Dihydrocytochalasin B disorganizes actin cytoarchitecture and inhibits initiation of DNA synthesis in 3T3 cells

Dihydrocytochalasin B (H2CB) disrupts the actin structure of Swiss/3T3 mouse fibroblasts and inhibits the ability of serum growth factors to stimulate DNA synthesis in quiescent cultures. Low doses of H2CB (2-10 X 10(-7) M) added to serum-arrested cells reversibly block initiation of DNA synthesis by serum; by epidermal growth factor and insulin; or by epidermal growth factor, fibroblast growth factor and insulin. H2CB is effective only when added to cells within 8-10 hr after stimulation. Low doses of H2CB cause cell rounding and a loss of actin microfilament bundles, but they do not interfere with glucose or thymidine transport. These results suggest that stimulation of 3T3 cells involves at least one obligatory actin-mediated step. Transformed cells appear to obviate this step, for H2CB does not inhibit the entry into S phase of SV40-transformed or Moloney murine sarcoma virus-transformed 3T3 cells synchronized by mitotic shake-off.