Targeting of cytosolic PrP^ via a novel 14-3-3-Tom 70-mitochondrial BCL-2 pathway induces mitochondrial apoptosis
Naomi S. Hachiya, Makiko Yamada, Kota Watanabe, Akiko Jozuka, Yo- shimichi Kozuka, Yuji Sakasegawa and Kiyotoshi Kaneko
Dept. Cortical Func. Disorders, Natl. Inst. Neurosci., Natl. Center Neurol.
Psychiat., CREST, JST, 4-1-1 Ogawa-Higashi, Kodaira, Tokyo 187-8502 Japan <e-mail> naomi@ncnp.go.jp
Abstract
Transgenic mice harboring a high-copy-number of wild-type mouse (Mo) cellular prion protein (PrP^) are known to develop a spontaneous neuro- logical dysfunction in an age-dependent manner, even without inoculation of the scrapie isoform of prion protein (PrP^^). Here we first demonstrate mitochondria-mediated apoptosis in aged transgenic mice overexpressing wild-type MoPrP^. These mice remained healthy, and no neuropa- thological abnormality was observed, however, exhibited an aberrant mi- tochondrial localization of PrP^ concomitant with decreased proteasome activity, while younger littermates did not. Such aberrant mitochondrial localization of PrP^ was accompanied by cytochrome c release into the cytosol, caspase-3 activation, and DNA fragmentation, most predomi- nantly in hippocampal pyramidal cells. Next, we reconstituted these re- sults using cell culture system. When neuronal (N2a) culture cells ex- pressing wild-type PrP^ were used in combination with proteasome inhibitors, PrP^ targeted to mitochondria and several apoptotic phenome- non was observed. Furthermore, using the assay system, we revealed a novel mitochondrial PrP-related apoptotic pathway as follows. First, we found that PrP residues 122-139 required for the mitochondrial targeting and 14-3-3 protein worked as a transporter of PrP^ to Tom70, a mitochon- drial outer membrane receptor for mitochondrial precursor proteins.
Second, we show for the first time that TomTO is involved in mitochon- drial apoptosis, and thus plays a pivotal role in cell survival and death.
Third, PrP^ thereafter binds BCL-2 on the mitochondrial outer membrane and subsequently induces mitochondrial apoptosis. Our data indicate that
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