Development of desmosomal adhesion between MDCK cells following calcium switching.

The development or maturation of intercellular adhesions following their initiation has received very little attention even though this is an area of significance for a variety of in vivo processes. Using Ca2(+)-induced desmosome formation in MDCK cells as a study system it is shown that, following its initiation, desmosome formation continues for many hours. Following Ca2+ switching the major desmosomal glycoproteins, dg2/3a,b (desmocollins), accumulate progressively at the cell surface. Accumulation is first detectable within 45 min, but continues linearly for approximately 16 h, reaching a plateau at 24-32 h at 15 times the amount present in low-Ca2+ medium (LCM). Desmosomes do not increase in size during this time, but appear to become more numerous. These results suggest that cells progressively increase their desmosome-mediated adhesion over this period of time. Cycloheximide treatment shows that approximately 93% of the total dg2/3a,b accumulation is dependent upon protein synthesis after Ca2+ switching and only approximately 7% on assembly of pre-synthesised material. Thus, although triggering of desmosome formation is rapid, protein synthesis makes a major contribution to the gradual development of desmosomal adhesion in these cells. The initial assembly phase itself can be inhibited by treating cells in LCM with chloroquine, which reduces the cell surface concentration of dg2/3a,b by 40-50%. However, slow dg2/3a,b accumulation does take place in chloroquine and, if protein synthesis is permitted, desmosome formation occurs. It is suggested that when cell contacts are formed in vivo, maximisation of intercellular adhesiveness may take many hours and is dependent on the synthesis and accumulation of adhesive components.