Induction of a reversible G 1 block in human glia-like cells by cytochalasin B

In cultures of normal adult human glia-like cells, density-dependent cell cycle inhibition (topoinhibition) and contact inhibition of ruffling occur almost simultaneously, suggesting a functional coupling between activities of the cell surface and the initiation of DNA synthesis. The present paper examines whether cytochalasin B (CB), which reversibly inhibits ruffling, also blocks the glia cell cycle.The effects of the drug (2 μg/ml) were the following:

1. 1. Initiation of DNA synthesis of subcultivated stationary cells was inhibited.

2. 2. Stimulation of DNA synthesis in stationary cells by medium change was suppressed.

3. 3. Migration of cells into a wound in a confluent cell layer was blocked as well as the initiation of DNA synthesis in cells lining the wound.

4. 4. Initiation (but not continuation) of DNA synthesis of exponentially growing cells was inhibited leading to a population mainly arrested in G 1 as determined by microspectrophotometry on Feulgen-stained cells. Topoinhibited cells were also blocked in G 1. Since cytokinesis was blocked by CB, a fraction of binuclear cells appeared.

The cell cycle block induced by CB was reversible, even after several weeks of treatment, with the exception that binuclear cells more reluctantly entered the S phase after release of the block.In conclusion, CB efficiently induces a reversible and probably physiologic cell cycle block. This finding strengthens the notion of a connection between cell membrane and cell proliferation. The underlying mechanism is discussed.