Partial purification of a major type of rat prostatic growth factor: characterization as an epidermal growth factor-related mitogen

The dorsolateral prostate of rats contains a mitogen that shares several properties with epidermal growth factor (EGF), which was designated as prostatic EGF-related mitogen (PEM). PEM was purified about 2,100-fold using molecular-sieve and ion-exchange chromatography. Final preparation stimulated DNA synthesis in BALB/c 3T3 cells at a concentration as low as 1.5 ng/ml and competed with 125I-EGF for binding to cell surface receptors. PEM had a molecular weight of about 14,000 and an isoelectric point of about 4.5, being heat- and acid-stable but inactivated by dithiothreitol. The primary cultured rat dorsolateral prostate epithelial cells required EGF for maximum growth. Partially purified PEM fully substituted for EGF in the primary culture system at a concentration as low as 90 ng/ml. However, the activity of PEM was hardly suppressed by antimouse EGF antiserum. These findings suggest that PEM is a member of the EGF family but has a higher molecular weight (high molecular weight EGF).