Cellular Prion Protein Regulates Its Own α-Cleavage through ADAM8 in Skeletal Muscle

Sergei Ilchenko,Wei Wang,Debra Sorensen,Sarah Medina,Stephanie A. Booth,Qingzhong Kong,Jingjing Liang,Witold K. Surewicz,Janna Kiselar

doi:10.1074/jbc.m112.360891

Sergei Ilchenko, Wei Wang + Show 7 more

Open Access

https://doi.org/10.1074/jbc.m112.360891

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Abstract

The ubiquitously expressed cellular prion protein (PrP(C)) is subjected to the physiological α-cleavage at a region critical for both PrP toxicity and the conversion of PrP(C) to its pathogenic prion form (PrP(Sc)), generating the C1 and N1 fragments. The C1 fragment can activate caspase 3 while the N1 fragment is neuroprotective. Recent articles indicate that ADAM10, ADAM17, and ADAM9 may not play a prominent role in the α-cleavage of PrP(C) as previously thought, raising questions on the identity of the responsible protease(s). Here we show that, ADAM8 can directly cleave PrP to generate C1 in vitro and PrP C1/full-length ratio is greatly decreased in the skeletal muscles of ADAM8 knock-out mice; in addition, the PrP C1/full-length ratio is linearly correlated with ADAM8 protein level in myoblast cell line C2C12 and in skeletal muscle tissues of transgenic mice. These results indicate that ADAM8 is the primary protease responsible for the α-cleavage of PrP(C) in muscle cells. Moreover, we found that overexpression of PrP(C) led to up-regulation of ADAM8, suggesting that PrP(C) may regulate its own α-cleavage through modulating ADAM8 activity.

Highlights

Endoproteolytic ␣-cleavage of cellular prion protein (PrPC) regulates PrPC toxicity and functions; the responsible protease(s) is uncertain
ADAM8 mRNA Level Is Up-regulated in Skeletal Muscle of Doxycycline-treated Tg(HQK) Mice—To investigate the protease(s) responsible for the ␣-cleavage of PrPC in skeletal muscles, Tg(HQK) mice with strictly Dox-dependent, skeletal muscle-specific expression of human PrP [59] were fed with Dox-laced food for 7, 14, 30, or 60 days; three animals were taken at each time point
Total RNA samples were isolated from skeletal muscle tissues and subjected to quantitative real time PCR analysis for the three ADAMs already implicated in the ␣-cleavage of PrPC (ADAM10, ADAM17, and ADAM9) as well as three other ADAMs (ADAM8, ADAM12, and ADAM23)

Summary

Background

Endoproteolytic ␣-cleavage of cellular prion protein (PrPC) regulates PrPC toxicity and functions; the responsible protease(s) is uncertain. ADAM8 can directly cleave PrP to generate C1 in vitro and PrP C1/fulllength ratio is greatly decreased in the skeletal muscles of ADAM8 knock-out mice; in addition, the PrP C1/full-length ratio is linearly correlated with ADAM8 protein level in myoblast cell line C2C12 and in skeletal muscle tissues of transgenic mice These results indicate that ADAM8 is the primary protease responsible for the ␣-cleavage of PrPC in muscle cells. The ␣-cleavage disrupts the PrP106 –126 region critical for both PrP toxicity and PrPC to PrPSc conversion [22,23,24,25] Both products of PrPC ␣-cleavage are biologically active: the N1 fragment is neuroprotective in vitro and in vivo by modulating the p53 pathway [31] while the C1. We present evidence to show that [1] ADAM8 can directly perform ␣-cleavage of PrP in vitro, [2] ADAM8 plays a major role in the ␣-cleavage of PrPC in muscle cells, and [3] overexpression of PrPC leads to elevated ADAM8 levels in muscle, suggesting a feedback loop where PrPC regulates its own ␣-cleavage through up-regulation of ADAM8

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