PDZ Scaffold Protein CAL Couples with Metabotropic Glutamate Receptor 5 to Protect Against Cell Apoptosis and Is a Potential Target in the Treatment of Parkinson's Disease.

Targeting mGluR5 has been an attractive strategy to modulate glutamate excitotoxicity for neuroprotection. Although human clinical trials using mGluR5 negative allosteric modulators (NAMs) have included some disappointments, recent investigations have added several more attractive small molecules to this field, providing a promise that the identification of more additional strategies to modulate mGluR5 activity might be potentially beneficial for the advancement of PD treatment. Here, we determined the role of the interacting partner CAL (cystic fibrosis transmembrane conductance regulator-associated ligand) in mGluR5-mediated protection in vitro and in vivo. In astroglial C6 cells, CAL deficiency blocked (S)-3, 5-dihydroxyphenylglycine (DHPG)-elicited p-AKT and p-ERK1/2, subsequently prevented group I mGluRs-mediated anti-apoptotic protection, which was blocked by receptor antagonist 1-aminoindan-1, 5-dicarboxylic acid (AIDA), and PI3K or MEK inhibitor LY294002 or U0126. In rotenone-treated MN9D cells, both CAL and mGluR5 expressions were decreased in a time- and dose-dependent manner, and the correlation between these 2 proteins was confirmed by lentivirus-delivered CAL overexpression and knockdown. Moreover, CAL coupled with mGluR5 upregulated mGluR5 protein expression by inhibition of ubiquitin-proteasome-dependent degradation to suppress mGluR5-mediated p-JNK and to protect against cell apoptosis. Additionally, CAL also inhibited rotenone-induced glutamate release to modulate mGluR5 activity. Furthermore, in the rotenone-induced rat model of PD, AAV-delivered CAL overexpression attenuated behavioral deficits and dopaminergic neuronal death, while CAL deficiency aggravated rotenone toxicity. On the other hand, the protective effect of the mGluR5 antagonist MPEP was weakened by knocking down CAL. In vivo experiments also confirmed that CAL inhibited ubiquitination-proteasome-dependent degradation to modulate mGluR5 expression and JNK phosphorylation. Our findings show that CAL protects against cell apoptosis via modulating mGluR5 activity, and may be a new molecular target for an effective therapeutic strategy for PD.

Adiponectin induces apoptosis in hepatocellular carcinoma through differential modulation of thioredoxin proteins.

Adiponectin blocks hepatocellular carcinoma (HCC) progression by inducing cell apoptosis through the modulation of C-Jun N-terminal kinase and mammalian target of rapamycin. However, the precise upstream signaling pathways or molecules remain elusive. In the present study, we analyzed the role of antioxidant protein thioredoxin (Trx) in adiponectin-induced apoptosis in HCC. Adiponectin treatment decreased the viabilities of both HepG2 and Huh7 HCC cells accompanied by increased accumulation of intracellular reactive oxygen species, as evidenced by 2',7'-dichlorodihydrofluorescein diacetate staining. Pretreatment of these cells with the deoxidant N-acetylcysteine blocked the inhibitory effect of adiponectin. Levels of Trx2 protein in both HCC cells were significantly decreased, and the level of Trx1 was significantly inhibited in Huh7 cells while unchanged in HepG2 cells. However, the redox state of Trx1 was altered from reduced to the oxidized form following adiponectin treatment in HepG2 cells. Overexpression of both Trx proteins rescued adiponectin-induced cell apoptosis, whereas mutated Trx proteins were less effective. Further analysis suggested that both ASK1 and JNK signaling are involved in this process. Trx1 and Trx2 proteins also manifested protective effects on HCC cells in response to adiponectin treatment in a xenograft tumor model. Furthermore, high levels of Trx proteins and low adiponectin expression levels were found in primary human HCC samples compared with paracancerous tissues. These results suggest that Trx proteins play important roles in mediating adiponectin-induced HCC cell apoptosis, thus providing new insights into the pathogenesis of HCC and identifying adiponectin and Trx proteins as potential combinational therapeutic targets for the treatment of HCC.