MECHANISM OF RET DYSFUNCTION BY HIRSCHSPRUNG MUTATIONS AFFECTING ITS EXTRACELLULAR DOMAIN

Hirschsprung disease (HSCR) is a congenital disorder associated with t he absence of intrinsic ganglion cells in the distal gastrointestinal tract, Recently, many missense, nonsense and frameshift mutations of t he ref proto-oncogene were found in familial and sporadic cases of HSC R, Consistent with the view that the HSCR phenotype is the result of i nactivation of Ret, the missense mutations detected in the tyrosine ki nase domain were demonstrated to result in a marked decrease of the ki nase activity of Ret, However, the effects of missense mutations found in the extracellular domain remain unknown, We now report that five m utations in the extracellular domain examined inhibit transport of the Ret protein to the plasma membrane, As a consequence, they significan tly decreased the transforming activity of Ret with multiple endocrine neoplasia (MEN) 2A mutation for which cell surface expression is requ ired, Our results also demonstrated that long segment HSCR mutations m ore severely impair transport of Ret to the plasma membrane than a sho rt segment HSCR mutation, suggesting that the level of its cell surfac e expression may correlate to the HSCR phenotype.