Parathyroid hormone-related peptide (PTHrP) and transforming growth factor-α (TGF-α) were found to stimulate proliferation of human lung cancer cells (BEN-57). TGF-α stimulated PTHrP secretion from these cells. The polyclonal antisera raised against PTHrP significantly inhibited the growth of BEN-57 cells, and also the proliferation induced by TGF-α. Treatment of cells for up to 10 days with either a PTHrP receptor antagonist (PTHrP(7–34)) or PTHrP antiserum significantly inhibited the subsequent growth of these cells. We suggest that PTHrl may be a component of a complex autocrine loop involving TGF-α.
