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Reactive oxygen species (ROS) are by-products of metabolism of oxygen and they play an important role in normal homeostasis and cell signaling, as well as in the initiation of diseases including cancer when their production is upregulated. Thus, it is imperative to understand the cellular and molecular basis by which ROS impact on various biological and pathological processes. In this report, we show that human keratinocyte cell line (HaCaT) treated with hydrogen peroxide displayed an increased activity of AhR, leading to enhanced expression of its downstream targets including cytochrome P450 genes. Intriguingly, preincubation of the complete culture medium with hydrogen peroxide accelerated AhR activation and its downstream signaling. Subsequent mass spectrometric analysis reveals that the oxidant elicits the production of oxindole, a tryptophan catabolic product. We further demonstrate that 2-oxindole (a major form of oxindole) is capable of activating AhR, strongly suggesting that ROS may exert a significant impact on AhR signaling. Consistent with this, we also observe that hexavalent chromium [Cr(VI)], a heavy metal known to generate ROS in vivo, enhances AhR protein levels, as well as stimulates expression of CYP1A2 in an AhR-dependent manner. Significantly, we show that hydrogen peroxide and 2-oxindole induce expression of IDO1 and PD-L1, two immune checkpoint proteins. Given the role of IDO1 and PD-L1 in mediating T cell activity and/or differentiation, we postulate that ROS in the tumor microenvironment may play a crucial role in immune suppression via perturbing AhR signaling.

Objectives Besides its role in regulating phosphatidylinositol‐3 kinase (PI3K) signalling in the cytosol, PTEN also has a nuclear function. In this study, we attempted to understand the mechanism of chromatin PTEN in suppressing chromosomal instability during cell division. Materials and methods Immunocoprecipitation, ectopic expression, and deletional analyses were used to identify the physical interaction between Chromobox Homolog protein 8 (CBX8) and PTEN, as well as the functional domain(s) of PTEN mediating the interaction. Cell synchronization followed by immunoblotting was employed to study cell cycle regulation of CBX8 and the functional interaction between chromatin PTEN and CBX8. Small interfering RNAs (siRNAs) were used to study the role of PTEN and CBX8 in modulating histone epigenetic markers during the cell cycle. Results Polycomb group (PcG) proteins including CBXs function to repress gene expression in a wide range of organisms including mammals. We recently showed that PTEN interacted with CBX8, a component of Polycomb Repressing Complex 1 (PRC1), and that CBX8 co‐localized with PTEN in the nucleus. CBX8 levels were high, coinciding with its phosphorylation in mitosis. Phosphorylation of CBX8 was associated with monoubiquitinated PTEN and phosphorylated‐BubR1 on chromatin. Moreover, CBX8 played an important role in cell proliferation and mitotic progression. Significantly, downregulation of either PTEN or CBX8 induced H3K27Me3 epigenetic marker in mitotic cells. Conclusion CBX8 is a new component that physically interacts with chromatin PTEN, playing an important role in regulating mitotic progression., Nuclear PTEN plays a role in regulating mitotic progression. CBX8 is phosphorylated during mitosis. CBX8 physically interacts with PTEN, as well as mitotic checkpoint components (MCC). The molecular complex functions to block trimethylation of lysine27 of histone H3 (H3K27Me3), which appears to be an essential molecular process for mediating mitotic exit and G1 entry.

The tumor suppressor PTEN plays an important role in the regulation of cell survival, proliferation, and angiogenesis. Deregulated expression and/or activities of PTEN frequently result in tumor development. PTEN is a plasma-membrane lipid-phosphatase, functioning to antagonize the PI3K/AKT signaling pathway. It also has a role in the nucleus regulating mitotic progression and suppressing chromosomal instability during cell division. To date, the exact function of nuclear PTEN remains not entirely clear. Several recent studies have revealed that PTEN physically interacts with histones and regulates their post-translational modifications. We previously found that PTEN is heavily phosphorylated by Plk1, which regulates mototic progression and chromosomal instability through its physical interaction with mitotic checkpoint complex (MCC). Therefore, we asked whether PTEN directly interacted with epigenetic regulators and mediated histone modifications and whether PTEN-mediated histone modifications functioned as an important regulatory mechanism during the cell cycle. Here we demonstrated that PTEN was associated with Chromobox Homolog proteins (CBXs) which are part of PRC1 complex that mediates histone modifications. Among CBXs, CBX8 levels were high in mitosis, which were correlated with an increase in PTEN mono-ubiquitination, suggesting its potential involvement in mitotic progression. Supporting this notion, we showed that CBX8 was required for cell proliferation and mitotic progression. Moreover, CBX8 was associated with PTEN/MCC during mitosis and mediated histone H2AK119 mono-ubiquitination. Combined, these results strongly suggest that CBX8/PTEN/MCC plays a significant role in modifying histones and suppressing chromosomal instability during mitotic progression. Citation Format: Byeong Hyeok Choi, Tania Marlyn Colon, Eunji Lee, Ziyue Kou, Wei Dai. PTEN plays a role in histone modifications during mitosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1969.

Aryl hydrocarbon receptor (AHR) was initially discovered as a cellular protein involved in mediating the detoxification of xenobiotic compounds. Extensive research in the past two decades has identified several families of physiological ligands and uncovered important functions of AHR in normal development and homeostasis. Deficiency in AHR expression disrupts major signaling systems and transcriptional programs, which appear to be responsible for the development of numerous developmental abnormalities including cardiac hypertrophy and epidermal hyperplasia. This mini review primarily summarizes recent advances in our understanding of AHR functions in normal physiology with an emphasis on the cardiovascular, gastrointestinal, integumentary, nervous, and immunomodulatory systems.

RAS proteins regulate a variety of cellular processes including cell survival, proliferation, and differentiation. RAS genes are among the most frequently mutated oncogenes in human malignancies. To date, there are no successful anti-cancer drugs in the clinic that target RAS proteins or their pathways. Therefore, it is imperative to identify and characterize new components that regulate RAS activity or mediates its downstream signaling. Recently, we identified a series of proteins that are associated with HRAS using a combination of immunoprecipitation and mass spectrometry. We first focused on RADIL, a gene product with Ras-Association (RA) and DIL domains. RADIL is known to be a downstream effector of RAP1, inhibiting RhoA signaling in the regulation of cell survival, adhesion, and migration. We demonstrated that RADIL interacted with all three isoforms of RAS, including H, N, and KRAS. Interestingly, constitutively active HRAS (HRASG12V) was strongly associated with RADIL whereas dominant negative HRAS (HRASS17N) displayed a compromised association with RADIL, suggesting that RADIL may be required for RAS activation. We also found that Radil Knockout cells had weakened ERK phosphorylation whereas induced expression of RADIL promoted ERK phosphorylation, suggesting that RADIL is required for the RAS-MEK-ERK signaling cascade in vitro. Taken together, our current studies strongly suggest that RADIL may be important for regulating RAS signaling. Citation Format: Byeong Hyeok Choi, Ziyue Kou, Mark R. Philips, Wei Dai. RADIL regulates RAS downstream signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1791.