J. Cell Sci. 65, 61-72 (1984) 61 Printed in Great Britain © The Company of Biologists Limited 1984 MANGANESE-DEPENDENT CELL-SUBSTRATUM ADHESION FREDERICK GRINNELL Department of Cell Biology, University of Texas Health Science Center, Dallas, Texas 75235, U.SA. SUMMARY I n the presence of manganese, baby hamster kidney cells attached and spread on substrata without added adhesion factors (e.g., fibronectin, lectins). This Mn-dependent adhesion occurred even when the substratum was coated with proteins, such as albumin, haemoglobin, immunoglobulin or ovalbumin, or a dried collagen film. Under similar conditions, cells without Mn in Mg/Ca- containing medium attached poorly and did not spread. Other divalent cations, including Mg, Ca, Fc, Co and Ni, could not replace Mn. Cell surface sites required for Mn-dependent adhesion were destroyed by brief proteolytic treatment of the cells with trypsin or Pronase under conditions where the fibronectin-receptor was unaffected. Also, addition to the incubations of antibodies that in- hibited ligand-mediated cell adhesion (e.g., by fibronectin or lectins) inhibited adhesion of cells in Mn-containing medium and caused rounding of cells previously attached and spread in the presence of Mn. The continuous presence of Mn was required for adhesion. That is, cells that were attached and spread in Mn-containing medium and then switched to Mg/Ca-containing medium (which permitted cytoskeletal function) were found to round up and detach. In marked contrast, cells that were allowed to attach and spread on fibronectin-coated substrata in the presence of Mn did not round up when they were switched to Mg/Ca containing medium. Possible explanations for Mn- dependent cell adhesion are discussed. INTRODUCTION The ligand—receptor model of cell—substratum adhesion is based upon the idea that specific cell surface receptors interact with specific ligands on the substratum (e.g., fibronectin, lectins), and that substrata coated with proteins such as albumin or other materials for which the cells have no receptors are not able to support adhesion (Grinnell, 1978). Some time ago, however, it was shown that Mn was able to promote the attachment and spreading of sarcoma cells in serum-free medium (Rabinovitch & DeStefano, 1973), and a similar observation was later made with baby hamster kidney (BHK) cells (Maroudas, 1975). This result was surprising since BHK cells have generally been found to require specific adhesion factors (i.e., ligands), on the sub- stratum in order for cell spreading to occur. Therefore, the relationship of Mn- dependent adhesion to ligand—receptor mediated adhesion requires explanation. Further work on Mn-dependent adhesion was published recently, and it was proposed that Mn might be an especially effective cofactor for the adhesion- promoting activity of secreted or added fibronectin (Evans & Jones, 1982). This might explain the generally enhanced ability of Mn compared to other divalent cations to promote cell-cell adhesion (Edwards, Campbell, Robson & Vicker, 1975) as well as cell-substratum adhesion (Okada, Takeichi, Yasuda & Ueda, 1974).