RET activation by germline MEN2A and MEN2B mutations

Area of Science:

• Oncology
• Genetics
• Molecular Biology

Background:

• The RET proto-oncogene, encoding a receptor tyrosine kinase, is implicated in cancers and congenital disorders.
• Germline mutations in RET are linked to multiple endocrine neoplasia (MEN 2A/2B), familial medullary thyroid carcinoma (FMTC), and Hirschsprung disease (HSCR).

Purpose of the Study:

• To investigate the functional impact of specific RET proto-oncogene mutations associated with MEN 2A and MEN 2B.
• To compare the biochemical and biological activity of wild-type RET with MEN 2A and MEN 2B mutant forms.

Main Methods:

• Transfection of NIH3T3 and PC12 cells with MEN2A (Cys634->Arg) and MEN2B (Met918->Thr) RET constructs.
• Assessment of cell transformation and differentiation.
• Analysis of constitutive tyrosine phosphorylation and in vitro kinase activity.
• Immunoelectronmicroscopy to study RET clustering on cell surfaces.
• Comparison of wild-type and MEN 2B RET tyrosine kinase (TK) domain activity within RET/PTC oncogenes.

Main Results:

• MEN2A and MEN2B RET constructs induced NIH3T3 cell transformation and PC12 cell differentiation.
• Both mutant RET proteins exhibited constitutive tyrosine phosphorylation and significantly elevated in vitro kinase activity compared to wild-type.
• RET (MEN2A) with a Cys634->Trp mutation showed cell surface clustering.
• The MEN 2B mutation markedly increased the enzymatic activity of the RET TK domain in the context of RET/PTC.

Conclusions:

• Specific RET mutations, such as those in MEN 2A and MEN 2B, lead to constitutive activation and enhanced kinase function.
• RET activation through dimerization, particularly in RET/PTC oncogenes, is crucial for its full activity, even with pre-existing mutations like MEN 2B.
• These findings elucidate mechanisms underlying RET-driven cancers and congenital disorders.