Metabolic bioactivation of polycyclic aromatic hydrocarbons, such as the environmental procarcinogen benzo [a]pyrene, is catalyzed by a cytochrome P450 monooxygenase encoded by the substrate-inducible Cyp1a1 gene. Cyp1a1 induction requires trans-activation by the heterodimeric transcriptional complex formed by the liganded Ah receptor (AHR) and its partner, ARNT. Previously, we showed that constitutively bound HDAC1 dissociates from Cyp1a1 promoter chromatin after ligand-mediated induction, concomitantly with the recruitment of AHR/ARNT complexes and p300. Here, we investigated the hypothesis that HDAC1 binding maintains the Cyp1a1 gene in a silenced state in uninduced cells. We find that Cyp1a1 induction by the AHR/ ARNT is associated with modification of specific chromatin marks, including hyperacetylation of histone H3K14 and H4K16, trimethylation of histone H3K4, and phosphorylation of H3S10. HDAC1 and DNMT1 form complexes on the Cyp1a1 promoter of uninduced cells but HDAC1 inhibition alone is not sufficient to induce Cyp1a1 expression, although it allows for the hyperacetylation of H3K14 and H4K16 to levels similar to those found in B[a]P-induced cells. These results show that by blocking modification of histone marks, HDAC1 plays a central role in Cyp1a1 expression and that its removal is a necessary but not sufficient condition for Cyp1a1 induction, underscoring the requirement for a concerted series of chromatin remodeling events to complete the initial steps of gene trans-activation by the Ah receptor.

Cellular stress by DNA damage induces checkpoint kinase-2 (CHK2)-mediated phosphorylation and stabilization of the E2F1 transcription factor, leading to induction of apoptosis by activation of a subset of proapoptotic E2F1 target genes, including Apaf1 and p73. This report characterizes an interaction between the aryl hydrocarbon (Ah) receptor (AHR), a ligand-activated transcription factor, and E2F1 that results in the attenuation of E2F1-mediated apoptosis. In Ahr ؊/؊ fibroblasts stably transfected with a doxycycline-regulated AHR expression vector, inhibition of AHR expression causes a significant elevation of oxidative stress, ␥H2A.X histone phosphorylation, and E2F1-dependent apoptosis, which can be blocked by small interfering RNA-mediated knockdown of E2F1 expression. In contrast, ligand-dependent AHR activation protects these cells from etoposide-induced cell death. In cells expressing both proteins, AHR and E2F1 interact independently of the retinoblastoma protein (RB), because AHR and E2F1 coimmunoprecipitate from extracts of RBnegative cells. Additionally, chromatin immunoprecipitation assays indicate that AHR and E2F1 bind to the Apaf1 promoter at a region containing a consensus E2F1 binding site but no AHR binding sites. AHR activation represses Apaf1 and TAp73 mRNA induction by a constitutively active CHK2 expression vector. Furthermore, AHR overexpression blocks the transcriptional induction of Apaf1 and p73 and the accumulation of sub-G 0 /G 1 cells resulting from ectopic overexpression of E2F1. These results point to a proproliferative, antiapoptotic function of the Ah receptor that likely plays a role in tumor progression. INTRODUCTIONMembers of the E2F family of transcription factors are critical regulators of the G 1 /S phase transition of the cell cycle, during which their transcriptional activity is generally controlled through interaction with retinoblastoma (RB) family proteins. In addition, E2F proteins have functions beyond the G 1 /S phase transition that impact cell proliferation in a variety of ways (Dimova and Dyson, 2005). The E2F family consists of six extensively characterized and three less wellstudied members. E2F1, -2, and -3a are potent activators of transcription, bind exclusively to RB-p105, and are cyclically expressed during the cell cycle. E2F3b and -4, which can interact with RB-p107 and -p130, and E2F5, which binds only to p130, are poor transcriptional activators, and they function mainly as repressors through their recruitment of RB proteins to E2F-regulated promoters (Dyson, 1998;Nevins, 1998;DeGregori and Johnson, 2006). In general, the E2Fs with transactivator activity promote cell cycle progression, whereas the E2Fs with transrepressor activity function in cell cycle exit and differentiation (Dimova and Dyson, 2005). E2F6-8 are distinct from the other E2F members, lacking the transactivation and RB-binding domains, and they repress transcription in an RB-independent manner (Frolov and Dyson, 2004;DeGregori and Johnson, 2006).The best-characterized function of E2F ...

Objectives: To investigate the role of lingual lymph node (LLN) metastasis on locoregional control (LRC) in patients with locally advanced tongue squamous cell carcinoma (SCC).Methods: A total of 231 patients were prospectively enrolled. Analyses focused on the association between the LLN metastasis and clinical pathologic variables as well as the significance of LLN metastasis in predicting prognosis.Results: LLNs were noted in 58 patients, 33 of whom were positive for LLN metastasis. LLN metastasis was significantly related to adverse pathologic characteristics. In patients with LLN metastasis, the 5-year LRC rate was 45%. In patients without LLN metastasis, the 5-year LRC rate was 65% and the difference was significant (P = 0.013). Further, Cox model analysis confirmed the independence of LLN metastasis from prognosis prediction.Conclusion: LLN metastasis in locally advanced tongue SCC is relatively uncommon; however, LLNs should be routinely dissected because they could significantly decrease locoregional control.