Department of Obstetrics and Gynecology, New York University School of Medicine, New York, New York 10016, USA
Address for correspondence: Charles J. Lockwood, M.D., Professor and Chairman, Department of Obstetrics and Gynecology, New York University School of Medicine, 550 First Avenue, New York, NY 10016. Voice: 212-263-8579; fax: 212-263-5742.
schatf01{at}popmail.med.nyu.edu
We showed that decidualized stromal cells of luteal phase and
pregnant human endometrium express tissue factor (TF), the primary
initiator of hemostasis, thereby suggesting a mechanism by which
perivascular decidual cells can mitigate the risk of hemorrhage
during endovascular trophoblast invasion. Progestins enhanced
TF mRNA and protein levels in monolayers of human endometrial
stromal cells (HESCs), with estradiol (E
2) + progestin, further
enhancing TF levels despite a lack of response to E
2 alone.
This differential ovarian steroid response has been found for
several decidualization markers. Further studies with cultured
HESCs established that elevated TF levels are mediated by the
progesterone receptor and are maintained for weeks in response
to E
2 plus progestin, thus simulating the chronic upregulation
of TF levels observed in decidualized HESCs
in vivo. Recent
studies revealed that elevated TF expression during
in vitro decidualization of HESCs involved both the EGFR and progesterone
receptor. Thus, enhancement of TF mRNA and protein levels in
the HESCs required co-incubation with a progestin (MPA) and
an EGFR agonist such as EGF or TGF-
. In correspondence with
co-elevation of EGFR and TF in decidualized HESCs in sections
of luteal phase and pregnant endometrium, EGFR levels proved
to be progestin-enhanced in the cultured HESCs. We established
that progestin-enhanced TF expression in HESCs was trancriptionally
regulated, then evaluated the relative roles of SP and EGR-1
sites on the TF promoter in regulating this expression. Transient
transfections with a series of promoter constructs containing
overlapping SP and EGR-1 sites and with constructs in which
the EGR-1 and SP sites were systematically inactivated by site-directed
mutagenesis established the dominance of SP sites in both basal
and progestin-enhanced TF transcriptional activity. Additional
experiments involving transient transfections with SP1overexpressing
vectors and with a specific blocker of if Sp1 binding to its
corresponding GC box specified the importance of the Sp1 transcription
factor. These results were further validated by immunostaining,
which revealed that the ratio of Sp1 to Sp3 increased during
progestin-regulated decidualization of HESCs
in vitro and
in vivo. The absence of canonical estrogen and progesterone response
elements from either the TF or Sp1 gene promoters suggests that
the EGFR may help to mediate progestin-enhanced TF expression
during decidualization of HESCs.
