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).