l,25dihydroxyvitamin D3 induces collagen binding to the human monocyte line U937

Interactions of cells with components of the extracellular ma-trix can modulate cellular functions. We measured binding of a major matrix protein to U937 cells, a human promonocytic line. Radioiodinated type I or type III human collagen was bound only to U937 cells differentiated to a more mature phe-notype with 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). Bind-ing was observed at 40C and was saturable; Scatchard analysis of the binding to 1,25-(OH)2D3-pretreated U937 cells indi-cated a single class of high-affinity binding sites. Preincubation of U937 cells with interferon gamma did not induce collagen binding. Collagen binding did not appear to be dependent on fibronectin binding. Surface proteins of U937 cells were 125i labeled and cell membrane proteins resolved by affinity chro-matography on collagen-Sepharose. Major specifically labeled bands of 180, 155, and 125 kD were identified in membrane fractions from 1,25-(OH)2D3-pretreated U937 cells only. 1,25-(OH)2D3 appears to specifically regulate collagen binding to monocyte precursors