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RET cooperates with RB/p53 inactivation in a somatic multi-step model for murine thyroid cancer
A B Coxon1, J M Ward, J Geradts
1Department of Genetics, National Cancer Institute and National Naval Medical Center, Bethesda, Maryland 20889, USA.
Abstract:
Mice bred to carry germline Rb and p53 null alleles are associated with a tumor spectrum that overlaps with the inherited multiple endocrine neoplasia-1 (MEN1) and MEN2 syndromes in humans, including medullary thyroid cancer (MTC). To study the genetic basis for these tumors, we microdissected MTC specimens or obtained fresh MTC tissue from nine independent Rb(+/-) p53(+/-) mice, amplified the region of the Ret gene known to be mutated in human MTC, and detected acquired missense Ret mutations in four different mice. These mutations were localized to a group of tandem cysteines which are analogous to activating germline mutations observed in human MEN2A and familial MTC (FMTC). To determine whether the remaining wild type Rb allele was inactivated in these murine MTC samples, we subjected tumor tissue to immunohistochemical staining with an Rb antibody, and demonstrated the absence of RB staining in murine MTC, while normal tissue retained RB nuclear staining. These findings demonstrate the ability of the gene knockout model to recapitulate somatic multi-step tumorigenesis and suggest that the development of a murine neuroendocrine tumor requires mutational dysregulation within both receptor tyrosine kinase and nuclear tumor suppressor gene pathways.
Insights
Mice with Rb and p53 gene defects developed tumors similar to human endocrine neoplasia syndromes. Researchers found acquired Ret mutations and Rb inactivation, suggesting multi-step tumor development in these mice.
Area of Science:
- Oncology
- Genetics
- Endocrinology
Background:
- Germline Rb and p53 null alleles in mice mimic human multiple endocrine neoplasia (MEN) syndromes.
- These mouse models develop tumors, including medullary thyroid cancer (MTC), similar to MEN1 and MEN2.
Purpose of the Study:
- To investigate the genetic basis of MTC in Rb(+/-) p53(+/-) mice.
- To understand the role of Ret mutations and Rb inactivation in multi-step tumorigenesis.
Main Methods:
- Microdissection and genetic analysis of MTC specimens from nine Rb(+/-) p53(+/-) mice.
- Amplification of the Ret gene region and detection of acquired mutations.
- Immunohistochemical staining for Rb protein in tumor and normal tissues.
Main Results:
- Acquired missense Ret mutations were identified in four of the nine mice.
- These Ret mutations occurred in cysteine residues analogous to human MEN2A/FMTC mutations.
- Absence of nuclear Rb staining was observed in all murine MTC samples, indicating Rb inactivation.
Conclusions:
- The Rb/p53 knockout mouse model effectively recapitulates somatic multi-step tumorigenesis.
- Murine neuroendocrine tumor development requires dysregulation in both receptor tyrosine kinase (Ret) and nuclear tumor suppressor (Rb) pathways.