Possible involvement of reorganization of actin filaments, induced by tumor‐promoting phorbol esters, in changes in colony shape and enhancement of proliferation of cultured epithelial cells

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Abstract
Tumor promoters are known to induce reorganization of actin, morphological changes and enhancement of proliferation of epidermal cells in vivo. In this study, we have examined the effects of tumor promoters on these events to clarify the role played by the organization of actin filaments in the regulation of the shape and growth of colonies of epithelial cells in culture. Treatment with 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) caused a change in the shape of colonies of FL and Madin‐Darby canine kidney (MDCK) cells within 6 hr. Changes in the shape of colonies were consistent with the morphological change of individual cells and the dissociation of groups of cells in the colonies. Addition of TPA also caused reorganization of actin filaments after 2 hr, and it caused enhancement of proliferation of FL and MDCK cells after 48 hr but did not cause any such changes in KB cells. However, the binding affinities of 4β‐phorbol 12,13‐dibutyrate (PDBu) to FL and MDCK cells were similar to that of PDBu to KB cells. Related tumor promoters such as phorbol 12,13 didecanoate (PDD) and mezerein caused effects similar to those caused by TPA. In contrast, nontumor promoting phorbol esters, such as 4α‐PDD and phorbol, had no effect. Cyclic AMP blocked the TPA‐induced changes in FL and MDCK cells. These results suggest that TPA‐induced reorganization of actin filaments which can be inhibited by cyclic AMP results in changes in the shape of colonies and enhancement of proliferation.

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