Extracellular matrix composition influences insulinlike growth factor I receptor expression in rat IEC-18 cells

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 (K_d) and number (B_max) 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 B_max 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 B_max 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.