Department of RNA Biology and Neuroscience, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Nat Commun. 2015 Jan 29;6:6183. doi: 10.1038/ncomms7183.
TAR DNA-binding protein of 43 kDa (TDP-43) and its C-terminal fragment of 25 kDa (CTF25) play critical roles in amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Although the overexpression of TDP-43 in cultured cells and animals results in the production of CTF25, the cleavage site that generates CTF25 and biological significance of the cleavage remain undetermined. Here we identify Asp174 as a cleavage site for CTF25. TDP-43 is cleaved initially after Asp174, which activates caspase-3/7 to accelerate TDP-43 fragmentation. Consequently, blockage of this cleavage results in a severe delay in TDP-43 clearance and prolonged necrotic cell death. We further show that the endoplasmic reticulum membrane-bound caspase-4 is the enzyme responsible for the cleavage after Asp174 and inhibition of caspase-4 activity slows TDP-43 fragmentation and reduces cell viability. These findings suggest that caspase-4-mediated cleavage after Asp174 is an initiator of TDP-43 clearance, which is required to avoid cell death induced by overexpressed TDP-43.
TAR DNA 结合蛋白 43kDa（TDP-43）及其 25kDa 的 C 末端片段（CTF25）在肌萎缩性侧索硬化症和额颞叶变性中发挥关键作用。虽然在培养细胞和动物中过表达 TDP-43 会导致产生 CTF25，但产生 CTF25 的切割位点和切割的生物学意义仍未确定。在这里，我们确定 Asp174 是 CTF25 的切割位点。TDP-43 最初在 Asp174 后被切割，这会激活半胱天冬酶-3/7 以加速 TDP-43 片段化。因此，阻断这种切割会导致 TDP-43 清除严重延迟和延长坏死性细胞死亡。我们进一步表明，内质网膜结合的半胱天冬酶-4 是负责 Asp174 后切割的酶，抑制半胱天冬酶-4 活性会减缓 TDP-43 片段化并降低细胞活力。这些发现表明，Asp174 后半胱天冬酶-4 介导的切割是 TDP-43 清除的启动子，这是避免过表达 TDP-43 诱导的细胞死亡所必需的。
