Involvement of SOCS-1, the suppressor of cytokine signaling, in the prevention of prolactin-responsive gene expression in decidual cells

The cells forming the rat decidua produce PRL and PRL-related proteins and express both the long and short forms of the PRL receptor. Yet, only a defined subpopulation, the mesometrial cells, express the PRL-dependent alpha(2)-macroglobulin gene. This gene is silenced in vivo in the antimesometrial cells and in the CC-AD cell line, derived from antimesometrial cells. To examine whether the lack of alpha(2)-macroglobulin expression is due to defective components in the PRL signaling pathway, we compared the relative expression of Janus kinase 2 (Jak2), signal transducer and activator of transcription 5 a and b (Stat5 a and b), suppressor of cytokine signaling-1 (SOCS-1), and the tyrosine phosphatase SHP-2 mRNA in mesometrial and antimesometrial decidua on days 12 and 13 of pseudopregnancy, the time of maximal alpha(2)-macroglobulin expression. We found no significant differences in the relative expression of either Jak2, State (a and b), or SHP-2 in the two cell populations. However, we discovered a profound difference in the expression of SOCS-1, an inhibitor of the Jak/Stat pathway. This gene was highly expressed in the antimesometrial cells and in the GG-AD cells, which do not produce alpha(2)-macroglobulin. Immunoprecipitation experiments with CC-AD cells revealed that although Jak2 and State coprecipitate in response to PRL stimulation, no phosphorylation of Jak2 and State could be observed. To examine whether SOCS-1 plays a role in silencing the alpha(2)-macroglobulin gene, we cultured CC-AD cells in the presence of either a SOCS-1 antisense oligonucleotide or an irrelevant oligonucleotide for 4, 12, and 28 h. Cells were also treated with PRL. Within 4 h of SOCS-1 antisense treatment, alpha(2)-macroglobulin mRNA expression was initiated. After 28 h, only cells treated with PRL and SOCS-1 antisense oligonucleotide retained the ability to express the alpha(2)-macroglobulin gene. In summary, results of this study reveal that constitutive expression of SOCS-1 can prevent PRL signaling and that the lack of PRL-induced expression of alpha(2)-macroglobulin in a defined decidual cell population is largely due to SOCS-1 expression in these cells.