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Mol. Cell. Biol., 02 1997, 799-808, Vol 17, No. 2
M Jeffers, GA Taylor, KM Weidner, S Omura and GF Vande Woude
The Met tyrosine kinase receptor is a widely expressed molecule which
mediates pleiotropic cellular responses following activation by its ligand,
hepatocyte growth factor/scatter factor (HGF/SF). In this communication we
demonstrate that significant Met degradation is induced by HGF/SF and that
this degradation can be blocked by lactacystin, an inhibitor of proteasome
activity. We also show that Met is rapidly polyubiquitinated in response to
ligand and that polyubiquitinated Met molecules, which are normally
unstable, are stabilized by lactacystin. Both HGF/SF-induced degradation
and polyubiquitination of Met were shown to be dependent on the receptor
possessing intact tyrosine kinase activity. Finally, we found that a
normally highly labile 55-kDa fragment of the Met receptor is stabilized by
lactacystin and demonstrate that it represents a cell- associated remnant
that is generated following the ligand-independent proteolytic cleavage of
the Met receptor in its extracellular domain. This truncated Met molecule
encompasses the kinase domain of the receptor and is itself tyrosine
phosphorylated. We conclude that the ubiquitin-proteasome pathway plays a
significant role in the degradation of the Met tyrosine kinase receptor as
directed by ligand- dependent and -independent signals. We propose that
this proteolytic pathway may be important for averting cellular
transformation by desensitizing Met signaling following ligand stimulation
and by eliminating potentially oncogenic fragments generated via
extracellular cleavage of the Met receptor.
Copyright © 1997, American Society for Microbiology
Degradation of the Met tyrosine kinase receptor by the ubiquitin- proteasome pathway
ABL-Basic Research Program, NCI-Frederick Cancer Research and Development Center, Maryland 21702, USA.
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