GALECTIN-3 EXPRESSION AND EFFECTS ON CYST ENLARGEMENT AND TUBULOGENESIS IN KIDNEY EPITHELIAL MDCK CELLS CULTURED IN 3-DIMENSIONAL MATRICES IN-VITRO

Galectin-3 is a member of a closely related family of beta-galactoside -binding soluble proteins found in many vertebrate epithelial and myel oid cell types, The developmentally regulated presence of galectin-3 i n tissues, for example kidney, and an affinity for many cell-surface a nd matrix glycoproteins indicate its importance in extracellular biolo gical processes. Since a polarised expression and secretion of galecti n-3 was observed in monolayer-cultured MDCK cells, an understanding of the secretion and distribution of this lectin in a three-dimensional in vitro model would help to uncover its role(s) in the interplay betw een cell-surface adhesion molecules and extracellular matrix component s occurring during cell aggregation and polarisation in tissue formati on. In this study, the cellular distribution and secretion of galectin -3 were examined in MDCK cells cultured within a gel matrix. MDCK cell s were cultured within type I collagen or Matrigel to obtain multicell ular cysts, and tubule formation was induced in collagen gels with hep atocyte growth factor. Immunofluorescent staining of these structures using antibodies against galectin-3 and other cell-surface domain mark ers was carried out either in situ or on cryosections and was visualis ed by confocal and conventional epifluorescence microscopy. Our result s show that MDCK cells suspended in hydrated collagen gels or Matrigel exhibit differential and polarised galectin-3 expression on the baso- lateral surface domains of cells lining the cysts. The lectin is coloc alised with laminin on the basal surface, In tubule-forming cysts, gal ectin-3 is excluded from the initial spikes and the progressing tips o f the tubules although its basolateral expression on the cyst body rem ains. Galectin-3 added exogenously to cultures, as well as antibodies against laminin subunits and integrin beta(1) subunit, exerted an inhi bitory effect on cyst enlargement of MDCK cells in 3-D Matrigel while galectin-3-specific antibodies could promote this process. The results suggest that galectin-3 exerts its effect on MDCK cells in a three-di mensional environment through modulation of both cell-cell and cell-su bstratum adhesions, and the interplay between these adhesions is impor tant in the growth of multicellular aggregates and extensions occurrin g during normal kidney tubulogenesis.