THE MULTIPLE ENDOCRINE NEOPLASIA TYPE 2B POINT MUTATION ALTERS LONG-TERM REGULATION AND ENHANCES THE TRANSFORMING CAPACITY OF THE EPIDERMALGROWTH-FACTOR RECEPTOR

The RET proto-oncogene encodes a member of the receptor tyrosine kinas e family, Multiple endocrine neoplasia type 2B (MEN 2B) is caused by t he mutation of a conserved methionine to a threonine in the catalytic domain of the RET kinase, When the MEN 2B point mutation was introduce d into the epidermal growth factor (EGF) receptor (M857T EGFR), the in trinsic tyrosine kinase activity of the mutant receptor was similar to that of wild-type EGF receptor and remained ligand-dependent, However , the mutant receptor showed an enhanced transforming capacity compare d to the wild-type receptor as judged by its ability to mediate the gr owth of NIH 3T3 cells in soft agar. Using the oriented peptide library approach to examine substrate specificity, the M857T mutation was fou nd to be associated with a decrease in the selectivity of the receptor for Phe and an increase in the selectivity for acidic residues at the P + 1 position as compared to wild-type EGF receptor, Short-term resp onses to EGF were similar in cells expressing wild-type and M857T EGF receptors. However, significant differences in receptor down-regulatio n were observed between the two receptors. These data demonstrate that the MEN 2B point mutation alters the substrate specificity of recepto r tyrosine kinases and suggest that the enhanced oncogenesis associate d with the MEN 2B mutation may be due in part to alterations in recept or regulation.