Differences in affinities between the homologous and the heterologous rabbit prolactin–receptor interaction with respect to proliferation and differentiation activities

• Rec rbPRL was produced in E. coli and characterized in comparison to other lactogens.
• Recombinant and pituitary rbPRLs exhibit similar binding properties and activities.
• RbPRLs exhibit lower binding potency to homologous receptors than that of oPRL.
• RbPRLs have lower proliferation but similar differentiation potency compared to oPRL.

Interspecies differences in PRL–receptor binding and their relationship with bioactivity deserve investigation since cross-reactivity is relevant to the design of many experiments.We have previously shown that the lower affinity of rabbit prolactin (rbPRL) binding to its homologous receptor is due to its faster and more complete dissociation compared with that of ovine PRL (oPRL). In order to obtain sufficient amounts of rbPRL to study the functional consequences of its low affinity homologous interaction, rbPRL was expressed recombinantly in Escherichia coli (rec rbPRL) as insoluble inclusion bodies, refolded and purified to homogeneity, yielding electrophoretically pure, over 98% monomeric rec rbPRL. Proper renaturation of rec rbPRL was evidenced by comparison of its CD spectra, binding parameters and bioactivity with those determined for the rbPRL.The binding potency of rec rbPRL to its receptor, expressed either endogenously in the mammary gland or recombinantly in mammalian cells is one log unit lower than that to the receptor expressed recombinantly in insect cells. This difference is probably related to differences in cell-dependent receptor densities. The proliferation potency of rbPRL or rec rbPRL was one log unit lower than that of oPRL, consistent with its lower binding affinity, but the differentiation potencies of these PRLs were similar.Thus, the proliferation activity is sensitive to PRL–receptor affinity and dissociation kinetics, whereas the differentiation response is marginally modulated.