Role of laminin-1, collagen IV, and an autocrine factor(s) in regulated secretion by lacrimal acinar cells

Adhesion to novel basement membrane component BM180 in the presence of laminin-1 promotes stimulus-secretion coupling in lacrimal acinar cells [Gt W Laurie, J. D. Glass, R. A. Ogle, C. M. Stone, J. R. Sluss, and L. Chen. Am. J. Physiol. 270 (Cell Physiol. 39): C1743-C1750, 1996]. The identity of the active laminin-1 site and the possibility that other promoters of coupling are present in the acinar cell microenvironment were probed by use of different substrates, media, neutralizing antibodies and cell numbers. Regulated peroxidase secretion was unaffected by basement membrane coat concentration and was detectable at reduced levels in serum-free medium. Anti-laminin-1 antibodies, particularly against sites in the beta 1 and gamma 1 chains, but not al chains, partially suppressed regulated secretion, as did an anticollagen IV antibody. Without effect were RGD peptide and antibodies against entactin, the beta(1)-integrin subunit, and several growth factors. Increasing cell number in serum-free medium revealed an unknown, serum-maskable, secretion-enhancing activity with a remarkable specificity for regulated secretion. Stimulus-secretion coupling, therefore, appears to be modulated by several extracellular factors whose relative contributions remain to be determined.