Prolactin activates interferon regulatory factor-1 expression in normal lympho-hemopoietic cells

It has been proposed that prolactin (PRL) is a lympho-hemopoietic growth an d differentiation factor. We show here by Western blotting that PRL-recepto rs (PRL-R) are expressed in normal rat bone marrow and spleen cells. We als o show that PRL stimulates the phosphorylation of the PRL-R-associated Janu s tyrosine kinase (JAK)-2 in rat bone marrow and spleen cells. This leads t o the activation and subsequent binding of signal transducer and activator of transcription (Stat) 5b to an interferon regulatory factor-1 (IRF-1) gam ma activation sequence (GAS) as visualized by electromobility shift assay. As shown after reverse transcription of mRNA by polymerase chain reaction, PRL, at physiological concentrations (0.01 mug/ml), stimulates the expressi on of the IRF-1 gene in these normal cells. PRL could thus affect several a spects of the immune response.