Association of 2',5'-oligoadenylate synthetase with the prolactin (PRL) receptor: alteration in PRL-inducible stat1 (signal transducer and activator of transcription 1) signaling to the IRF-1 (interferon-regulatory factor 1) promoter.

The PRL receptor (PRL-R) signals through the Janus tyrosine kinases (JAK) and other non-JAK tyrosine kinases, some of which are preassociated with the PRL-R. To clone PRL-R interacting proteins, the intracellular domain (ICD) of the long form of the PRL-R was used in a yeast two-hybrid screen of a human B cell cDNA library. One PRL-R interacting protein was identified as the 42-kDa form of the enzyme 2',5'-oligoadenylate synthetase (OAS). The in vivo interactions in yeast were further confirmed by an in vitro interaction assay and by coimmunoprecipitation in transfected mammalian cells. Functionally, OAS reduced the basal activity of two types of promoters in transiently transfected COS-1 cells. In the presence of PRL, OAS inhibited PRL induction of the immediate early IRF-1 (interferon-regulatory factor 1) promoter, but not PRL induction of the differentiation-specific beta-casein promoter, suggesting that OAS exerts specific effects on immediate early gene promoters. The inhibitory effects of OAS were accompanied by a reduction in PRL-inducible Stat1 (signal transducer and activator of transcription 1) DNA binding activity at the IRF-1 GAS (interferon-gamma-activated sequence) element. These results demonstrate a novel interaction of OAS with the PRL-R and suggest a role for OAS in modulating Stat1-mediated signaling to an immediate early gene promoter. Although previously characterized as a regulator of ribonuclease (RNase) L antiviral responses, OAS may have additional effects on cytokine receptor signal transduction pathways.

Prolactin receptor expression during adipocyte differentiation of bone marrow stroma.

To determine the role of the hormone prolactin and its receptor on the differentiation, growth, and metabolic activity of cells of bone marrow origin, prolactin receptor expression was assessed in bone marrow stromal cells. Using reverse transcription - polymerase chain reaction, BMS2 cells, a bone marrow stromal cell line, were shown to express prolactin receptors following adipocyte differentiation, using three different adipocyte-differentiation protocols. Primary bone marrow stromal cells also show a dose-dependent increase in prolactin receptor expression following treatment with adipogenic agonists. That prolactin receptor expression is inducible upon adipocyte differentiation was confirmed using a preadipocyte cell line 3T3 - L1. Further, prolactin receptor parallels lipoprotein lipase gene expression in 3T3-L1 cells. These results suggest that prolactin and its receptor may play a role in differentiation and/or metabolism of pre-adipocytes and adipocytes.

Induction of TH1- and TH2-associated cytokine mRNA in mouse bladder following intravesical growth of the murine bladder tumor MB49 and BCG immunotherapy.

Productive immunity to murine and human parasites is associated with the development of a type I T cell response (interferon-gamma-producing) while type II responses (interleukin-4-producing) suppress the development of delayed-type hypersensitivity (DTH) and the elimination of the parasite. To determine if a similar regulatory pathway might exist in tumor systems and may be effected by immunotherapeutic manipulation, we have studied the localized cytokine response to the murine bladder tumor MB49 growing intravesically in syngeneic mice. Intravesical growth of MB49 results in the host-derived expression of mRNA for both interleukin-4 (IL-4) (TH2) and interferon gamma (IFN gamma) (TH1), as well as tumor necrosis factor alpha (TNF alpha) expression of indeterminate origin. Intravesical instillation of bacillus Calmette-Guérin (BCG), highly effective in eliminating bladder tumors clinically and in experimental systems, results in IFN gamma and TNF alpha mRNa production in the bladder wall, but no IL-4. Following BCG treatment of intravesical MB49, the number bladders expressing IL-4 mRNA decreases, while IFN gamma and TNF alpha expression remains constant. These results are consistent with the mechanism of action of BCG involving the generation of an enhanced TH1 immune milieu in the bladder wall, which may contribute to the generation of productive tumor-specific immunity.