IDENTIFICATION OF THE RECEPTOR FOR A NOVEL M(R)78000 INVASION STIMULATING FACTOR FROM METASTATIC HUMAN PROSTATIC PC-3 ML CLONES

A M(r) 78,000 protein (reduced), termed invasion stimulating factor (I SF), was purified from the conditioned medium of a bone metastasizing human prostatic PC-3 ML clone (M. E. Stearns and M. Stearns. Cancer Me tastasis Rev., 12: 39-52, 1993). Scatchard analysis and affinity cross linking studies revealed that the producer PC-3 hit cells expressed a receptor binding site (M(r) approximate to 115,000). We found a K-d ap proximate to 425 pM and about 22,000 sites/cell. Sodium dodecyl sulfat e-polyacrylamide gel electrophoresis autoradiograms confirmed that the PC-3 ML cells expressed the receptor, whereas the ISF non-producing, noninvasive PC-3 clones (i.e., 3-4 x N.I. PC-3 cells) failed to expres s the ISF receptor. We conclude that a unique ISF autocrine loop chara cterizes the bone metastatic PC-3 ML cells.