Regulatory action of prolactin on the in vitro growth of CD34+ve human hemopoietic progenitor cells

The pituitary hormone prolactin (Prl) is known to act as a local regulator of immune cell function, and Prl‐binding receptors (Prl‐R) have been described to share distinctive features with the members of the newly described cytokine/hemopoietin receptor superfamily. Here we show that the hormone can functionally interact with lineage‐specific hemopoietic factors. When highly purified progenitor cells (CD34+ve) were seeded in semisolid methylcellulose cultures in the presence of interleukin (IL)‐3, granulocyte‐macrophage colony stimulating factor (GM‐CSF), and erythropoietin (Epo), a selective enhancing effect of Prl on the formation of colony forming unit‐granulocyte (CFU‐G) and burst forming unit‐erythroid (BFU‐E) colonies was observed. The effect of the hormone was plotted as a bell shaped curve, with the optimal response at the supraphysiological concentration of 50 ng/ml. Limiting dilution analysis showed that Prl acted directly on hemopoietic progenitors. This was confirmed by the observation on the CD34+ve cells of Prl‐binding sites reacting with the specific monoclonal antibodies (mAbs), U5 and PrR‐7A. Immunoprecipitation of the metabolically labeled CD34+ve cells with the PrR‐7A mAb revealed a structure of 43 kD under reducing conditions. Analysis of the early events associated with the Prl/Prl‐R interaction showed an increased number of cells engaged in DNA and hemoglobin synthesis. Enhanced erythroid differentiation of CD34+ve cells in the presence of Prl was secondary to upmodulation of receptors for the lineage‐specific factor Epo. Together these data demonstrate the existence of a functional interplay between Prl. and hemopoietic factors. © 1995 Wiley‐Liss, Inc.