Cell substrate adhesion-induced redistribution of proteins among the apical, basal, and internal domains of the plasma membrane of HeLa cells spreading on gelatin.

The establishment of the asymmetric distribution of proteins among the apical, basal, and internal plasma membrane (PM) domains was studied in HeLa cells. Comparisons were made of the amount of membrane and the redistribution of individual PM proteins in the three PM domains for cells on substrates that either induced cell attachment and spreading (gelatin), or induced only attachment (bovine serum albumin (BSA]. Many PM proteins were asymmetrically segregated among the apical, basal, and internal PM domains when cells were attached to gelatin. However, most of the proteins were not totally excluded from any of the domains. In contrast, there was no segregation of membrane components in cells attached to BSA. The segregation of most proteins was well established within 7.5 min of cell attachment when the cells were only partially spread. Cell adhesion induced a change in the movement of total membrane between the internal PM and the external PM domains. When cells attached to either gelatin or BSA there was a transient decrease in the internal PM pool that lasted less than 20 min. For cells attached to BSA the transient decrease was followed by the re-establishment of the internal PM pool which was equivalent to that found in cells in suspension, whereas in cells spreading on gelatin there was only a partial re-establishment of the internal PM pool. Taken together, these observations suggest that the internal PM rapidly moved to the external PM domain during cell adhesion, and that particular PM proteins moved from the internal PM pool into the newly established basal and apical PM domains.