Background: The composition of the extracellular matrix (ECM) as well as insulinlike growth factor I (IGF-I) receptor density vary along the crypt-villus axis. We determined whether components of the ECM influence IGF-I receptor expression in IEC-18 rat small intestine crypt cells. Methods: IEC-18 cells were cultured on plastic, collagen type IV, Matrigel, and laminin at the plateau and proliferative growth phases. Receptor affinity (Kd) and number (Bmax) were determined by competitive binding of 125I-IGF-I in the presence of increasing concentrations of unlabeled IGF-I. Receptor isolation was performed by affinity cross linking. Messenger RNA (mRNA) for IGF-I receptor was quantified by Northern analysis. Results: Specific binding of IGF-Il>IGF-II>insulin was observed. A 130,000-molecular weight protein was identified by cross-linking, consistent with the a subunit of the IGF-I receptor. Scatchard analysis revealed no effect of ECM on IGF-I binding affinity. In contrast, the Bmax was 18% lower for plateau-phase cells cultured on Matrigel vs. plastic and was 42% lower for cells cultured on laminin vs. collagen type IV. The Bmax for proliferative growth phase cells was decreased when cultured on Matrigel vs. plastic and was 10-fold less than for cells cultured at the plateau growth phase. Northern analysis revealed that IEC-18 cells cultured on Matrigel had less mRNA for IGF-I receptor than cells cultured on plastic. Conclusions: The rate of cell proliferation and the composition of the ECM influence IGF-I receptor expression in IEC-18 cells.
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