Submitted on May 31, 2008
Revised on July 22, 2008
Accepted on July 28, 2008
Serotonin Modifies Cytoskeleton and Brush Border Membrane Architecture in Human Intestinal Epithelial Cells
Ravinder K. Gill1*, Le Shen2, Jerrold R. Turner3, Seema Saksena4, Waddah A. Alrefai1, Nitika Pant1, Ali Esmaili, Alka Dwivedi, Krishnamurthy Ramaswamy, and Pradeep K. Dudeja
1 University of Illinois at Chicago
2 University of Chicago
3 The University of Chicago
4 University of Illinois
* To whom correspondence should be addressed. E-mail: rgill{at}uic.edu.
Serotonin or 5-hydroxytryptamine (5-HT) influences numerous functions in the gastrointestinal tract. We previously demonstrated that 5-HT treatment of Caco-2 cells inhibited Na+/H+ exchangers (NHE) and Cl-/OH- exchange activities via distinct signaling mechanisms. Since regulation of several ion transporters such as NHE3 is influenced by intact cytoskeleton, we hypothesized that 5-HT modifies actin cytoskeleton and/or brush border membrane architecture via involvement of signaling pathways. Ultrastructural analysis showed that 5-HT (0.1 µM, 1h) treatment of Caco-2 cells caused the apical membrane to assume a convex dome shape that was associated with shortening of microvilli. To examine whether these cellular architecture changes are cytoskeleton driven, we analyzed actin cytoskeleton by fluorescence microscopy. 5-HT induced basal stress fibers with prominent cortical actin filaments via 5-HT3 and 5-HT4 receptor subtypes. This induction was partially attenuated by chelation of intracellular Ca2+ and PKC
inhibition (Go6976). In vitro assays revealed that PKC interacted with actin and this association was increased by 5-HT. Our data provide novel evidence that 5-HT-induced signaling via 5-HT3/4 receptor subtypes to cause Ca2+ and PKC-dependent regulation of actin cytoskeleton may play an important role in modulation of ion transporters that contribute to pathophysiology of diarrheal conditions associated with elevated levels of 5-HT.
