Characterization of the RET protooncogene transmembrane domain mutation S649L associated with nonaggressive medullary thyroid carcinoma.

Abstract

Context: For rare and novel RET mutations associated with hereditary medullary thyroid carcinoma (MTC), clinical and functional studies are needed to classify the RET mutation into one of the three clinical risk groups. Objective: We analyzed proliferative properties and clinical implications associated with the RET protooncogene transmembrane domain mutation S649L. Design: The transforming potential and mitogenic properties of S649L mutation were investigated clinically and by evaluating kinase activity, cell proliferation, and colony formation. Patients: Fifteen individuals from five kindreds were identified as carriers of a RET protooncogene mutation in exon 11 codon 649 (TCG Ser /TTG Leu ). In two out of five index patients, a second RET mutation (C634W or V804L) was detected. Results: Eight gene carriers were operated on. Histology revealed MTC and C-cell hyperplasia in three index and three screening patients respectively. In all other gene carriers (aged 41-64 years), calcitonin levels were in the normal range, and pentagastrin-stimulated calcitonin levels were !100 pg/ml. Therefore, thyroidectomy had not yet been performed. In one index patient carrying the S649L mutation, hyperparathyroidism was confirmed histologically. RET S649L-expressing NIH3T3 cells exhibited a clear increase of phosphotyrosine and proliferation rate when compared with parental NIH3T3 cells but a significantly lower kinase activity and cell growth rate when compared with RET C634R-expressing cells. When compared with RET C634R, the S649L mutant showed moderate transforming potential with small-sized colonies. Conclusions: Our clinical and in vitro findings indicate that the transmembrane RET S649L mutation is associated with late-onset non-aggressive disease. Recommendations for prophylactic thyroidectomy should be individualized depending on stimulated calcitonin levels.European Journal of Endocrinology 158 811-816

In vitro transforming potential, intracellular signaling properties, and sensitivity to a kinase inhibitor (sorafenib) of RET proto-oncogene variants Glu511Lys, Ser649Leu, and Arg886Trp

“…2C and D). These findings are consistent with other studies that have previously addressed and concordantly showed that these variants have a relatively modest transforming activity (Colombo-Benkmann et al 2008, Muzza et al 2010. A noteworthy observation was that despite transformation induced by variant Glu511Lys was modest, it was highly augmented by GDNF treatment (Fig.…”

Assessing the effect of RET Transmembrane Domain Mutations in receptor self-association capability using the in vivo TOXCAT System

“…However, only two out of five in silico prediction tools consider p.Ser649Leu as pathogenic or probably damaging mutation. Nevertheless, p.Ser649Leu variant is known to be a MEN2 causative mutation resulting in a medium aggressive MTC [18]. In case of p.Ala641Ser, one out of five in silico tools predicted it as possibly pathogenic [25].…”

“…The latter belongs to rare RET TMD mutations occurring as a double mutation in combination with other mutations or as a sole mutation in several MTC positive individuals throughout the world. However, the molecular mechanism, by which this mutation activates RET has not been elucidated [17][18][19]. The aim is to gain evidence required for better understanding of genotype: phenotype correlation in case of these two mutations, as well as to examine the possibility of establishing TOXCAT system for TMD interaction analyses in molecular oncology.…”

Genotype-phenotype relationship in multiple endocrine neoplasia type 2. Implications for clinical management

“…an abnormal CT response to pentagastrin or calcium stimulation). Further studies, especially in the rare mutations, 18 are necessary before more specific recommendations can be made (Table 3).…”