Regulation and drug insensitivity of f‐actin association with adhesion areas of transformed cells

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Abstract
F‐actin aggregates have been found near the substrate attachments in a variety of transformed cells (Carley et al., 1981). Interference reflection microscopy shows that these aggregates are present in central close adhesion areas in Rous sarcoma virus (RSV)‐transformed rat kidney cells. If these transformed cells are incubated with N6, O2‐dibutyryl 3′:5′‐cyclic monophosphoric acid (db‐cAMP), adenosine (5′‐monophosphoric acid (5′‐cAMP) or adenosine, the F‐actin aggregates and their associated close adhesion areas disappear, and the cells flatten out. Treatment of untransformed cells with db‐cAMP spreads their local adhesion plaques and thickens microfilament bundles. Furthermore, f‐action aggregates are substantially more resistant to cytochalasin B and the Ca2+ ionophore A23187 than microfilament bundles in untrasformed cells. These differences between F‐acttin complexes in untransformed and in RSV‐transformed cells, with respect to morphology and sensitivities to db‐cAMP and cytoskeleton‐disrupting drugs, define properties of the change in F‐actin regulation and association with the plasma membrane due to transformation.