Amyotrophic lateral sclerosis-associated proteins TDP-43 and FUS/TLS function in a common biochemical complex to co-regulate HDAC6 mRNA

Department of Pharmacology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin 53706, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 10/2010; 285(44):34097-105. DOI: 10.1074/jbc.M110.154831
Source: PubMed

ABSTRACT Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease that preferentially targets motor neurons. It was recently found that dominant mutations in two related RNA-binding proteins, TDP-43 (43-kDa TAR DNA-binding domain protein) and FUS/TLS (fused in sarcoma/translated in liposarcoma) cause a subset of ALS. The convergent ALS phenotypes associated with TDP-43 and FUS/TLS mutations are suggestive of a functional relationship; however, whether or not TDP-43 and FUS/TLS operate in common biochemical pathways is not known. Here we show that TDP-43 and FUS/TLS directly interact to form a complex at endogenous expression levels in mammalian cells. Binding was mediated by an unstructured TDP-43 C-terminal domain and occurred within the context of a 300-400-kDa complex that also contained C-terminal cleavage products of TDP-43 linked to neuropathology. TDP-43 C-terminal fragments were excluded from large molecular mass TDP-43 ribonucleoprotein complexes but retained FUS/TLS binding activity. The functional significance of TDP-43-FUS/TLS complexes was established by showing that RNAi silencing of either TDP-43 or FUS/TLS reduced the expression of histone deacetylase (HDAC) 6 mRNA. TDP-43 and FUS/TLS associated with HDAC6 mRNA in intact cells and in vitro, and competition experiments suggested that the proteins occupy overlapping binding sites. The combined findings demonstrate that TDP-43 and FUS/TLS form a functional complex in intact cells and suggest that convergent ALS phenotypes associated with TDP-43 and FUS/TLS mutations may reflect their participation in common biochemical processes.

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    • "FUShasbeenreportedtoco-localizewithTDP-43innuclear complexes(Kimetal.,2010b;Lingetal.,2010)andinlarger cytoplasmiccomplexes(Kimetal.,2010b).PurifiedFUShas alsobeenreportedtointeractwithpurifiedHis-taggedTDP- 43invitroinanRNA-independentmanner,associatedtothe C-terminalregionofTDP-43(Kimetal.,2010b).Theseubiq- uitouslyexpressedbindingproteinsseemtohavesimilarand complementaryfunctions. OnlythemutantformofFUSwasfoundinstressgranules inreponsetotranslationalarrest(Boscoetal.,2010).FUSand TDP-43wereobservedtoco-localizeincytoplasmicaggregations ofALS/FTLD-affectedneurons(DaCruzandCleveland,2011). "
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    • "One possibility explaining the less severe effects we observe upon expression of wild-type TDP-43 is that wild-type TDP-43 autodownregulates the expression of endogenous TDP-43 (tbph), thus compensating for the increased HDAC6 levels (Ayala et al., 2011). Another possibility is that the pathogenic TDP43 proteins localize differently in comparison to the wild-type TDP-43, harboring additional or stronger effects on HDAC6 mRNA (Estes et al., 2011; Kim et al., 2010). The extent to which either of these mechanisms is at play in fly motor neurons needs to be further explored in the future. "
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    • "Nevertheless, evidence of the role of HDAC6 in ALS is emerging. In a recent work it was found that TDP43 and fused in sarcoma/translated in liposarcoma (FUS/TLS), which are proteins that regulate RNA processing and have been found to be mutated in some cases of ALS, interact with each other forming a ribonucleoprotein complex that regulates the expression of HDAC6 through its mRNA stability (Kim et al., 2010). Class IV HDAC only member, HDAC11, is localized in the cell nucleus and is structurally different from the other classes (Kazantsev and Thompson, 2008). "
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