Characterization of prolactin receptors in human breast cancer

Summary In order to perform measurement of PRL binding and to improve the knowledge of pathophysiological variations in human mammary cancers, we have investigated in detail the binding characteristics of PRL in membranes prepared from these tumors. The optimization of the assay requires the selection of membranous components of light density (<1.17); the tracer could be either¹²⁵I-PRL after affinity purification on PRL receptors or¹²⁵I-hGH without a purification step. It is favorable to utilize a high amount of protein and 200 000 cpm (2 ng) of tracer. Demonstration of the presence of receptors for PRL with a high affinity (K_d = 3 × 10^–10 M) in breast cancer is presented. The hormonal specificity of these receptors is studied: only lactogenic hormones (hGH, oPRL, hPRL, and hPL) are able to compete for binding of¹²⁵I-hPRL whereas bGH or insulin are without effect. Considering the known effect of PRL on cell multiplication, it is tempting to suggest that this hormone could have a crucial role in the development of breast tumor in humans and that therapies which would suppress secretion of PRL and GH could be beneficial.