Prolactin receptors in mammary tumors of GR mice.
Prolactin receptors have been identified in estrone-progesterone induced mammary tumors from GR mice. 125I-labeled ovine prolactin binding to tumor homogenates reached a steady state in 12 hours at 22 degrees and was specific for prolactin. Prolactin receptors were highest (16 fmoles/mg protein) in primary, hormone-dependent tumors and declined progressively in transplanted hormone-dependent and transplanted hormone-responsive tumors. In autonomous tumors, binding was approximately 5% of that found in primary tumors. Scatchard analysis of binding to selected tumors indicated that the observed decrease in bound hormone was due to a loss in the number of receptor sites; binding affinity was unaltered (kd approximately 1 X 10(-10) M). Since receptors for estrogen and progesterone as well as those for prolactin decline in a concerted manner with the transition to autonomy, autonomous growth may result from a loss of receptors or an increase in the relative proportion of autonomous cells present in the tumor.
D000818:Animals; D004970:Estrone; D005260:Female; D006168:Guinea Pigs; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000378:metabolism*; D009368:Neoplasm Transplantation; D011374:Progesterone; D011388:Prolactin / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*
D011956:Receptors, Cell Surface; D004970:Estrone; D011374:Progesterone; D011388:Prolactin