Monensin-dependent and -independent mechanisms of cell-matrix adhesion.

Attachment and spreading of human FL cells on a subcellular matrix (SCM) preparation made by treating confluent cell monolayers with deoxycholate are insensitive to the presence of monensin. However, if the cell suspension is surface-iodinated prior to adhesion using the LPO/H2O2 system, cell spreading on SCM is inhibited by 1 microM monensin. The suggested interpretation is that cell surface components required for cell spreading on SCM are inactivated by iodination and need replacement from intracellular reserves by a monensin-sensitive pathway. This pathway is not required in the absence of iodination when sufficient surface components (or a monensin-independent pathway of surface expression) are available. Support for this interpretation is obtained by means of double-iodination experiments in which surface-labelled cells adhere and spread, are detached and labelled a second time and then allowed to adhere again to SCM. Cell spreading in the second case is inhibited by approximately 80%, suggesting that both previously expressed and newly recruited receptors are inactivated.