Functional characterization of a natural retinoic acid responsive element

Area of Science:

• Molecular Endocrinology
• Gene Regulation

Background:

• Retinoic acid receptor (RAR) and thyroid hormone receptor (T3R) typically bind response elements as dimers to inverted repeats.
• A distinct retinoic acid response element (beta RARE) in the RAR beta 2 gene promoter features direct repeats.

Purpose of the Study:

• To investigate the binding and transactivation capabilities of RARs on the beta RARE.
• To compare the DNA response element preferences of RAR and T3R.

Main Methods:

• Demonstration of RAR alpha, beta, and gamma binding and transactivation through the beta RARE.
• Analysis of motif arrangement (direct repeats vs. palindrome) and spacing effects on receptor activity.
• Testing transactivation by RAR and T3R on various response elements, including the Moloney murine leukaemia virus T3RE.

Main Results:

• RARs effectively bind and transactivate through the direct repeats of the beta RARE.
• Palindrome arrangement of beta RARE motifs did not confer retinoic acid responsiveness.
• T3R showed a preference for direct repeats spaced by five nucleotides over six.
• RAR exhibited greater flexibility in spacing requirements for direct repeats.
• A single nucleotide change in the MoMLV T3RE created a promiscuous RA/T3 responsive element.

Conclusions:

• The beta RARE comprises two direct repeats, mediating retinoic acid response.
• RAR and T3R exhibit distinct preferences for DNA response element structure and spacing.
• Modifying specific response elements can lead to dual receptor activation, suggesting potential for cross-talk.