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Evidence for autocrine activation of a tyrosine kinase in a human gastric carcinoma cell line
Author(s) -
Giordano Silvia,
Renzo Maria Flavia Di,
Narsimhan Radha P.,
Tamag Luca,
Gerbaudo Elena V.,
ChiadóPiat Loredana,
Comoglio Paolo M.
Publication year - 1988
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.240380402
Subject(s) - tyrosine phosphorylation , receptor tyrosine kinase , tyrosine kinase , phosphorylation , tyrosine , autocrine signalling , sh2 domain , autophosphorylation , biology , cancer research , platelet derived growth factor receptor , microbiology and biotechnology , chemistry , receptor , growth factor , biochemistry , protein kinase a
Phosphotyrosine (P‐Tyr) antibodies have been used to identify the phosphorylated forms of growth factor receptors and oncogene‐coded tyrosine kinases. Western blot analysis of a gastric carcinoma cell line with P‐Tyr antibodies revealed a tyrosine‐phosphorylated protein of M r 145,000 (P145). In addition, in vitro phosphorylation with (γ‐ 32 P)ATP of P‐Tyr immunoprecipitates of the same cells resulted in labelling of this protein on tyrosine. P145 appears to be a transmembrane glycoprotein, with features suggestive of a growth factor receptor. However, the in vivo or in vitro addition of known growth factors did not affect P145 tyrosine phosphorylation. We now report that P145 is rapidly dephosphorylated in vivo when cells are exposed to low pH, a condition known to dissociate ligands from their receptors. The addition of serum‐free medium, conditioned by the gastric carcinoma cells, fully restores the tyrosine phosphorylation lost with acid treatment. These data suggest that the activity responsible for P145 phosphorylation on tyrosine, whether intrinsic to P145 itself or due to an associated kinase, is stimulated by a factor secreted by the tumor cells themselves.

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