Human
glioma cells frequently overexpress
epidermal growth factor receptor (EGFR). We found that the CrkII proto-oncogene product was associated with the EGFR in human
glioma cells in the absence of
epidermal growth factor (
EGF).
EGF stimulation of
glioma cells induced the phosphorylation of
tyrosine 221 of the
CrkII protein, which correlates with its dissociation from the EGFR. By contrast, Shc and Grb2 were inducibly associated with the EGFR in response to
EGF stimulation of
glioma cells. In A431 cells,
epidermoid carcinoma cells which overexpress EGFR, CrkII was
tyrosine-phosphorylated and associated with the EGFR in an
EGF-dependent manner. Therefore, the dissociation of CrkII from the EGFR upon stimulation with
EGF appears to be specific to
glioma cells. The Cbl
oncogene product was also
tyrosine-phosphorylated in U87MG
glioma cells upon
EGF stimulation. However, unlike in other cell lines, CrkII was not inducibly bound to Cbl in U87MG
glioma cells. Thus,
EGF-dependent binding of CrkII to
phosphotyrosine-containing
proteins appears to be suppressed in
glioma cells. To evaluate the physiological role of dissociation of CrkII from EGFR, we expressed the CrkII-23 mutant in
glioma cells. CrkII-23 mutant, which was isolated as a suppressor gene of the
EGF-dependent transformation of NRK cells, binds constitutively to EGFR. We found that expression of CrkII-23 inhibited the anchorage-independent growth of the
glioma cells in the presence of
EGF. Taken together, these data implicate
EGF-dependent dissociation of CrkII from EGFR in the oncogenicity of human
glioma cells.