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Distinct biological properties of two RET isoforms activated by MEN 2A and MEN 2B mutations
M Rossel1, A Pasini, S Chappuis
1Laboratoire de Génétique, UMR 5641 CNRS, Domaine Rockfeller, Université Claude Bernard Lyon, France.
Abstract:
Germline mutations of the RET proto-oncogene, which codes for a receptor tyrosine kinase, cause multiple endocrine neoplasia type 2A (MEN 2A) and 2B (MEN 2B) and familial medullary thyroid carcinoma (FMTC). MEN 2 mutations have been shown to result in RET oncogenic activation. The RET gene encodes several isoforms whose biological properties, when altered by MEN 2 mutations, have not been thoroughly addressed yet. In this study, we have introduced a MEN 2A mutation (Cys634-->Arg) and the unique MEN 2B mutation (Met918-->Thr) in two RET isoforms of 1114 and 1072 amino acids which differ in the carboxy-terminus part. Herein, we report that each RET isoform activated by MEN 2A or MEN 2B mutation was transforming in fibroblasts and induced neuronal differentiation of pheochromocytoma PC12 cells. However, among the different RET-MEN 2 mutants, the long RET isoform activated by the MEN 2B mutation stimulated the most prominent neurite outgrowth in PC12 cells, while the short RET isoform counterpart elicited a very weak differentiation effect in PC12 cells. We further demonstrate that the morphological changes of PC12 cells caused by constitutively activated RET oncoproteins involved the engagement of a Ras-dependent pathway. These findings provide evidence that the biological properties of RET-MEN 2 mutants depend on the interplay between the RET isoforms and the nature of the activating MEN 2 mutation.
Insights
Germline mutations in the RET proto-oncogene cause endocrine neoplasias. This study reveals RET isoform and mutation type influence oncogenic activation and cellular differentiation, impacting disease development.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Germline mutations in the RET proto-oncogene are linked to multiple endocrine neoplasia types 2A and 2B (MEN 2A and MEN 2B) and familial medullary thyroid carcinoma (FMTC).
- These mutations lead to oncogenic activation of RET, a receptor tyrosine kinase.
- The distinct biological properties of different RET isoforms, particularly when altered by MEN 2 mutations, remain incompletely understood.
Purpose of the Study:
- To investigate the impact of specific MEN 2A (Cys634-->Arg) and MEN 2B (Met918-->Thr) mutations on two RET isoforms with differing carboxy-termini.
- To elucidate how these mutations and RET isoforms influence cellular transformation and neuronal differentiation.
- To explore the downstream signaling pathways involved in RET-mediated cellular changes.
Main Methods:
- Introduction of MEN 2A and MEN 2B mutations into two distinct RET isoforms (1114 and 1072 amino acids).
- Assessment of cellular transforming activity in fibroblasts.
- Evaluation of neuronal differentiation in pheochromocytoma PC12 cells, including neurite outgrowth.
- Analysis of Ras-dependent pathway involvement in RET-induced morphological changes.
Main Results:
- Both MEN 2A and MEN 2B mutations activated RET isoforms, leading to fibroblast transformation and PC12 cell neuronal differentiation.
- The long RET isoform with the MEN 2B mutation induced the most significant neurite outgrowth in PC12 cells.
- The short RET isoform with the MEN 2B mutation showed a markedly weaker differentiation effect.
- Constitutively activated RET oncoproteins induced morphological changes in PC12 cells via a Ras-dependent pathway.
Conclusions:
- The biological consequences of RET-MEN 2 mutations are dependent on the specific RET isoform involved.
- The nature of the activating MEN 2 mutation (MEN 2A vs. MEN 2B) significantly modulates the functional output of RET isoforms.
- These findings highlight the complex interplay between RET isoforms and mutation type in driving oncogenesis and cellular differentiation.