Relationships among the cell cycle, cell proliferation, and aryl hydrocarbon receptor expression in PLHC-1 cells

Aryl hydrocarbon receptor (AHR) ligands such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) cause altered cell proliferation in many tissues in vivo and cell types in vitro, and the AHR has been suggested to play a role in cell cycle regulation in mammalian systems. However, the mechanisms underlying these effects are poorly understood. The overall objective of the present work was to investigate possible interactions between cell proliferation, the cell cycle, and AHR signal transduction in a piscine system, the PLHC-1 cell line, which is being used increasingly in aquatic toxicological research. The specific objectives were to characterize proliferation rates and the cell cycle in these cells, to measure effects of TCDD on cell proliferation, and to determine if expression of the AHR varies during the cell cycle. The doubling time of PLHC-1 cells was determined to be 22 h, and the durations of the G1, S and G2/M stages of the cell cycle were 13, 3, and 6 h, respectively. A minimum seeding density of 1.2 x 10(5) cells/cm(2) in medium with 10% calf serum and 0.3 x 10(5) cells/cm(2) in 10% fetal bovine serum was found to be required for subsequent proliferation. Of several cell cycle inhibitors tested, only aphidicolin and nocodazole were effective for obtaining synchronous cell populations. TCDD was found to inhibit PLHC-1 cell proliferation in a time- and dose-dependent manner in multiple passages of one sub-clone, but not in several other sub-clones. Neither AHR mRNA nor protein expression varied during the cell cycle, as measured by RT-PCR and specific binding of [(3)H]TCDD in synchronous PLHC-1 cells. This work establishes techniques for identifying and characterizing possible interactions between the cell cycle and AHR signal transduction in PLHC-1 cells. Taken together, the results indicate that PLHC-1 cells are amenable to analysis of AHR-cell cycle interactions, but that heterogeneity of sub-clones may complicate their use for investigating AHR-mediated changes in proliferation.