Several Proteintech antibodies have recently appeared in an Acta Neuropathologica paper further distinguishing the pathomechanisms behind FTLD-FUS and ALS with FUS mutations (ALS-FUS) . The paper results from an international collaboration of several labs — including those of neuropathology experts Manuela Neumann (Tübingen, Germany) and Ian Mackenzie (Vancouver, Canada). The work describes differences in the pathomechanisms contributing to FTLD-FUS and ALS-FUS, two neurodegenerative diseases sharing overlapping pathologies.
FUS (short for fused in sarcoma) accumulates in the cytoplasm of neurons and glia in both ALS- and FTLD-FUS, forming inclusions. FUS inclusions are a hallmark of both FTLD-FUS and ALS-FUS, but despite this, distinct differences in the composition of their proteins and underpinning mechanisms are becoming increasingly apparent.
Previous immunohistochemical studies in Neumann’s lab revealed that ALS-FUS inclusions stain exclusively for FUS, whereas FTLD-FUS inclusions also stain for TAF15 and EWS. These results were published in Brain, featuring Proteintech’s monoclonal FUS antibody . The FUS gene harbors mutations in ALS-FUS, yet remains intact in FTLD-FUS making it unlikely that FUS is the direct cause of its own exclusion from the nucleus in the latter case.
All three FET protein family members, FUS, Ewing’s sarcoma (EWS) protein and TATA-binding protein associated factor 15 (TAF15), are nucleocytoplasmic shuttling proteins; they regularly cross between their dominant location in the nucleus and the cytoplasm to carry out their roles in RNA transcription, processing and transport. Transportin (Trn1) is a nuclear import protein that facilitates FET protein re-entry to the nucleus. Neumann et al. also found Trn1 in FTLD-FUS neuronal and glial inclusions. Correspondingly, no Trn1 was found in ALS-FUS inclusions.
Trn1 recognizes a nuclear localization signal called PY-NLS on the FET proteins and this is required for their nuclear transport. It is this same sequence that is mutated in FUS in the case of ALS-FUS, disrupting its re-location to the nucleus. So how does Trn1 get involved in FTLD-FUS inclusion formation if PY-NLS is still intact in this case? Several other cargo proteins also possess this signal sequence as well, such as hnRNPD and hnRNPH1, SAM68 and RBM39. So were they also found in FTLD-FUS inclusions?
Neumann and colleagues assessed the questions above using several Proteintech antibodies among others – including PQBP-1, SLM-2 and HEXIM1. In total they looked at thirteen other PY-NLS-containing proteins and whether they were involved in FTLD-FUS inclusions; however, they could find no evidence of any abnormal accumulation or alterations in their subcellular distribution. As the nuclear transport of these other proteins is unaffected, it seems no primary defect in Trn1 itself could be responsible for FET protein accumulation – so what else could?
A current hypothesis is that abnormal posttranslational modifications (PTMs), that specifically affect FET proteins, play a role in FTLD and ALS. There are several PTMs described in the existing literature, including phosphorylation and arginine methylation, shown to affect cellular distribution, RNA/DNA binding ability, protein-protein interaction, and protein stability of the FET proteins. Evidence of FUS methylation re-routing the protein to the cytoplasm was presented by Dorothee Dormann at the 8th International Frontotemporal Dementia (FTLD) Meeting, held in Manchester (UK) this month. Dormann, based in the lab of Christian Haass at the Ludwig-Maximilians-Universität in Munich, Germany, investigated arginine methylation of FUS and its influence on FUS localization using HeLa cells expressing FUS NLS mutants. In the presence of AdOx, a broad-spectrum methylation inhibitor, the FUS NLS mutants switched back to a nuclear location in HeLa cells, despite their PY-NLS mutations . The finding suggests that methylation plays an important role in FUS retention in the cytoplasm than previously thought. Further work confirmed that these methylations interfere with FUS binding to Trn1 — whether this is true for the other FET proteins remains to be seen.
 M. Neumann et al., Acta Neuropathologica 2012 [epub ahead of print].
 M. Neumann et al., Brain 2011; 134(9): 2595–2609.
 D Dormann et al., EMBO J 2012 [epub ahead of print].
EWS - 55191-1-AP – rabbit polyclonal – ELISA, WB
FUS -60160-1-Ig – mouse monoclonal – ELISA, WB, IHC, IF
hnRNPD - 12770-1-AP – rabbit polyclonal – ELISA, WB, IHC, IF
hnRNPH1 - 14774-1-AP – rabbit polyclonal – ELISA, WB, IHC
HEXIM1 - 15676-1-AP – rabbit polyclonal – ELISA, WB, IF
PQBP-1 - 16264-1-AP – rabbit polyclonal – ELISA, WB
RBM39 - 21339-1-AP – rabbit polyclonal – ELISA, WB, IHC
SAM68 - 10222-1-AP – rabbit polyclonal - ELISA, WB, IHC, IF
SLM-2 - 13563-1-AP – rabbit polyclonal - ELISA, WB, IHC