Examining the context of cytochrome P450 27C1-mediated retinoid desaturation in the skin

Abstract

Regulation of keratinocyte proliferation and differentiation is important to maintain skin function. Retinoic acids, the active form of retinoids, play a role in this regulation by inducing or repressing the expression of hundreds of genes. In keratinocytes, there exists two parallel pathways of retinoids: the all-trans retinoids and the 3,4-dehydroretinoids. 3,4-Dehydroretinoids make up about ~25% of the epidermal retinoid pool but their function and formation are poorly understood in comparison with their all-trans retinoid counterparts. 3,4-Dehydroretinoids are formed from all-trans retinoids, but the enzyme responsible for this was previously unidentified. Cytochrome P450 27C1 is expressed in the skin and has also been shown to desaturate retinoids in vitro. Because of this, the overarching hypothesis for this project is that P450 27C1 is the previously unidentified retinoid desaturase in the skin. To test this hypothesis, and to further characterize P450 27C1, this work is focused on four project areas. First is assessing the localization of P450 27C1 within the skin and quantifying it along with the P450 redox partners. The second is characterizing the interaction between P450 27C1 and adrenodoxin, its redox partner protein. Third, is determining if and how P450 27C1 interacts with cellular retinoid binding proteins. Lastly, is assessing potential functions for P450 27C1 and 3,4-dehydroretinoids. This work utilizes a combination of biochemical, analytical, and molecular biology techniques to address these areas. In summary, P450 27C1 was found to be localized to keratinocytes of the epidermis and was able to interact with cellular retinoid binding proteins, supporting its assignment as the in vivo retinoid desaturase. P450 27C1 was found to bind to adrenodoxin tightly in multiple conformations, but adrenodoxin did not appear to be an allosteric effector of P450 27C1 retinoid binding. Additionally, 3,4-dehydroretinoids were found to be resistant to the catabolic processes that all-trans retinoids undergo, suggesting that they may be a more stable form of retinoids within the cell. Overall, this work adds to the knowledge-base of physiological retinoid homeostasis and cytochrome P450 enzymology.