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Vol. 279, Issue 6, C2019-C2027, December 2000

Requirement of cortical actin organization for bombesin, endothelin, and EGF receptor internalization

J. Adrian Lunn, Helen Wong, Enrique Rozengurt, and John H. Walsh

Department of Medicine, School of Medicine, Center for Ulcer Research and Education Digestive Diseases Research Center and Molecular Biology Institute, University of California, Los Angeles, California 90095

The role of actin organization in occupancy-induced receptor internalization remains poorly defined. Here we report that treatment of mouse Swiss 3T3 cells with latrunculin A, a potent inhibitor of actin polymerization (including cortical actin), inhibited the internalization of the endogenous bombesin/gastrin-releasing peptide (GRP) receptor, as judged by uptake of ¹²⁵I-labeled GRP or fluorescent Cy3-labeled bombesin. In contrast, cells pretreated with cytochalasin D showed minimal inhibition of bombesin/GRP receptor internalization. Similarly, pretreatment of Swiss 3T3 cells with the potent Rho-kinase inhibitor HA-1077, at concentrations (10-20 µM) that abrogated bombesin-mediated stress fiber formation, did not significantly alter receptor-mediated internalization of ¹²⁵I-GRP. These results indicate that bombesin/GRP receptor internalization depends on latrunculin A-sensitive cortical actin rather than on rapidly turning over actin stress fibers that are disrupted by either cytochalasin D or HA-1077. The rates and total levels of internalization of the endogenously expressed endothelin A receptor and epidermal growth factor receptor were also markedly reduced by latrunculin A in Swiss 3T3 cells. The potency of latrunculin A for inhibiting G protein-coupled receptor endocytosis was comparable to that for reducing internalization of the epidermal growth factor tyrosine kinase receptor. We conclude that cortical actin structures, disrupted by latrunculin A, are necessary for occupancy-induced receptor internalization in animal cells.

signal transduction; heptahelical G protein coupled receptors; growth factor receptors; receptor cell biology; latrunculin; cytochalasin D; Rho kinase; Swiss 3T3 cells; epidermal growth factor; gastrin-releasing peptide

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Deceased 14 June 2000.

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