen activator, collagenase), lysosomal cathepsins may therefore play an important role in the process of tumor growth and invasion as long as their precursor is secreted abundantly.     

Cytogenetic study of F1 hybrids betweenCrepis dinarica andCrepis froelichiana (Asteraceae)

Crepis dinarica andC. froelichiana are two closely related species of theC. praemorsa complex. Even though they exhibit the same chromosome number (2n = 8) and similar idiogram shape, they differ widely in quantity and distribution of heterochromatin bands. The hybrids between these two species comprise three morphological types. Parental genomes were distinguished in hybrids by Giemsa differential staining (C-banding). Although meiosis presents only a few abnormalities (about 2.4%), the percentage of aborted pollen grains is very high (90%).     

Negative control by Sandostatin on pancreatic and duodenal growth: a possible implication of insulin-like growth factor I

This study was undertaken to evaluate the effects of Sandostatin, a potent somatostatin analogue, on pancreatic and intestinal growth and plasma and pancreatic levels of insulin-like growth factor I, a known growth factor. Rats weighing 320-330 g, equipped with an intravenous cannula were infused with either bovine serum albumin or Sandostatin at a dose of 5 micrograms kg-1 h-1 for 7 days. Sandostatin caused significant reductions in pancreatic and intestinal weights accompanied by decreases in total DNA, RNA in both organs and total protein in the intestine while total pancreatic enzymes were increased. Plasma cholecystokinin and insulin-like growth factor I were reduced whereas total insulin-like growth factor I pancreatic content was increased. It is suggested that Sandostatin may reduce growth of these two organs by decreasing cholecystokinin and insulin-like growth factor release and their specific effects at the pancreatic and duodenal cellular level.     

Caerulein and secretin induced pancreatic growth: a possible control by endogenous pancreatic somatostatin

Pancreatic hypertrophy and hyperplasia following chronic joint (CA + SE), or separate, caerulein (CA: 1 microgram . kg-1) and secretin (SE: 75 micrograms . kg-1) administration were studied in parallel with pancreatic somatostatin (SRIF) contents following 2, 4, 7 and 10 days of treatment. Parameters indicative of pancreatic growth (tissue weight, DNA and protein contents, cellular protein concentrations) increased significantly after 2 days of CA or CA + SE and reached a plateau between days 4 and 10. SE merely induced a mild hypertrophy after 4 days. Endogenous pancreatic SRIF contents varied upon treatment, differently so with each peptide regimen. Indeed, CA and CA + SE treatments decreased total SRIF contents after 2 days with no effect thereafter. SE also decreased the latter after 2 days while significant increases were observed after 7 and 10 days. The inverse relationship seemingly existing between SRIF contents and the amplitude of hormonally-induced pancreatic growth supports the hypothesis that endogenous pancreatic SRIF, operating as an 'antigrowth' factor, may participate in the exogenous CA, SE and CA + SE stimulated pancreatic growth phenomena.     

Hemagglutination Inhibition with Arboviruses: Relationship Between Titers and Source of Erythrocytes

Antigens for Grand Arbaud, Hazara, and California arboviruses were able to agglutinate goose and either dog, hamster and guinea pig, or hamster red blood cells (RBC) to the same titer at the same pH; in hemagglutination-inhibition (HI) tests, titers for homologous and related sera were the same with these different types of RBC or occasionally one dilution higher with the mammalian cells. Antigens for St. Louis encephalitis and Eastern equine encephalitis viruses required use of lower antigen dilutions with human, guinea pig, and hamster RBC than with goose RBC. The results of comparative HI testing with these latter antigens and types of RBC indicate that HI titer is not directly related to the antigen dilution used with different types of RBC.