3-Methylcholanthrene, Which Binds to the Arylhydrocarbon Receptor, Inhibits Proliferation and Differentiation of Osteoblasts in Vitro and Ossification in Vivo

Abstract

3-Methylcholanthrene (3MC) is a ligand for arylhydrocarbon receptor (AhR), which binds dioxin. We examined the effects of 3MC on the proliferation and differentiation of osteoblasts using cultures of rat calvarial osteoblast-like cells (ROB cells) and mouse calvarial clonal preosteoblastic cells (MC3T3-E1 cells). Analysis by RT-PCR revealed that the mRNAs for AhR and AhR nuclear translocators were expressed in both ROB and MC3T3-E1 cells. Cell proliferation and the synthesis of DNA by ROB cells and MC3T3-E1 cells were markedly inhibited on exposure of cells to 3MC. Furthermore, 3MC reduced the activity of alkaline phosphatase and the rate of deposition of calcium by cells. The level of expression of mRNA for osteocalcin, which is a marker of osteoblastic differentiation, was also depressed by 3MC. Moreover, when 3MC (1 mg/kg body weight) was administered sc to pregnant mice at 10.5, 12.5, and 14.5 d post coitus, fetuses examined subsequently at 15.5 or 17.5 d post coitus revealed evidence of inhibition of appropriate calcification of bones. The treated metacarpals showed no subperiosteal bone matrix histologically. Our findings indicate that 3MC might have critical effects on the formation of bone both in vivo and in vitro.

Pure estrogenic effect of benzophenone-2 (BP2) but not of bisphenol A (BPA) and dibutylphtalate (DBP) in uterus, vagina and bone

“…Hence, despite binding of BPA to ER␣ and ER␤ with low affinity, this suggests that other mechanisms not mediated via ER␣ or ER␤ may be involved in regulating bone metabolism. It is known that the bone amply expresses the aryl hydrocarbon receptor (AhR = dioxin receptor) (Singh et al, 2000;Jamsa et al, 2001;Naruse et al, 2002) and that agonists of the receptor decrease osteoblast activity in vitro (Naruse et al, 2002). The AhR is a ligandactivated transcription factor, which upon dimerization with the AhR nuclear translocator (AhRNT), functions as a repressor of ER␣ effects (Safe et al, 2000;Jacobs et al, 2003).…”

The Nuclear Receptor AhR Controls Bone Homeostasis by Regulating Osteoclast Differentiation via the RANK/c-Fos Signaling Axis

“…AhR is a ligand-activated transcription factor that can be activated by benzo [a]pyrene (BaP) and polycyclic aromatic hydrocarbons such as 3-methylcholanthrene and 29,39,79,89-tetrachlorodibenzo-p-dioxin (2,3). Under physiological conditions, AhR localizes to the cytoplasm in a complex with other proteins such as heat shock protein (HSP)90, XAP2, and p23 (4).…”

The Effects of Smoke Carcinogens on Bone

“…The addition of the PAH or 3MC to osteoblasts can inhibit the formation and differentiation of cultured osteoblasts [22]. In addition, 3MC-treated mice showed delayed ossification of forelimb, hindlimb, and cervical and thoracic vertebrae in fetal mice.…”