An evaluation of lysosomal enzyme leakage as a factor influencing the behaviour of transformed cells

Estradiol increases the secretion by MCF7 cells of several lysosomal pro-enzymes

The synthesis and secretion of pro-cathepsin D is increased by estrogens in MCF7 cells. We quantified the effect of estradiol on other lysosomal enzymes in order to investigate the mechanism of this hypersecretion. Precursors of beta-hexosaminidase, cathepsin B and beta-galactosidase, which are routed to lysosomes via the mannose-6-phosphate (Man-6-P) receptor, were secreted in much lower amounts than pro-cathepsin D, but their secretion was also increased by estradiol. The activity of acid phosphatase, which is routed to lysosomes via a different transmembrane mechanism, was not altered by estradiol. While estradiol stimulated gene expression of pro-cathepsin D, it had no effect on that of pro-cathepsin B. We conclude that estradiol stimulates the secretion of several lysosomal pro-enzymes in MCF7 cells, suggesting that a general mechanism is responsible for this derouting rather than a specific alteration of cathepsin D structure.

Stereological analysis of coated pits and secondary lysosomes in cultured human glial and glioma cells

The frequency, distribution and size of coated pits along the upper and lower cell surfaces, and the cytoplasmic volume density of secondary lysosomes were studied by ultrastructural stereological methods in sparse and post-confluent cell cultures of a human normal glial line and a human malignant glioma line. Neither the frequency of coated pits nor the volume density of secondary lysosomes showed any statistically significant changes between the normal glial cells at 2 and 14 days after subcultivation. The numerical surface density of the coated pits was significantly higher along the lower cell surface than on the upper free surface. The coated pits on the malignant glioma cells at 14 days were far more frequent than at 2 days after subcultivation, or than on the sparse and post-confluent glial cells. The surface density of the coated pits was higher along the upper free cell surface than on the lower surface of the glioma cells, in contrast to the glial cells. The volume density of lysosomes was significantly higher in the post-confluent glioma cells than in the sparse cells. The mean diameter of the coated pit openings on cells at 2 days after subcultivation was significantly larger than at 14 days, both in the glial and glioma cell cultures. The observed differences in frequency and distribution of coated pits between the glial and glioma cells may reflect differences in receptor-mediated endocytosis and be related to the different growth characteristics of the normal and malignant cells. The greatly increased load of secondary lysosomes in post-confluent cultures of the glioma cells, in contrast to the glial cells, may be due to a higher rate of autophagocytosis in the malignant cells. The larger size of the coated pit openings on isolated than on post-confluent cells may reflect differences in surface properties between sparse and dense cells.

Cell detachment and metastasis

Cancer cell detachment in three distinct and critical parts of the metastatic cascade is discussed. The detachment of cancer cells from their parent tumors is an initial early event in metastasis. The site of detachment with respect to proximity to blood vessels may determine the initial dissemination route. Many factors affect cell detachment; we specifically consider the effects of growth-rate, necrosis, enzyme activity, and stress on cell release in terms of metastasis-promoting mechanisms. Detachment is also discussed in relation to active cancer cell locomotion, where localized detachment from the substratum is a prerequisite for translatory movement. The importance of active cell movement in tissue invasion has only recently been assessed, and, in the case of at least some human malignant melanomas, a zone of actively moving cancer cells is believed to precede the growing body of the tumor. The secondary release of cancer cells from temporary arrest sites at the vascular endothelium consequent upon intravascular dissemination is also a major area of investigation. Circulating cancer cells arrest at vascular endothelium or are impacted in small vessels, however, most are released into the circulation and subsequently perish. The blood stream is a hostile environment, and it is probable that cancer cells are sufficiently damaged in translocation by hemodynamic trauma and humoral factors such that they easily detach or are 'sheared-off' the vascular endothelium by blood flow. Another possibility is that in some cases they are processed by 'first organ encounters' and perish before or shortly after arriving in a second organ. Animal studies have shown that, following intravenous injection, 60-100% of the injected dose of viable cancer cells are initially arrested in the lungs, but very few remain after 24 hr. As it is only those retained cells which produce tumors, the mechanisms involved in this secondary release, which occurs in all organs so far examined, are critical to any understanding of the metastatic cascade and metastatic inefficiency. The arrest of cancer cells at the vascular endothelium and their subsequent release have been associated with the presence of platelets, and the deposition of fibrin and manipulation of platelet-aggregating mechanisms and fibrinolysis are discussed in terms of their antimetastatic effects. The role of the reticuloendothelial system, natural killer cells, and polymorphs is discussed in relation to cancer cell clearance from blood vessels and also to inherent cancer cell properties which may act to inhibit their metastasis. Although detachment of cancer cells from a primary tumor may be regarded as metastasis promoting, secondary release of cancer cells may be associated with inhibition of metastasis.

Lysosomal hydrolases in long term cultures of human gliomas: total enzyme activities and rate of extracellular accumulation

A number of investigations have suggested a fundamental role for lysosomal enzymes in growth control of normal cells and in the loss of growth control which occurs in neoplasia and in cell cultures transformed by oncogenic viruses. In this investigation total enzyme activities and rates of extracellular accumulation of enzyme were measured in long term cultures of gliomas and normal human astrocytes. Marked differences were found between the cultures with regard to total enzyme activity. Exocytosis rates of the enzymes also showed differences, with one group of tumours demonstrating low or intermediate rates and another smaller group with high rates. There was no positive correlation between the enzyme profile of the cultures and their tumorigenicity in nude mice.

The effects of some aluminium and zirconium compounds on guinea-pig peritoneal macrophages and skin fibroblasts in culture

The damaging effects of some industrially important Aluminium and Zirconium compounds on guinea-pig macrophages and skin fibroblasts have been investigated. Cell death was measured by the release of lactate dehydrogenase activity. The haemolytic properties of these compounds has also been investigated. There is a correlation between the ability of these compounds to form granulomas after intradermal injection in the guinea-pig, their toxic effects on macrophages and fibroblasts and their haemolytic properties. A possible mechanism of toxicity of these compounds towards macrophages and fibroblasts is suggested.

Lysosomal hydrolases of the epidermis. 6. Changes in disease

The activities of 14 acid hydrolases have been measured in normal and diseased human epidermis. Our findings were as follows: (i) Increased hydrolase activity was common in lesions; the clinically uninvolved skin of patients, however, invariably showed normal values. (2) The pattern of change was independent of the nature of the didease, the arylsulphatases and beta-glucosidase usually showing the greatest elevations. (3) The magnitude of the changes differed from disease to disease, being most marked in the lesions of psoriasis. (4) Ichthyosiform erythroderma was exceptional in showing elevated levels of the galactosidases and cathepsins B1 and D. We suggest that (with the exception of ichthyosiform erythroderma) the abnormalities which we have observed may be related to the proliferative rate of the epidermis.

The demonstration of acid phosphatase in cultured 3T3 mouse cells

Acid phosphatase has been demonstrated ultrastructurally in 3T3 and SV40-3T3 mouse cells using sodium beta-glycerophosphate and p-nitrophenyl phosphate as substrate. The former substrate only demonstrates the enzyme in lysosomes and elements of the Golgi apparatus while the latter demonstrates it in the cisternae of the endoplasmic reticulum and in the cell surface as well as at lysosomal sites. The significance of surface acid phosphatase activity is discussed in terms of sublethal autolysis.