The Effect of Cell-Matrix Interaction on Parathyroid Hormone (PTH) Receptor Binding and PTH Responsiveness in Proximal Renal Tubular Cells and Osteoblast-Like Cells

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Abstract
The interaction of cells with the surrounding extracellular matrix (ECM) or basement membrane (BM) brings about profound changes in cellular biological responses, such as cell differentiation, prolifer- ation, and gene expression. We studied the effect of ECM on PTH receptor binding and on biological responses mediated by PTH, in two cell preparations: 1) the proximal tubular OK opossum kidney cell line; and 2) MC3T3-E1 cells, a clonal line of nontransformed murine osteoblasts. Cells were plated on either plastic surfaces or on tissue culture dishes coated with specific ECM components. In both cell types plated on collagen-type IV (Col-IV), PTH receptor binding, on day 4 of culture, was markedly diminished, when compared with cells on plastic (approximately 45% inhibition, P , 0.01). In addition, Col-IV dose dependently inhibited cAMP generation stimulated by PTH (P , 0.001 vs. plastic), whereas cAMP generation by PGE2, cholera toxin, and forskolin was not altered. In Northern blot anal- ysis, a PTH/PTH-related-protein receptor messenger RNA transcript was detected in both the kidney and bone cells. However, only OK cells manifested a decreased abundance of receptor messenger RNA when plated on Col-IV, compared with plastic. The physiological signifi- cance of inhibited cAMP production by Col-IV was evaluated by mea- suring the influence of different matrices on the activity of Na1/H1 exchanger (NHE) in OK cells and cell mitogenic activity in MC3T3-E1 cells (both responses are negatively modulated by cAMP). OK cells plated on Col-IV showed 70% inhibition of NHE, compared with cells plated on plastic (P , 0.01). PTH inhibits NHE activity in cells on plastic but stimulates exchanger activity by 40% in cells plated on Col-IV. In MC3T3-E1 cells grown on plastic, PTH exerts a dose- dependent antiproliferative effect, which is mediated by cAMP. This effect is mitigated when cells are grown on Col-IV (40 -50% less antiproliferative effect). In summary, Col-IV, a major BM constituent, has a profound inhibitory effect on PTH binding and PTH-mediated biological responses in both kidney tubular cells and osteoblasts. Altered cellular function by Col-IV may be of physiological relevance in states associated with altered composition of BM or expansion of ECM (e.g. diabetes mellitus and interstitial fibrosis). (Endocrinology 139: 3072-3080, 1998)

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