Studies on amyloid beta (Ab|), the peptide thought to play a crucial role in the pathogenesis of Alzheimer's disease, have implicated mitochondria in Ab-mediated neurotoxicity. We used differentiated PC12 cells stably transfected with an inducible green fluorescent protein (GFP) fusion protein containing an N¢-terminal mitochondrial targeting sequence (mtGFP), to examine the effects of sub-lethal Ab on the import of nuclear-encoded proteins to mitochondria. Exposure to sub-lethal Ab 25-35 (10 lmol/L) for 48 h inhibited mtGFP import to mitochondria; average rates decreased by 20 ± 4%. Concomitant with the decline in mtGFP, cytoplasmic mtGFP increased significantly while mtGFP expression and intramitochondrial mtGFP turnover were unchanged. Sub-lethal Ab 1-42 inhibited mtGFP import and increased cytoplasmic mtGFP but only after 96 h. The import of two endogenous nuclear-encoded mitochondrial proteins, mortalin/mtHsp70 and Tom20 also declined. Prior to the decline in import, mitochondrial membrane potential (mmp), and reactive oxygen species levels were unchanged in Ab-treated cells versus reverse phase controls. Sustained periods of decreased import were associated with decreased mmp, increased reactive oxygen species, increased vulnerability to oxygen-glucose deprivation and altered mitochondrial morphology. These findings suggest that an Ab-mediated inhibition of mitochondrial protein import, and the consequent mitochondrial impairment, may contribute to Alzheimer's disease.

. Calcineurinindependent regulation of plasma membrane Ca 2ϩ ATPase-4 in the vascular smooth muscle cell cycle. Am J Physiol Cell Physiol 285: C88-C95, 2003; 10.1152/ajpcell.00518.2002.-Calcineurin mediates repression of plasma membrane Ca 2ϩ -ATPase-4 (PMCA4) expression in neurons, whereas c-Myb is known to repress PMCA1 expression in vascular smooth muscle cells (VSMC). Here, we describe a novel mouse VSMC line (MOVAS) in which 45 Ca efflux rates decreased 50%, fura 2-AM-based intracellular Ca 2ϩ concentrations ([Ca 2ϩ ]i) increased twofold, and real-time RT-PCR and Western blot revealed a ϳ40% decrease in PMCA4 expression levels from G 0 to G1/S in the cell cycle, where PMCA4 constituted ϳ20% of total PMCA protein. Although calcineurin activity increased fivefold as MOVAS progressed from G0 to G1/S, inhibition of this increase with either BAPTA or retroviral transduction with peptide inhibitors of calcineurin (CAIN), or its downstream target nuclear factor of activated T cells (NFAT) (VIVIT), had no effect on the repression of PMCA4 mRNA expression at G1/S. By contrast, Ca 2ϩ -independent activity of the calmodulin-dependent protein kinase-II (CaMK-II) increased eightfold as MOVAS progressed from G0 to G1/S, and treatment with an inhibitor of CaMK-II (KN-93) or transduction of a c-Myb-neutralizing antibody significantly alleviated the G1/S-associated repression of PMCA4. These data show that G1/S-specific PMCA4 repression in proliferating VSMC is brought about by c-Myb and CaMK-II and that calcineurin may regulate cell cycle-associated [Ca 2ϩ ]i through alternate targets. /calmodulin-mediated signals act at multiple points in the cell cycle, including the G 0 /G 1 transition, the initiation of S-phase, and the initiation and completion of M phase (reviewed in Refs. 4,31,38,and 44 ] i ) needed for G 1 -to-S transitions in rat vascular smooth muscle cells (VSMC) (22, 23).We previously showed that the cell cycle-associated repression of PMCA1 expression during G 0 to G 1 /S progression in rat VSMC is mediated by the c-Myb transcription factor (1). However, the mechanism(s) underlying the cell cycle-associated repression of PMCA4 had not been elucidated. Guerini et al. (18) demonstrated in mouse neurons that PMCA4 expression can be repressed by a calcineurin-dependent pathway. Given this result, we hypothesized that G 1 /Sassociated repression of PMCA4 expression in VSMC may also be mediated by calcineurin. To explore these mechanisms in cell culture, we generated a clonal, immortalized mouse VSMC line (MOVAS). Immunostaining for smooth muscle-specific proteins such as SM22␣, calponin, smooth muscle-specific ␣-actin and desmin, as well as SM22␣ promoter-driven enhanced green fluorescent protein (EGFP) expression, confirm the lineage and phenotype of these cells. 45 Ca efflux assays and fura 2-based ratiometric Ca 2ϩ imaging reveal regulated Ca 2ϩ efflux and [Ca 2ϩ ] i at the G 1 /S transition point. Western blot and real time RT-PCR reveal cell cycle-regulated repression of mouse PMCA1 and PMCA4. Drugs in...

Disturbances of endoplasmic reticulum (ER) Ca2ϩ homeostasis or protein processing can lead to ER stress-induced cell death. Increasing evidence suggests that oxidative stress (OS) plays an important role in a variety of cell death mechanisms. To investigate the role of OS in ER stress, we measured OS in response to three ER stress agents: econazole (Ec), which stimulates ER Ca 2ϩ release and blocks Ca 2ϩ influx; thapsigargin (Tg), a sarco(endo)plasmic reticulum Ca 2ϩ ATPase inhibitor that releases ER Ca 2ϩ and stimulates Ca 2ϩ influx; and tunicamycin (Tu), a glycosylation inhibitor that causes protein accumulation in the ER. Ec, but not Tg or Tu, caused a rapid increase in OS. Reactive oxygen species (ROS) generation was observed within mitochondria immediately after exposure to Ec. Furthermore, Ec hyperpolarized the mitochondrial membrane and inhibited adenine nucleotide transport in cell-free mitochondria, suggesting a mitochondrial target. Antimycin A, an inhibitor of complex III in electron transport, reversed mitochondrial hyperpolarization, OS generation, ER Ca 2ϩ depletion, and cell death by Ec, suggesting complex III dependence for these effects. Antioxidants butylated hydroxytoluene and NAcetyl-L-cysteine prevented ER Ca 2ϩ depletion and cell death by Ec. However, inhibition of Ca 2ϩ influx by Ec was unaffected by either antimycin A or the antioxidants, suggesting that this target is distinct from the mitochondrial target of Ec. Atractyloside, an adenine nucleotide transport inhibitor, generated ROS and stimulated ER Ca 2ϩ release, but it did not block Ca 2ϩ influx, deplete the ER or induce cell death. Taken together, these results demonstrate that combined mitochondrial ROS generation and Ca 2ϩ influx blockade by Ec is required for cell death.