H2O2-induces upregulation of Fas and Fas ligand expression in NGF-differentiated PC12 cells: modulation by cAMP

Fas, (APO-1/CD95), a transmembrane glycoprotein belonging to the tumor necrosis (TNF) receptor superfamily, transduces apoptotic death upon crosslinking by its cognate ligand (FasL). As upregulation of Fas/FasL expression occurs in neuropathological conditions (e.g., stroke, central nervous system [CNS] trauma and seizures) associated with oxidative damage, we questioned whether reactive oxygen species (ROS) can directly affect Fas and FasL expression in neuronal cells. Utilizing rat PC12 cells neuronally differentiated with nerve growth factor (NGF), we observed that concentrations of H₂O₂ inducing apoptotic cell death rapidly trigger the expression of Fas mRNA and protein as well as FasL mRNA. Although NGF-addition to naive PC12 downregulated constitutive Fas and FasL transcription, the H₂O₂-induced Fas and FasL mRNA upregulation invariably occurred either in the presence or in the absence of NGF. Similarly, phorbol 1,2-myristate 1,3-acetate (PMA), a potent protein kinase C (PKC) activator, did not modify Fas and FasL mRNA upregulation subsequent to H₂O₂ exposure. On the contrary, forskolin and dibutyryl cAMP, which elevate intracellular cAMP by independent mechanisms, both counteracted H₂O₂-induced Fas, but not FasL, mRNA upregulation and increased constitutive expression of FasL mRNA. Altogether, our data show that oxidative stress is a major stimulus in eliciting Fas and FasL expression in NGF-differentiated PC12 cells. Moreover, we describe here for the first time the existence of cAMP-dependent mechanism(s) modulating Fas and FasL expression.