2. Luman/CREB3 and LRF, novel players in the mammalian unfolded protein response

Expression and localization of Luman RNA and protein during mouse implantation and decidualization

Luman (also known as LZIP and CREB3) is a basic leucine zipper transcription factor of the cAMP response element-binding protein/activating transcription factor gene family. Although Luman had specific roles near termination of Drosophila embryogenesis, the physiological functions of Luman in female mammals have apparently not been reported. Therefore, our objective was to investigate the spatiotemporal expression and regulation of Luman in the mouse uterus during the peri-implantation period. Luman protein was clearly present in the luminal and glandular epithelium on days 1 to 4 of pregnancy (day 1, presence of a vaginal plug) and was observed in decidual cells on day 6 of pregnancy. Expression had progressively increased to day 7 when the second decidual zone was formed. On day 8, apoptosis of the decidualized cells was present, and Luman protein expression was decreased (in close association with decidualization). Luman protein was also present in decidual cells of the artificially decidualized uterus. The expression of Luman was regulated by an activated embryo (according to its expression patterns during pseudopregnancy and delayed implantation). Furthermore, expression of Luman was induced by estrogen in ovariectomized mice. We have concluded that Luman might have important roles in embryo implantation and decidualization.

Luman recruiting factor regulates endoplasmic reticulum stress in mouse ovarian granulosa cell apoptosis

Follicular atresia is primarily induced by granulosa cell apoptosis; however, the molecular mechanisms that control apoptotic cell death in granulosa cells remain poorly understood. The present studies were undertaken to investigate the role of a novel endoplasmic reticulum stress-regulated gene Luman recruiting factor (LRF) in granulosa cell apoptosis during mouse follicular atresia. Based on immunohistochemistry and confocal laser scanning microscope analysis, LRF protein was localized in the cytoplasm of apoptotic granulosa cells, similar to localization of the LRF, Luman, CCAAT/enhancer-binding protein homologous protein and caspase-12 proteins were localized in apoptotic granulosa cells. However, glucose-regulated protein 78 protein was only present in healthy cells of the mural granulosa cell layers. A spontaneous onset of apoptotic cell death of granulosa cells was induced by thapsigargin or tunicamycin treatment in vitro, which was closely related to the increase of LRF, Luman, CCAAT/enhancer-binding protein homologous protein, and caspase-12 mRNA. Taken together, LRF might be involved in inducing apoptosis of granulosa cells through the endoplasmic reticulum stress pathway and might have a key role in mouse follicular selection.