We employed the suppressive subtractive hybridization to identify 41 up- and downregulated transcripts in Jurkat cells after benzo[a]pyrene (BaP) treatment. Among the 21 downregulated transcripts, we found that BaP suppresses the Keap1 transcript by 7.5-fold. Subsequent analyses revealed that BaP significantly suppresses the Keap1 message and protein levels to about 40 and 60%, respectively, of the vehicle controls in Jurkat cells without reactive oxygen species involvement. In addition, the nuclear Nrf2 (nuclear factor erythroid 2-related factor) protein content is significantly increased by 2.6-fold. The same BaP treatment to Hepa1c1c7 cells also downregulates the Keap1 message and protein levels to a similar extent. When we treated Jurkat cells with 3-(4-morpholinyl)propyl isothiocyanate, which is known to increase the amount of the Nrf2 content, we found that there is no change in the Keap1 message, but the amount of the Keap1 (kelch-like ECH-associated protein 1) protein is reduced to 75% of the vehicle controls. Although both Nrf2 target messages nqo1 and gstp1 are upregulated by BaP in Jurkat cells, only GSTP1 is upregulated at the protein level. Unlike Hepa1c1c7 cells, Jurkat cells have no detectable aryl hydrocarbon receptor and BaP metabolites, minimal CYP1A1 activity, and no quinone oxidoreductase 1 (NQO1) activity. We concluded that BaP, but not its metabolites, increases the amount of the nuclear Nrf2 protein by downregulating the Keap1 message in Jurkat cells.

Background: Aryl hydrocarbon receptor (AHR), commonly known as an environmental sensor involved in the metabolism and elimination of xenobiotic substances, is also an important modulator in the development and functioning of the immune system. AHR expression is varied in the T cell subsets with the highest expression in T-helper 17 and T regulatory cells. It has been reported that AHR can act as a tumor promoter or a tumor suppressor, depending on the tumor type. Methods: In an effort to understand the role played by AHR in tumor growth, the MC38 syngeneic colon carcinoma tumor model was used on C57BL/6 or ahr knockout (KO, -/-) mice with or without AHR antagonist (CH223191) treatment. Tumor sizes were measured, and biomarkers were quantified in tumor microenvironment and draining lymph nodes using flow cytometry. Enzyme-linked immunosorbent assay was used to determine the amount of cytokines in tumors. Results: In ahr deficient mice, MC38 tumors progress more rapidly than in wild-type mice, accompanied by an increase in tumor-associated macrophages and M2 macrophages and a decrease in CD8a positive cytotoxic lymphocytes. Analysis of cytokines in the tumor microenvironment reveals a pro-inflammatory phenotype. Similar changes were observed by pharmacologic blockade of the receptor using CH223191. Conclusion: AHR acts as a tumor suppressor in mice implanted with MC38 colon carcinoma cells as evidenced by either a blockade or deficiency of AHR.

The aryl hydrocarbon receptor (AHR) is an environmental sensing molecule which impacts diverse cellular functions such as immune responses, cell growth, respiratory function, and hematopoietic stem cell differentiation. It is widely accepted that the degradation of AHR by 26S proteasome occurs after ligand activation. Recently, we discovered that HeLa cells can modulate the AHR levels via protein degradation without exogenous treatment of a ligand, and this degradation is particularly apparent when the p23 content is down-regulated. Inhibition of autophagy by a chemical agent (such as chloroquine, bafilomycin A1, or 3-methyladenine) increases the AHR protein levels in HeLa cells whereas activation of autophagy by short-term nutrition deprivation reduces its levels. Treatment of chloroquine retards the degradation of AHR and triggers physical interaction between AHR and LC3B. Knockdown of LC3B suppresses the chloroquine-mediated increase of AHR. Down-regulation of p23 promotes AHR degradation via autophagy with no change of the autophagy-related gene expression. Although most data in this study were derived from HeLa cells, human lung (A549), liver (Hep3B), and breast (T-47D and MDA-MB-468) cells also exhibit AHR levels sensitive to chloroquine treatment and AHR–p62/LC3 interactions. Here we provide evidence supporting that AHR undergoes the p62/LC3-mediated selective autophagy in HeLa cells.