Prion diseases are fatal neurodegenerative diseases resulting from misfolding of normal cellular prion (PrP C ) into an abnormal form of scrapie prion (PrP Sc ). The cellular mechanisms underlying the misfolding of PrP C are not well understood. Since cellular prion proteins harbor divalent metal-binding sites in the N-terminal region, we examined the effect of manganese on PrP C processing in in vitro models of prion disease. Exposure to manganese significantly increased PrP C levels both in cytosolic and in membrane-rich fractions in a time-dependent manner. Manganese-induced PrP C upregulation was independent of messenger RNA transcription or stability. Additionally, manganese treatment did not alter the PrP C degradation by either proteasomal or lysosomal pathways. Interestingly, pulse-chase analysis showed that the PrP C turnover rate was significantly altered with manganese treatment, indicating increased stability of PrP C with the metal exposure. Limited proteolysis studies with proteinase-K further supported that manganese increases the stability of PrP C . Incubation of mouse brain slice cultures with manganese also resulted in increased prion protein levels and higher intracellular manganese accumulation. Furthermore, exposure of manganese to an infectious prion cell model, mouse Rocky Mountain Laboratory-infected CAD5 cells, significantly increased prion protein levels. Collectively, our results demonstrate for the first time that divalent metal manganese can alter the stability of prion proteins and suggest that manganese-induced stabilization of prion protein may play a role in prion protein misfolding and prion disease pathogenesis.

Although the prion protein is abundantly expressed in the CNS, its biological functions remain unclear. To determine the endogenous function of the cellular prion protein (PrP c ), we compared the effects of oxidative stress and endoplasmic reticulum (ER) stress inducers on apoptotic signaling in PrP c -expressing and PrP ko -knockout neural cells. H 2 O 2 , brefeldin-A (BFA) and tunicamycin (TUN) induced increases in caspase-9 and caspase-3, PKCδ proteolytic activation, and DNA fragmentation in PrP c and PrP ko cells. Interestingly, ER stress-induced activation of caspases, PKCδ, and apoptosis were significantly exacerbated in PrP c cells, whereas H 2 O 2 -induced proapoptotic changes were suppressed in PrP c compared to PrP ko cells. Additionally, caspases-12 and -8 were activated only in BFA and TUN treatments. Inhibitors of caspase-9, caspase-3, and PKCδ significantly blocked H 2 O 2 -, BFA-and TUN-induced apoptosis, whereas the caspase-8 inhibitor attenuated only BFAand TUN-induced cell death, and the antioxidant MnTBAP blocked only H 2 O 2 -induced apoptosis. Overexpression of the kinase inactive PKCδ K376R or the cleavage site-resistant PKCδ D327A mutants suppressed both ER-and oxidative stress-induced apoptosis. Thus, PrP c plays a proapoptotic role during ER stress, and an anti-apoptotic role during oxidative stress-induced cell death. Together, these results suggest that cellular PrP c enhances the susceptibility of neural cells to impairment of protein processing and trafficking, but decreases the vulnerability to oxidative insults, and that PKCδ is a key downstream mediator of cellular stress-induced neuronal apoptosis.

BackgroundPostoperative endocrine therapy is known to reduce recurrence and mortality in patients with estrogen receptor (ER)- or progestogen receptor (PR)-positive breast cancer. Correlates and determinants of compliance with endocrine therapy among Chinese patients with breast cancer are not known. The aim of this study was to elucidate the efficacy and adherence of endocrine therapy in China and suggest effective improvements on the adherence.Patients and methodsWe analyzed the survival of 1,110 patients eligible for endocrine therapy and adherence of 699 patients to endocrine therapy. Kaplan–Meier curves, log-rank tests and Cox proportional hazard models were used to evaluate survival, and logistic regression models were used to assess variables associated with treatment adherence.ResultsLong-term endocrine therapy was associated with lower recurrence rate (HR 0.72; 95% CI 0.56–0.93; p=0.013). Adherence to endocrine therapy was only 63.1%. Sociodemographic characteristics of patients, clinical- and medication-related characteristics and patients’ attitudes were associated with adherence to endocrine therapy.ConclusionAdherence to endocrine therapy in Chinese patients with ER+/PR+ breast cancer was <65%. Both patients and physicians should take progressive steps to improve the rate of adherence.

No abstract