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Prolactin and Estrogen Binding in Transplantable Hormone-dependent and Autonomous Rat Mammary Carcinoma¹

Department of Medicine, University of Texas Health Science Center, San Antonio, Texas 78284

A hormone-dependent subline of the transplantable rat mammary tumor MTW9 contains binding sites for both prolactin and estrogen. Prolactin binding is saturable (K_d 2 x 10^-9 M), hormone specific, and destroyed by proteases. By contrast, an autonomous subline derived from the same parent tumor has lost more than 75% of both prolactin- and estrogen-binding sites, although binding affinities for both hormones are unchanged. This reduction in binding sites for both prolactin and estrogen in the autonomous line may result in an incomplete recognition of the tumor cells as a target for the circulating hormones with a subsequent loss of hormone-dependent growth characteristics.

¹ This work was supported in part by National Cancer Institute Grants CA-11378 and CB-23862 and American Cancer Society Grant BC23C.

² Postdoctoral fellow of the Robert A. Welch Foundation.

Received 9/24/74. Accepted 12/30/74.