Employment of synchronized cells and flow microfluorometry in investigations on the JB-1 ascites tumour chalones

Structural and functional significance of association of a low molecular weight chalone from JB-1 ascites tumours with high molecular weight factors

The cell-specific inhibitory (chalone) activity of JB-1 ascites tumour cell proliferation has been purified using five different procedures. By combining (1) molecular weight estimations based on ultrafiltration and gel chromatography, and (2) partitioning in organic solvent and ion exchanges, it is concluded that the active factor associates, in a complex manner, with various other components involving both hydrophobic and ionic forces. The active factor appears to be slightly acidic, hydrophobic peptide (molecular weight 500-1000 D). When assessing the activity in vivo, it appears to be highly dependent on associated serum factors. Thus, the chalone studied appears to interact both structurally and functionally with various associated factors which affect its physicochemical behaviour and biological activity.

A flow cytometric in vivo chalone assay using retransplanted old murine JB-1 ascites tumour cells

A flow cytometric in vivo chalone assay is described. Transplantation of old JB-1 ascites tumour cells to new hosts induced an influx of tumour cells, with G1 DNA content, to the S phase. This induction could be reversibly and specifically blocked by injections of an ultrafiltrate of old JB-1 ascites fluid. The method described is superior to a previously published in vivo chalone assay using regenerating ascites tumours. Owing to a reduced variability in time of onset of DNA synthesis, a smaller scatter of observations is achieved and thus the number of mice per group may be reduced using the new method. In contrast to the older technique, the present one does not necessitate killing of mice during the observation period.

Formation of large vacuoles in tumour cells grown in suspension

In suspension cultures of JB-1-E cells approximately 11% of the cells contained a single large vacuole ("balloon cells") or signet-ring cells). Such cells were rarely observed in monolayer cultures, where the cells were attached to a substrate. Only a few "balloon cells" were observed in suspension cultures of HeLa S3 cells. Both cell lines were able to phagocytize latex particles of 5.7 micrometer mean diameter. Nocodazole significantly reduced the formation of "balloon cells" in suspension cultures of JB-1-E cells. Transmission electron microscopy indicated that various cytoplasmic membrane components probably could contribute to the membrane material of the vacuoles. It is believed that the formation of "balloon cells" is due to changes in the regulation of the cellular membrane material.

Observations on the association of annulate lamellae with vinblastine-induced paracrystals in tumour cells in vitro

Tumour cells in vitro responded to prolonged treatment with colchicine with the formation of annulate lamellae. Following the colchicine treatment, paracrystals were induced with vinblastine. A close association of annulate lamellae with vinblastine-induced crystals was observed. The hypothesis that annulate lamellae and the related unclear membrane with the pore complexes may play a role in the control of the cytoplasmic microtubule complex is discussed.

Specific chalone inhibition of the regeneration of the JB-1 ascites tumour studied by flow microfluorometry

The variation in the DNA distribution in the JB-1 and the Lla2 ascites tumour was investigated by means of flow microfluorometry (FMF) in the plateau stage and during the initiation of the regenerative growth induced by percutaneous aspiration. The study showed that a considerable influx of cells with G1DNA content into the S phase occurred in both tumours about 10 hr after aspiration. In the JB-1 tumour, these initial regenerative changes could be reversibly blocked by injections of cell-free plateau JB-1 ascitic fluid or an ultrafiltrate of this ascites. In contrast to these observations no delay in the regenerative changes was observed in the L1a2 tumour after treatment with JB-1 ascites or the ultrafiltrate. The study supports the assumption of a specific growth regulation of the JB-1 ascites tumour and emphasizes the suitability of FMF analyses in cell-kinetic studies in which short-term fluctuations take place in the distribution of cells with different DNA content.

Characterization of a G1 inhibitor from old JB-1 ascites tumor fluid. Interaction with polyions and ion exchangers

In most experimental ascites tumors the growth rate decreases with increasing age and cell number. This decrease is caused by a prolongation of the cell cycle and an increasing accumulation of noncycling cells in resting (or quiescent) G1 and G2 compartments. In cell-free ascitic fluid from the JB-1 ascites tumor in the plateau phase of growth, low molecular weight substances have been found which reversibly and specifically arrest JB-1 cells in G1 and G2. In order to characterize the JB-1 G1 inhibitor we have investigated the effect of ion exchangers and polyions on the activity of this inhibitor assayed in vitro by means of a partially synchronized JB-1 cell population analyzed by flow microfluorometry. The results indicate that polyanions and cation exchangers (immobilized polyanions) bind and abolish the G1-inhibitory activity. From this it is suggested that the G1 inhibitor is of a basic or polycationic nature. Since anion exchangers (immobilized polycations) are without effect on this activity it was surprising to find that polycations also neutralize the activity. The results indicate that this occurs by blocking an anionic G2-inhibitor receptor on the cell, thus preventing the polycationic G1 inhibitor from being bound to this receptor.