Objective
To investigate PGRMC1-precipitating proteins in human endometrial stromal cells (ESC) to understand its role during in vitro decidualization. Design: Prospective observational study. Setting: Academic fertility center. Patient(s): Fifteen fertile oocyte donors. Intervention(s): Isolated ESCs decidualized in vitro and used in pulldown assays. Main outcome measure(s): GST-PGRMC1-precipitated proteins identified in nondecidualized ESC (ndESC) and ESC decidualized via a long (8 days) or short (4 days) decidualization protocol (dESC). Result(s): Using pulldown assays and mass spectrometry, decidualization was evaluated by prolactin secretion (ELISA) and cytoskeleton morphology (F-actin staining). The protein interactions were validated by colocalization and coimmunoprecipitation. The pulldown and mass spectrometry analysis identified 21, 24, and 24 new significant GST-PGRMC1-precipitated proteins in ndESC, long dESC, and short dESC, respectively, compared with controls. The functional annotation analysis categorized these proteins mainly into endomembrane system and mitochondria cellular components, both related to adenosine triphosphate (ATP) generation and transport activity, protein biosynthesis and posttranslational processing, vesicle trafficking, and protection against oxidative stress activities. Monoamine oxidase B (MAOB) and B-cell receptor-associated protein 31 (BAP31) were identified in dESC from both decidualization protocols. PGRMC1-MAOB/BAP31 interactions were confirmed by immunofluorescence and coimmunoprecipitation in dESC.