Involvement of retinoic acid retinoid receptors in the regulation of murine αB-crystallin small heat shock protein gene expression in the lens

Crystallins are a diverse group of abundant soluble proteins that are responsible for the refractive properties of the transparent eye lens. me showed previously that Pax-6 can activate the alpha B-crystallin/small heat shock protein promoter via the lens specific regulatory regions LSR1 (-147/-118) and LSR2 (-78/-46). Here we demonstrate that retinoic acid can induce the accumulation of alpha B-crystallin in N/N1003A lens cells and that retinoic acid receptor heterodimers (retinoic acid receptor/retinoid X receptor; RAR/RXR) can transactivate LSR1 and LSR2 in cotransfection experiments. DNase I footprinting experiments demonstrated that purified RAR/RXR heterodimers will OCCUPY sequences resembling retinoic acid response elements within LSR1 and LSR2. Electrophoretic mobility shift assays using antibodies indicated that LSR1 and LSR2 can interact with endogenous RAR/RXR complexes in extracts of cultured lens cells. Pax-6 and RAR/RXR together had an additive effect on the activation of alpha B-promoter in the transfected lens cells. Thus, the alpha B-crystallin gene is activated by Pax-6 and retinoic acid receptors, making these transcription factors examples of proteins that have critical roles in early development as well as in the expression of proteins characterizing terminal differentiation.