CYTOCHALASIN-INDUCED ACTIN DISRUPTION OF POLARIZED ENTEROCYTES CAN AUGMENT INTERNALIZATION OF BACTERIA

Cytochalasin-induced actin disruption has often been associated with d ecreased bacterial internalization by cultured epithelial cells, altho ugh polarized enterocytes have not been systematically studied. In ass ays using confluent polarized HT-29 enterocytes, cytochalasin D appear ed to increase internalization of wild-type Salmonella typhimurium, Pr oteus mirabilis, and Escherichia coli. HeLa and HEp-2 epithelial cells , as well as HT-29 and Caco-2 enterocytes, were used to clarify this u nexpected observation. Resulting data showed that cytochalasin D was a ssociated with increased internalization of S. typhimurium and P. mira bilis by both HT-29 and Caco-2 enterocytes and,vith increased internal ization of E. coli by HT-29 enterocytes; with either HeLa or HEp-2 cel ls, cytochalasin was associated,vith no change or a decrease in intern alization of these same bacterial strains. Cytochalasin caused decreas ed internalization of listeria monocytogenes by HT-29, Caco-2, HeLa, a nd HEp-2 cells, indicating that cytochalasin did not consistently augm ent bacterial internalization by polarized enterocytes. Fluorescein-la beled phalloidin confirmed marked disruption of filamentous actin in c ytochalasin-treated HT-29, Caco-2, HeLa, and HEp-2 cells. Cytochalasin had no noticeable effect on epithelial viability but caused distorted apical microvilli, cell rounding, and separation of adjacent enterocy tes in confluent cultures (with a corresponding decrease in transepith elial electrical resistance). Scanning electron microscopy showed that cytochalasin-induced enhanced bacterial internalization was associate d with preferential bacterial adherence on the exposed enterocyte late ral surface. Colchicine, used to disrupt microtubules, had no noticeab le effect on bacterial internalization by HT-29 or Caco-2 enterocytes. These data indicated that for HT-29 and Caco-2 enterocytes, cytochala sin-induced disruption of filamentous actin might augment internalizat ion of some bacterial species by a mechanism that appeared to involve exposure of the enterocyte lateral surface.