Expression of prolactin and prolactin receptors by non-Hodgkin's lymphoma cells

Prolactin (PRL) interacts with lymphocyte-signaling molecules and cytokines . Previous work has shown independent: and synergistic effects of PRL on th e generation of IL-2-driven anti-tumor lymphokine activated killer (LAK) ac tivity by peripheral blood mononuclear cells (PBMC), The potential importan ce of PRL as a biological immunomodifier, however, is challenged by its abi lity to influence normal lymphocyte mitogenesis and hence lymphoid tumor gr owth. Since non-Hodgkin's lymphoma (NHL) cell lines were efficiently killed by LAK generated with native (n) or recombinant (r) human PRL combined wit h low, per se ineffective doses of IL-2, we have addressed here the questio n of whether PRL acts as a growth factor for LAK targets. NHL cells were an alyzed for: I. expression of the PRL receptor (PRL-R); 2. responsiveness to nPRL or rPRL; 3. constitutive expression and release of PRL; 4. existence of a PRL autocrine loop. PRL-R, defined by multiple antibodies, was detecte d in 3 of IZ NHL cell lines. However, nPRL or rPRL, in a wide range of conc entrations (0.75-50 ng/ml), were not mitogenic for growth-arrested, PRL-R p ositive NHL cell lines. PRL mRNA was detected by RT-PCR in 10 of the 12 cel l lines examined with a higher frequency among AIDS-related NHL cell lines. PRL protein in the immunoprecipitate of S-35-methionine-labeled cell lysat es and supernatants paralleled mRNA expression, and Western blotting analys is showed the presence of the pituitary/lymphocyte non-glycosylated (23.5 k Da) and glycosylated (25 kDa) isoforms. Experiments with blocking antibodie s showed the independence from endogenous PRL for NHL cell growth. (C) 2000 Wiley-Liss, Inc.