Objective: Decay-accelerating factor (DAF) is a complement regulatory protein that prevents complement-mediated cell lysis. Its expression in human trophoblasts depends on their anatomic location and gestational age. The mechanisms that govern the regulation of its expression in trophoblasts are not understood. The objective of the present study was to investigate the effects of trophoblast differentiation and cyclic adenosine monophosphate (cAMP) on DAF expression.
Methods: Human trophoblasts were isolated from chorionic villi, cultured, and harvested at timed intervals for total RNA extraction and Northern analysis. Expression of DAF was also assessed by immunocytochemistry. In some cultures, the trophoblasts were exposed to the cAMP agonists 8-bromo-cAMP and Sp-cAMPs or the antagonist Rp-cAMPs.
Results: Expression of DAF mRNA increased as the cells differentiated in culture, with the 2.2-kb transcript of membrane-bound DAF appearing first. As differentiation proceeded, the 1.5-kb transcript became the predominant mRNA form. Exposure of the cells to Rp-cAMPs delayed this process; 8-bromo-cAMP accelerated it. Sp-cAMPs selectively up-regulated the 2.2-kb mRNA transcript. Immunocytochemistry confirmed the effects of differentiation on DAF protein expression.
Conclusion: Expression of DAF in human trophoblasts is dependent on the state of cell differentiation, and cAMP is an intracellular modulator of this process. This effect may be mediated through alternative processing of DAF mRNA in its 3'UT region, which in turn affects mRNA stability.