Retinoids enhancement factor

We have begun to characterize the retinoid enhancement factor. Reconstitution studies clearly show that the factor is present in the post-microsomal soluble fraction (Table III) in rat liver (there is a factor(s) present in the 17,000xg pellet which normally inhibits this factor (Table III)). The retinoid enhancing factor is heat sensitive, since its activity in the presence of retinol is lost when supernatant is incubated for 15 minutes at 45°C (Figure 3). Similar results were obtained by incubating the supernatant at 50°C for five minutes. 

Retinoids. The term retinoid refers to retinol or other closely related derivatives, either natural or synthetic. Retinoids may or may not have retinol-like (vitamin A-like) activity. Retinoids affect epithelial cells by binding to receptors inside these cells, inducing alterations in the transcription of genes. Retinoids enhance the synthesis of some proteins, such as proteins that serve as receptors for certain hormones and growth factors, and reduce the synthesis of others. Some of the most commonly prescribed treatments for acne—tretinoin, isotretinoin, and adapalene—are retinoids. (See Table 1.)... 

In normal cells, the erqjression of RARs is enhanced by retinoids. Many cancer cells lose the ability to respond to retinoids because they lack COUP-TF (a mammalian ecdysone-like transcription factor). Expression of COUP-TF in cancer cells can restore the retinoid response. Apparently, COUP-TF is required for the interaction of the RARs with the transcriptional co-activator CBP, enhancing DNA binding. ... 

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