Studies on Protein Uptake by Isolated Tumor Cells

Abstract

Ferritin, added to the incubation medium of ascites tumor cells, was used as an electron microscopic marker to study the uptake of large protein molecules by morphologically intact cells. A definite uptake could be detected after I hour of incubation in Tyrode bicarbonate solution containing 0.04 to 13.3 mg ferritin/ml. Ferritin was found in a variety of membrane-surrounded structures, suggesting that pinocytcsis and related membrane movements are occurring under physiological conditions and can account for the penetration of intact macromolecules into isolated tumor cells. Supplementation of the medium with serum albumin (33 mg/ml) increased the average amount of ferritin per cell and per pinocytotic structure. Ferritin was strongly adsorbed by fragments of lysed cells, which were readily taken up by intact cells. Besides its role as carrier, this debris appeared to stimulate membrane movements. Only rare examples were found to suggest the release of ferritin from the pinocytotic structures into the cytoplasm. Thus, the disintegration of such structures cannot be considered an obvious step towards a rapid metabolic utilization of protein by the cell. Particles of colloidal gold presented to the cell under the same conditions were not taken up to any significant extent, thus providing good evidence for a selective ingestion of particles of comparable sizes.

Studies on Protein Uptake by Isolated Tumor Cells

“…This vacuolization is considered a common cellular response to a variety of adverse conditions (5) and as an early and at first reversible indicator of cellular injury (3). Furthermore, tumor cells incubated in the presence of ferritin during the occurrence of cell damage develop large peripheral vacuoles containing an appreciable number of marker molecules (42). 4 Similar observations have been made in anoxic liver tissue after injection of colloidal mercury as a marker (38).…”

“…4) which, as we have seen, must be interpreted as a pH artefact due to an increased glycolysis in a medium of high glucose content. The nonphysiological character of the reported nuclear incorporation of DNA (36) also follows from the fact that strong cytoplasmic uptake of ferritin (42) or histones (43) by intact tumor cells is not accompanied by any detectable nuclear localization, whereas marked nuclear staining with fluorescein-labeled histones is seen after exposure of cells to acid media. 2…”

“…However, the uptake process can be distinguished from what usually is called pinocytosis by the following criteria: (a) unlike pinocytosis, it is a pathological response to a variety of unphysiological conditions; (b) the uptake vacuoles are larger in size than pinocytotic vesicles; (c) vacuolization can occur without concurrent increase of pinocytosis. The last characteristic is illustrated by exposures to hypertonic solutions or acid pH, which produce large uptake vacuoles but no apparent increase in the number of pinocytotic vesicles (42). 4 Such morphological differences can be expected to influence the fate of ingested macromolecules in several ways.…”

“…A number of cytochemical and electron microscopic studies from this and other laboratories have demonstrated beyond doubt that protein molecules can be taken up by intact tumor cells in suspension (15,42) and by different normal tissues in vivo (21,23,29,49,50). This uptake occurs by pinocytosis and micropinocytosis and is considered a normal function of living cells.…”

Establishment and Cytological Observation of a Cell Line from Rat Fibrosarcoma Induced by 3-Methylcholanthrene

“…This agrees with Klintworth's data (1969). Data on the nitrogen metabolism of tissue culture cells indicated that proteins of the medium were utilized to an important extent by growing normal and tumor cells (Ryser et al 1962), and that the tumor cells might display a greater uptake of whole proteins than most normal cells (Ryser et al 1962). The metabolic potentials of fibroblastic cells have been found to differ with their malignancy, growing rate or site of origin (Klintworth 1969) and to exert possibly profound effects on the phagocytic capabilities.…”