Affiliation:
1. Departments of Biochemistry and Obstetrics and Gynecology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-9038
Abstract
ABSTRACT
In the human placental syncytiotrophoblast, C
19
steroids are converted to estrogens by aromatase P450, product of the
CYP19
gene. When human cytotrophoblasts, which lack the capacity to express aromatase, are cultured in 20% O
2
, they spontaneously fuse to form a multinuclear syncytiotrophoblast and
CYP19
expression is markedly induced. On the other hand, when cytotrophoblasts are cultured in 2% O
2
, syncytiotrophoblast differentiation and induction of
CYP19
expression are prevented. We previously observed that expression of the transcription factor Mash-2 (mammalian achaete/scute homologue 2), which is elevated in human cytotrophoblasts and maintained at elevated levels by hypoxia, declines with syncytiotrophoblast differentiation. Overexpression of Mash-2 prevents syncytiotrophoblast differentiation and induction of
CYP19
expression. In the present study, we observed that unexpectedly immunoreactive Mash-2 protein was localized predominately to the cytoplasm of human cytotrophoblasts. Elevated cytoplasmic levels of Mash-2 were maintained when trophoblasts were cultured in 2% O
2
and declined to undetectable levels upon culture in 20% O
2
. Previously, we found that Mash-2 inhibited
CYP19
promoter activity through sequences within a 350-bp region upstream and within placenta-specific exon I.1 containing three E boxes (E1 at −325 bp, 5′-CACTTG-3′; E2 at −58 bp, 5′-CACATG-3′; and E3 at +26 bp, 5′-CACGTG-3′). In this study, we found that trophoblast nuclear protein binding to these E boxes declined with syncytiotrophoblast differentiation in 20% O
2
and was induced by hypoxia; however, Mash-2 did not appear to bind to any of these E boxes. On the other hand, the basic helix-loop-helix leucine zipper transcription factors upstream stimulatory factors 1 and 2 (USF1 and USF2) did bind to E2 and E3 but not E1. Nuclear levels of USF1 and USF2 and DNA-binding activity declined with syncytiotrophoblast differentiation and were maintained at elevated levels by hypoxia and overexpression of Mash-2, whereas USF1 mRNA levels were unaffected. Finally, USF1 overexpression in cultured human trophoblasts markedly inhibited endogenous
CYP19
expression, differentiation of cultured human trophoblast cells, and
CYP19
promoter activity. These findings suggest that increased protein levels and DNA binding of USF1 and USF2 mediate the inhibitory effects of hypoxia and of Mash-2 on
CYP19
gene expression in human placenta.
Publisher
American Society for Microbiology
Subject
Cell Biology,Molecular Biology
Cited by
48 articles.
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