Nuclear accumulation of epidermal growth factor in cultured bovine corneal endothelial and granulosa cells

Intracellular accumulation of intact ¹²⁵I-labeled epidermal growth factor (¹²⁵I-EGF) in corneal or granulosa cell cultures exposed to either chloroquine or leupeptin can be 10-fold higher than that observed in cultures not exposed to the lysosomal inhibitors. This has made it possible to study the translocation and accumulation of ¹²⁵I-EGF in a nuclear fraction of both cell types. The accumulation of ¹²⁵I-EGF was found to be dependent of the inhibitor's concentrations. Chloroquine at a concentration of 5 x 10^-5 M yielded a maximal nuclear accumulation which amounted to 18% of the total ¹²⁵I-EGF present within the bovine corneal endothelial cells exposed to chloroquine. Nuclear accumulation could be detected in that cell type as early as 4 h after cultures were exposed to both chloroquine and ¹²⁵I-EGF and was maximal by 24 hr. Saturation of nuclear accumulation of ¹²⁵I-EGF in corneal endothelial and granulosa cell cultures was observed at 20 and 10 ng/ml of ¹²⁵I-EGF, respectively. After 24 hr , 1.06 x 10⁴ and 1.4 x 10^{4 125}I-EGF molecules were found associated with granulosa or corneal endothelial nuclei, respectively. In corneal endothelial cell cultures exposed to chloroquine, a small fraction (0.6%) of ¹²⁵I-EGF associated with the cell was found to be irreversibly bound to a polypeptide with a molecular weight of 185,000, and 50% of these irreversible ¹²⁵I-EGF receptor complexes were found to be associated with the nuclei.