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Prolactin inhibits auto- and cross-induction of thyroid hormone and estrogen receptor and vitellogenin genes in adult Xenopus (Amphibia) hepatocytes
Elida Μ.L. RabelοI; Jamshed R. ΤαtaII
IDepartamento de Parasitologia, ICB, UFMG, Av. Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brasil. Send correspondence to E.M.L.R.
IILaboratory of Developmental Biochemistry, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW71ΑΑ, UK.
ABSTRACT
It is well known that virtually every tissue f the amphibian larvae is highly sensitive to the mutually antagonistic actions f thyroid hormone (TH) and prolactin (PRL), but it is not known if adult amphibian tissues respond similarly to these two hormones. We have previously shown that very low doses of triiodothyronine (T3) rapidly and strongly potentiate the activation f silent vitellogenin (Vit) genes by estrogen (E2) and the autoinduction of estrogen receptor (ER) transcripts in primary cultures f adult Xenopus hepatocytes. This response to T3 is accompanied by the upregulation f thyroid hormone receptor β (ΤRβ) mRNA. Using Northern blot and RNase protection assays, we now show that ovine PRL added for 12 h along with 2 x 10-9 M Τ3 will completely prevent potentiation f Ε2 induction of Vit mRNA in primary cultures f adult Xenopuus hepatocytes. PRL also abolished the auto-upregulation f ΤRβ mRNA and the cross-activation f autoinduction of ER mRNA. Thus, we show for the first time that the anti-TH action f PRL that is manifested in Xenopuus tadpole tissues during metamorphosis is retained in adult liver, and suggest that the mutually antagonistic actions f the two hormones may be brought about by similar molecular mechanisms in larval and adult amphibian tissues.
Keywords: Prolactin; thyroid hormone; estrogen; Xenopus; Amphibia.
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