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Document 0964
DOCN M9460964
TI Post-translational modifications of the env-sea tyrosine kinase and
their role in transformation.
DT 9406
AU Crowe AJ; State Univ. of New York at Stony Brook
SO Diss Abstr Int [B]; 54(5):2356 1993. Unique Identifier : AIDSLINE
ICDB/94698736
AB Analysis of the oncogenic counterparts of receptor tyrosine kinases has
enabled researchers to study how oncoproteins transform cells, as well
as to gain insights into the signal transduction pathway initiated by
receptors in normal cells. V-sea is a member of the growth factor
receptor family of tyrosine kinases. Our analysis of the intracellular
processing of the sea oncoprotein indicates that v-sea, like other
retroviral env proteins and growth factor receptors such as the insulin
receptor and the hepatocyte growth factor receptor (c-met), encodes a
precursor protein which undergoes proteolytic processing and terminal
glycosylation in the Golgi to yield the complex carbohydrate forms which
are then transported to the cell surface. Both mutagenesis and
glycosylation inhibitors were employed to determine the role of post
translational modifications of v-sea in transformation. First,
mutagenesis of the invariant lysine residue in the ATP-binding domain
confirmed that tyrosine kinase activity is necessary for v-sea-mediated
transformation. Secondly, replacement of the env domain of v-sea with a
myristylation signal indicated that the envelope domain itself was not
essential for transformation by v-sea, but may be necessary to target a
transformation-competent form of the tyrosine kinase to the membrane. In
addition, characterization of two cleavage mutants in v-sea has
determined that proteolytic processing to the mature gp70env-sea form is
not essential for transport, tyrosine kinase activity, or transformation
by v-sea. These results suggest that, in the absence of gp70env-sea a
terminally glycosylated uncleaved precursor is transported to the cell
surface and can functionally substitute for gp70env-sea as a
transforming protein. Inhibiting the formation of these cell surface
forms, either by shifting to the restrictive temperature for the ts-sea
oncogene, or by treatment with the glycosylation inhibitor
castanospermine, causes v-sea transformed cells to revert to a normal
phenotype. Together, our data support a model in which both tyrosine
kinase activity and correct cell surface localization are necessary for
transformation by v-sea, while proteolytic processing and terminal
glycosylation are not. However, these latter two processes may serve to
stabilize the correct conformation of the v-sea protein, thus ensuring
its efficient transport to and expression at the cell surface. (Full
text available from University Microfilms International, Ann Arbor, MI,
as Order No. AAD93-28178)
DE Cell Transformation, Neoplastic/GENETICS Gene Products, env/*METABOLISM
Glycosylation Hepatocyte Growth Factor/METABOLISM Mutagenesis
Oncogene Proteins, Viral/*METABOLISM *Protein Processing,
Post-Translational Protein-Tyrosine Kinase/METABOLISM Proto-Oncogene
Proteins/GENETICS/METABOLISM Receptor Protein-Tyrosine
Kinase/GENETICS/METABOLISM THESIS
SOURCE: National Library of Medicine. NOTICE: This material may be
protected by Copyright Law (Title 17, U.S.Code).