STEROID REGULATION OF ONCOFETAL FIBRONECTIN EXPRESSION IN HUMAN CYTOTROPHOBLASTS

Oncofetal fibronectin (onfFN) is a uniquely glycosylated form of FN su ggested to play a critical role in uterine/placental adherence during pregnancy. In the present study we have examined steroid regulation of onfFN in highly purified preparations (greater-than-or-equal-to 95%) of cytotrophoblasts isolated from human term placentas. Based on immun oassays, relative to controls, treatment of cytotrophoblasts with 10(- 6) M medroxyprogesterone acetate (MPA) down-regulated media levels of onfFN 25, 53, 59, and 62% on days 1, 2, 3 and 4, respectively. The pat tern of steroid regulation and levels of total FN were nearly identica l to that of onfFN suggesting that chronic steroid treatment regulates synthesis of FN and not its oncofetal glycosylation. MPA treatment in duced a 2-fold stimulation in media levels of hCG indicating that incr eased placental function was associated with steroid-mediated changes in FN expression. Steroid specificity experiments demonstrated that MP A, cortisol, and dexamethasone were potent inhibitors of onfFN express ion whereas estradiol (E2), deoxycorticosterone, testosterone, progest erone, and the synthetic progestin OD-14, were not. This suggested tha t glucocorticoids and not progestins may be the physiologic regulators of placental FN expression and that MPA may mediate its matrix-modify ing activity through a glucocorticoid-like mechanism. Treatment of cel ls with dexamethasone (10(-7) M) did not affect the levels of total pr otein synthesis or the release of human placental lactogen to the cult ure medium. This indicated that steroid-mediated down-regulation of on fFN expression in cytotrophoblasts did not result from a general reduc tion of protein synthesis. Based on densitometric scanning of Western blots, MPA and dexamethasone treatments down-regulated media levels of onfFN 70% relative to control levels. Northern blotting revealed that MPA and dexamethasone mediated a 60-90% reduction in steady state lev els of FN mRNA in the presence or absence of E2. Our in vitro model ma y provide a unique system to evaluate steroidal effects on extracellul ar matrix (ECM) protein expression. In addition, we suggest that stero ids may critically regulate placental ECM protein synthesis, and thus affect trophoblast/uterine adherence throughout pregnancy and expulsio n of the placenta and membranes following delivery of the fetus.