The AHR Pathway And Its Potential Role In The Regulation Of The 15 kDa Selenoprotein

Abstract

Several selenoproteins, including the 15kDa selenoprotein (Sep15), are thought to have roles in both cancer prevention and promotion. Sep15 belongs to the group of stress‐related selenoproteins, and though its functional role continues to be elucidated, this oxidoreductase resides in the ER and is thought to be involved in reduction or isomerization of disulfide bonds. Little is known about factors regulating Sep15 expression. Our preliminary analyses indicated that some dietary polyphenols decreased Sep15 mRNA expression in human colon cancer HT29 cells. Because many of these flavonoids are known to affect Arylhydrocarbon Receptor (AHR) and/or NRF2‐regulatory pathways, expression of AHR and NRF2‐related genes are being investigated in Sep15‐deficient and ‐sufficient HT29 colon cancer cells to elucidate the potential regulatory mechanisms of Sep15. Analysis of previously published microarray data indicated that mRNA expression of AHR‐pathway‐related genes was significantly changed in HT29 cells lacking Sep15 compared to controls, including the AHR‐nuclear transporter, the AHR‐interacting protein, and heat‐shock protein 90. Comparison of the NCI‐60 cell lines through CellMiner analysis revealed that mRNA expression of Sep15 and AhR was negatively correlated (p<0.05). Furthermore, treatment of HT29 cells with the NRF2‐agonist, sulforaphane, did not increase Sep15 mRNA expression. Thus, in the current study, HT 29 control and shSep15 cells were exposed to 2,3,7,8‐Tetrachlorodibenzo‐p‐dioxin (TCDD) or 5,6‐beta‐naphthoflavone to induce or inhibit the AHR‐signaling pathway. Gene expression is currently being assessed using qPCR and Western blotting. Preliminary analyses show that mRNA expression of TCCD‐induced CYP1A1 and CYP1B1 is significantly lower in Sep15‐deficient cells compared to controls. Independent of TCDD treatment, shSep15 cells also expressed a lower CYP1A2 mRNA expression than the control cells. Nuclear and cytosolic protein expression is currently being assessed. Preliminary results suggest that Sep15 may influence or be regulated by AhR‐dependent pathways, which may be important in regulation of colon carcinogenesis.Support or Funding InformationNational Cancer Institute Intramural support; Towson University Jess & Mildred Fisher Endowed Chair and a Faculty Development & Research Committee grant (PAT).