Untersuchungen zu der Entstehung und der Bedeutung löslicher Fragmente der neuralen Zelladhäsionsmoleküle NCAM und L1 im Zentralen Nervensystem der Maus
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Philipps-Universität Marburg
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Abstract
A variety of different membrane proteins also occur as a circulating, soluble form.
These soluble forms are often derived from the membrane forms by proteolysis.
Different soluble fragments of the transmembrane and multidomain neural cell
adhesion molecules NCAM and L1 playing important functional roles in the
developing and adult nervous system have been detected.
The mechanism of generation of soluble NCAM fragments with a molecular range
of 110 kDa to 190 kDa is poorly understood. In this study, evidence was
presented that a metalloprotease is able to solubilize NCAM fragments via
proteolytic processing. A member of the ADAM family of metalloproteases, the
TNFa converting enzyme (TACE) cleaves the NCAM isoforms NCAM140 and
NCAM180 near their membrane anchors resulting in the release of soluble NCAM
fragments with a molecular weight of 110 kDa and higher depending on the
glycosylation state of the extracellular domain of NCAM. The extracellular domain
of the GPI-linked isoform NCAM120 is liberated from the membrane via a different
mechanism. The metalloprotease inhibitor GM 6001 reduces the release of
soluble NCAM fragments. Its inhibitory effect on NCAM dependent neurite
outgrowth of cerebellar explants indicates that the proteolytic processing of NCAM
plays an important role for NCAM dependent neurite outgrowth. Further evidence
for an essential role of the ectodomain shedding of NCAM for the process of
NCAM dependent neurite outgrowth was obtained in experiments showing that the
calmodulin inhibitor CGS 9343 B which is able to stimulate the cleavage of
membrane bound NCAM isoforms, inhibits NCAM dependent neurite outgrowth.
Whether the effect of calmodulin on NCAM dependent neurite outgrowth is
mediated via a direct interaction with its binding partner NCAM remains to be
clarified.
The cell adhesion molecule L1 is proteolytically processed at two distinct sites
within the extracellular domain, leading to the generation of different soluble
fragments. Evidence was presented that the proprotein convertase PC5A is the
protease that cleaves L1 in the third fibronectin type III domain, whereas the
proprotein convertases furin, PC1, PC2, PACE4, and PC7 are not effective in
cleaving L1. This fragment was present in the hippocampus, which expresses
PC5A, but was not detectable in the cerebellum, which does not express PC5A.
The 140 kDa L1 fragment was found to be tightly associated with the full-length
200 kDa L1 molecule. The complex dissociated from the membrane upon
cleavage by a protease acting at a more membrane-proximal site of full-length L1.
This proteolytic cleavage was inhibited by the metalloprotease inhibitor GM 6001
and enhanced by a calmodulin inhibitor. L1-dependent neurite outgrowth of
cerebellar neurons was inhibited by GM 6001, suggesting that proteolytic
processing of L1 by a metalloprotease is involved in neurite outgrowth. In this
study, it was shown that L1 is processed at further proteolytic cleavage sites in its
extracellular domain resulting in the release of additional soluble fragments. The
metalloprotease MMP9 seems to be one the responsible proteases involved in
this process. A lot of transmembrane proteins were identified to be additionally
cleaved within their transmembrane domains. The ectodomain shedding of the
extracellular domain is the initial step for regulated intramembranous proteolysis.
A 15 kDa fragment recognized by an antibody directed against the intracellular
domain of L1 is released from the plasma membrane into the cytoplasm via
proteolysis and transported to the nucleus. The question whether the intracellular
domain of L1 located in the nucleus is involved in regulation of gene transcription
is currently under investigation.
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Dates
Created: 2005Issued: 2005-04-07Updated: 2011-08-10
Faculty
Medizin
Publisher
Philipps-Universität Marburg
Language
ger
Data types
DoctoralThesis
Keywords
Central nervous systemNeuritenwachstumNCAMNeural cell adhesion moleculeNeurite outgrowthKernlokalisierungProhormonkonvertasenRegulated intramembranous proteolysis (RIP)Proteolytic processingL1
DFG-subjects
MetalloproteinasenNeurales Zell-AdhäsionsmolekülZentralnervensystemProzessierungCalmodulin
DDC-Numbers
610
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Kalus, Ina (129997951): Untersuchungen zu der Entstehung und der Bedeutung löslicher Fragmente der neuralen Zelladhäsionsmoleküle NCAM und L1 im Zentralen Nervensystem der Maus. : Philipps-Universität Marburg 2005-04-07. DOI: https://doi.org/10.17192/z2005.0203.
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This item has been published with the following license: In Copyright