Biological Properties of Ret with Cysteine Mutations Correlate with Multiple Endocrine Neoplasia Type 2A, Familial Medullary Thyroid Carcinoma, and Hirschsprung's Disease Phenotype1

We investigatedthe transformingactivityofthe ret proto-oncogenewith a mutation in cysteine 609, 611, 618, 620, 630, or 634 detected in patients with multiple endocrine neoplasia type 2A (MEN 2A), familial meduilary thyroid carcinoma (FMTC), or Hirschsprung's disease. Of these cysteine mutations, codon 634 mutations are known to he correlated with the development of MEN 2A, whereas codon 609, 618, or 620 mutations were detected in two thirds of FMTCs and in several cases of Hirschsprung's disease. Analysis of a totalof 18mutantgenes revealedthatcodon634 mutationshavethe highest transforming activity. The activity of ret with a codon 609, 611, 618, or 620 mutation and with a codon 630 mutation was approximately 3to 5-fold and 2-fold lower than that of ret with a codon 634 mutation, respectively. In addition, different amino acid substitutions for the same cysteine displayed comparable transforming activity. The expression of the cell surface form of Ret with codon 609, 611, 618, or 620 mutationwas very low comparedwith that of Ret with codon 634 mutation, indicating that the former four muta lions might impairtransportof Ret to the plasmamembrane,as observedfor several Hirschspnmg mutations affecting the Ret extracellular domain. These results thus suggest that mutations in cysteine 609, 611, 618, or 620 may have the potential to develop Hirschsprung'sdisease in addition to MEN 2A and FMTC.