The c-Myc-Regulated MicroRNA-17∼92 (miR-17∼92) and miR-106a∼363 Clusters Target hCYP19A1 and hGCM1 To Inhibit Human Trophoblast Differentiation

Abstract

cMononuclear cytotrophoblasts of the human placenta proliferate rapidly, subsequently fuse, and differentiate to form multinucleated syncytiotrophoblast with induction of aromatase (hCYP19A1) and chorionic gonadotropin (hCG␤) expression. Using microarray analysis, we identified members of the miR-17ϳ92 cluster and its paralogs, miR-106aϳ363 and miR-106bϳ25, that are significantly downregulated upon syncytiotrophoblast differentiation. Interestingly, miR-19b and miR-106a directly targeted hCYP19A1 expression, while miR-19b also targeted human GCM1 (hGCM1), a transcription factor critical for mouse labyrinthine trophoblast development. Overexpression of these microRNAs (miRNAs) impaired syncytiotrophoblast differentiation. hGCM1 knockdown decreased hCYP19A1 and hCG␤ expression, substantiating its important role in human trophoblast differentiation. Expression of the c-Myc proto-oncogene was increased in proliferating cytotrophoblasts compared to that in differentiated syncytiotrophoblast. Moreover, c-Myc overexpression upregulated miR-17ϳ92 and inhibited hCYP19A1 and hCG␤ expression. Binding of endogenous c-Myc to genomic regions upstream of the miR-17ϳ92 and miR-106aϳ363 clusters in cytotrophoblasts dramatically decreased upon syncytiotrophoblast differentiation. Intriguingly, we observed higher levels of miR-106a and -19b and lower aromatase and hGCM1 expression in placentas from preeclamptic women than in placentas from gestation-matched normotensive women. Our findings reveal that c-Myc-regulated members of the miR-17ϳ92 and miR106aϳ363 clusters inhibit trophoblast differentiation by repressing hGCM1 and hCYP19A1 and suggest that aberrant regulation of these miRNAs may contribute to the pathogenesis of preeclampsia.T he multinucleated syncytiotrophoblast of the human placenta is formed by fusion of underlying proliferating cytotrophoblasts. This multinucleated cell layer, which covers the chorionic villi, is bathed in maternal blood and performs several essential functions to ensure growth and survival of the developing embryo. These include transport of O 2 and nutrients and synthesis and secretion of syncytiotrophoblast-specific protein and steroid hormones, including estrogen and progesterone. Synthesis of estrogens from C 19 steroids is catalyzed by aromatase P450 (P450arom, product of the hCYP19A1 gene). The ability of the human placenta to synthesize estrogens is vastly increased after the ninth week of gestation (1), in association with cytotrophoblast invasion and enlargement of the uterine arterioles, increased blood flow, and O 2 availability to the floating chorionic villi (2, 3). Trophoblast stem cells and cytotrophoblasts do not express hCYP19A1/aromatase; however, when cytotrophoblasts fuse to form multinucleated syncytiotrophoblast, aromatase is markedly induced (4, 5). The exceptionally high levels of placental aromatase likely function to metabolize large amounts of C 19 steroids produced by the human fetal adrenals (e.g., dehydroepiandrosterone), thus preventing conversion of these steroids t...

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“…91,104 The involvement of miRNAs in human trophoblast differentiation was demonstrated recently when the members of the miR-17-92 cluster as well as the miR-106a-363 family, which are regulated by c-myc oncoprotein, were found to inhibit trophoblast differentiation via repression of aromatase (hCYP19A1) and the transcription factor responsible for murine labyrinthine trophoblast development (human GCM1 or hGCM1). 105 Another miRNA, miR-29b, that appears to have a similar role to the miR-17-92 cluster, has also been implicated in pre-eclampsia. 106 miR-29b is involved in apoptosis, angiogenesis, and trophoblast invasion.…”