O2 enhancement of human trophoblast differentiation and hCYP19 (aromatase) gene expression are mediated by proteasomal degradation of USF1 and USF2.
When cultured in 20% O(2), human cytotrophoblasts fuse to form the syncytiotrophoblast with marked induction of hCYP19 (aromatase) gene expression. When cultured in 2% O(2), cytotrophoblast fusion and induced hCYP19 expression are prevented. These effects of hypoxia are mediated by increased expression of mammalian achaete/scute homologue-2 (Mash-2), which increases levels of upstream stimulatory factors 1 and 2 (USF1/2) and their binding as heterodimers to E-boxes surrounding the hCYP19 promoter. In studies to define mechanisms for O(2) regulation of syncytiotrophoblast differentiation, we found that hypoxia and overexpression of Mash-2 markedly increased cyclin B1 levels in cultured trophoblasts and the proportion of cells at the G(2)/M transition. Unlike USF proteins, USF1/2 mRNA levels are unaffected by O(2) tension. To determine whether increased O(2) might enhance proteasomal degradation of USF1/2, human trophoblasts were cultured in 2% or 20% O(2) with or without proteasome inhibitors. In cells cultured in 20% O(2), proteasome inhibitors increased USF1/2 protein levels and blocked spontaneous induction of hCYP19 expression, cell fusion, and differentiation. Like hypoxia, inhibitory effects of proteasome inhibitors on hCYP19 expression were mediated by increased binding of USF1/2 to the E-boxes. In human trophoblast cells cultured in 20% O(2), increased polyubiquitylation of USF1/2 proteins was observed. Thus, early in gestation when the placenta is relatively hypoxic, increased USF1/2 may block trophoblast differentiation and hCYP19 gene expression. In the second trimester, increased O(2) tension promotes proteasomal degradation of USF1/2, resulting in syncytiotrophoblast differentiation and induction of hCYP19 expression.
Jiang
Bing
B
Departments of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, 75390, USA.
Mendelson
Carole R
CR
D001141:Aromatase / Q000235:genetics*; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D002453:Cell Cycle; D002454:Cell Differentiation; D002459:Cell Fusion; D002478:Cells, Cultured; D019926:Cyclin B / Q000235:genetics; D056744:Cyclin B1; D005260:Female; D015870:Gene Expression; D006801:Humans; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism; D066298:In Vitro Techniques; D010100:Oxygen / Q000378:metabolism*; D011247:Pregnancy; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D014327:Trophoblasts / Q000166:cytology* / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
D001141:Aromatase; D051792:Basic Helix-Loop-Helix Proteins; D019926:Cyclin B; D056744:Cyclin B1; D010100:Oxygen; D046988:Proteasome Endopeptidase Complex; D034741:RNA, Small Interfering; D025801:Ubiquitin; C065501:ASCL2 protein, human; C534699:CCNB1 protein, human