R. Schwimmer et Gk. Ojakian, THE ALPHA-2-BETA-1 INTEGRIN REGULATES COLLAGEN-MEDIATED MDCK EPITHELIAL MEMBRANE REMODELING AND TUBULE FORMATION, Journal of Cell Science, 108, 1995, pp. 2487-2498
Previous studies have demonstrated that incubation of MDCK cell epithe
lial cysts in collagen gel induced a reversal in cell surface polarity
that was regulated by beta 1 integrins. Further experiments were done
to identify the specific collagen binding integrin involved by applyi
ng collagen gel overlays to the apical membrane of subconfluent MDCK m
onolayers. Cell surface levels of the apical membrane glycoprotein gp1
35 were monitored by ELISA to quantitate the extent of collagen-mediat
ed membrane remodeling. After an 8 hour incubation with collagen, ther
e was a 35% reduction in gp135 while the cell surface levels of the al
pha 2, alpha 3 and beta 1 integrin subunits were not affected. Immunof
luorescence microscopy confirmed the loss of gp135 from selected regio
ns of the apical cell surface while the alpha 2 and beta 1 integrin su
bunits were distributed in small clusters over the entire apical membr
ane in both control and collagen-treated monolayers. Collagen-mediated
loss of gp135 was inhibited by monoclonal antibodies which recognize
either the alpha 2 or beta 1 integrin subunits but not by a monoclonal
antibody against the alpha 6 beta 1 integrin. These results demonstra
ted that remodeling of the apical membrane had occurred, allowing the
selective retention of beta 1 integrins but not gp135. They were suppo
rted by the observation that collagen-mediated loss of apical membrane
microvilli was inhibited by the monoclonal antibody against the alpha
2 integrin subunit. Incubation of conflueut monolayers with collagen
gel induced the formation of polarized epithelial tubules within 16 ho
urs, Epithelial tubule biogenesis was completely inhibited by monoclon
al antibodies against either the alpha 2 or beta 1 integrin subunits,
providing strong evidence that the alpha 2 beta 1 integrin is essentia
l for collagen-mediated epithelial membrane remodeling and tubule form
ation.