Identification of Suppressors of Cytokine Signaling (SOCS) Proteins in Human Gestational Tissues: Differential Regulation Is Associated with the Onset of Labor

Inflammatory cytokines secreted by the placenta and fetal membranes are believed to play an important role in the initiation of parturition. The suppressor of cytokine signaling (SOCS) proteins regulate signal transduction by several cytokines that have been reported to affect gestational tissues. The presence, distribution and roles of SOCS proteins, however, have not been described in human gestational tissues. Using reverse transcriptase (RT)-PCR and Western blot analysis we investigated the expression of SOCS1, SOCS2, and SOCS3 mRNA and protein, respectively, by human villous placenta, amnion and choriodecidua (n = 3-4). Tissues were obtained from uncomplicated pregnancies at term after either spontaneous labor and vaginal delivery or caesarean section (before labor). Messenger RNAs for SOCS1, SOCS2, and SOCS3 were expressed in all tissue types, irrespective of labor status. SOCS proteins were, however, only detectable in villous placenta and in one case in the choriodecidua. Labor was associated with abrogated expression of SOCS1 and SOCS3 proteins in villous placenta and the choriodecidua sample. Following labor the band for SOCS2 protein increased slightly in size which may indicate post-translational modification of SOCS2. Reduced expression of SOCS proteins in gestational tissues may provide a mechanism by which inflammatory cytokines enter into a positive feedback loop of inflammatory changes leading to delivery.