Activin regulates luteinizing hormone beta-subunit gene expression through Smad-binding and homeobox elements

Area of Science:

• Endocrinology
• Molecular Biology
• Genetics

Background:

• Luteinizing hormone beta-subunit (LHbeta) is crucial for ovulation and reproductive success.
• LHbeta is synthesized in pituitary gonadotropes, and its regulation is key to reproductive function.

Purpose of the Study:

• To investigate the molecular mechanisms by which activin induces LHbeta gene expression.
• To identify the specific DNA elements and transcription factors involved in activin-mediated LHbeta regulation.

Main Methods:

• Primary mouse pituitary cell cultures and immortalized LbetaT2 gonadotrope cells were used.
• Analysis of LHbeta and FSHbeta mRNA levels in wild-type and Smad3-deficient mice.
• Reporter gene assays to identify regulatory elements in the LHbeta gene promoter.
• Electrophoretic mobility shift assays (EMSAs) and co-immunoprecipitation to study protein-DNA and protein-protein interactions.

Main Results:

• Activin treatment induced LHbeta gene expression in primary pituitary cells within 24 hours.
• Male mice deficient in Smad3 exhibited reduced LHbeta and FSHbeta mRNA expression.
• A promoter-proximal region (-121/-86) of the rat LHbeta gene was identified as essential for activin responsiveness.
• Maximal induction required a homeobox element (HB), an Egr site, and three Smad-binding elements (SBEs).
• Smad proteins were necessary and sufficient for activin induction and could bind to an SBE.
• Smad proteins interacted with Ptx-1 and Otx-1, which bind to the HB.

Conclusions:

• Activin induction of LHbeta gene expression is mediated by Smad proteins binding to specific SBEs in the promoter.
• The process involves cooperation between Smad proteins, homeobox transcription factors (Ptx-1, Otx-1), and other regulatory elements.
• This intricate regulatory network ensures proper LHbeta gene expression for reproductive function.