SorLA signaling by regulated intramembrane proteolysis

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• The single-transmembrane receptor SorLA/LR11 plays a role in neuronal precursor cell proliferation.
• Neuropeptide head-activator enhances this proliferation in a SorLA-dependent manner.
• Head activator triggers SorLA shedding by TACE, releasing its extracellular domain.

Purpose of the Study:

• To investigate the processing of the remaining SorLA membrane fragment.
• To determine if gamma-secretase is involved in SorLA processing.
• To explore the functional consequences of SorLA cytoplasmic domain release.

Main Methods:

• Inhibition of gamma-secretase using specific inhibitors.
• Overexpression of dominant-negative presenilin mutants.
• Knockout of presenilin genes.
• In vitro cleavage assays.
• Analysis of SorLA cytoplasmic domain localization (fusion protein with EGFP).
• Reporter gene assays to assess transcriptional activity.

Main Results:

• Gamma-secretase processes the SorLA COOH-terminal membrane fragment.
• Inhibition or knockout of gamma-secretase leads to accumulation of SorLA membrane fragment and full-length SorLA.
• Gamma-secretase-dependent release of SorLA cytoplasmic domain and SorLA beta-peptide observed in vitro.
• Released SorLA cytoplasmic domain translocates to the nucleus if its nuclear localization signal is intact.
• SorLA cytoplasmic domain acts as a transcriptional activator in reporter gene assays.

Conclusions:

• SorLA undergoes gamma-secretase-dependent intramembrane cleavage, releasing its cytoplasmic domain.
• This processing is analogous to Notch receptor signaling.
• The released SorLA cytoplasmic domain can function as a transcriptional regulator, suggesting a novel signaling pathway.
• SorLA may directly regulate gene transcription following gamma-secretase activation.