P18 is a tumor suppressor gene involved in human medullary thyroid carcinoma and pheochromocytoma development

Abstract

In multiple endocrine neoplasia syndrome Type 2 (MEN2), medullary thyroid carcinoma (MTC) and pheochromocytoma (PC) are associated with hereditary activating germ-line mutations in the RET proto-oncogene. Also in a large percentage of sporadic MTCs and PCs, somatic RET mutations appear to be involved in tumor formation. In one single MEN2 family an extensive variety in disease expression may be observed, indicating that additional genetic events are responsible for progression of the disease towards a more aggressive phenotype. However, these additional mutations in both hereditary and sporadic MTC and PC development are largely unknown. Here, we show for the first time the presence of somatic mutations in the cell cycle regulator P18 in human RET-associated MTCs and PCs. Each of these mutations causes an amino acid substitution in the cyclin dependent kinaseinteracting region of P18 INK4C . Since these mutations partly inhibited P18 INK4C function and reduced its stability, our findings implicate P18 as a tumor suppressor gene involved in human MTC and PC development. ' 2008 Wiley-Liss, Inc.Key words: P18 INK4C; medullary thyroid carcinoma; RET; tumor suppressor gene; multistep tumorigenesis Multiple endocrine neoplasia Type 2 (MEN2) is an autosomal dominantly inherited cancer syndrome. The clinical expression of MEN2 varies, although all patients develop medullary thyroid carcinoma (MTC) or its precursor C-cell hyperplasia (CCH). MEN2 can be subdivided in MEN2A, MEN2B and familial MTC (FMTC). MEN2A is characterized by MTC, pheochromocytoma (PC), and hyperparathyroidism. MEN2B is characterized by MTC, PC and mucosal ganglioneuromas (in the colon, lips and tongue). FMTC patients solely develop MTC. MTC originates from the calcitonin producing neuroendocrine C-cells in the thyroid gland, and PC originates from the neuroendocrine chromaffin cells in the adrenal medulla. 1 MEN2 patients carry an activating germ-line mutation in the RET proto-oncogene, leading to constitutive activation of its encoded transmembrane receptor tyrosine kinase RET. The MEN2 phenotype correlates strongly with specific RET mutations. 2,3 In MEN2A the mutations affect cysteine residues in the extracellular domain of the protein. The most commonly affected Cysteine is C634. 4,5 In MEN2B, the most common mutation (in 95% of the cases) results in a Methionine to Threonine substitution at position 918 in the intracellular domain of the protein. [6][7][8] Somatic RET mutations have been detected in 23-69% of sporadic MTC, the vast majority of which has the M918T mutation, as well as in 10-15% of sporadic PC, with M918T in 50% of the cases. 9 Carriers of the same germ-line RET mutation, both related and unrelated, can develop MTC and PC at widely varying ages, suggesting that in addition to the mutated RET gene, other oncogenic events are required for the development of these tumors. The most frequently detected chromosomal alteration in MTC and PC is loss of a specific part or of the entire short arm of chromosome 1. [10][11][12] The most comm...

Polymorphisms of cell cycle control genes influence the development of sporadic medullary thyroid carcinoma

“…A frequent finding in MTC tumors is the loss of heterozygosity at chromosome 1p, indicating a potential tumor suppressor gene in this locus (4). Homozygous deletion of the CDKN2C gene was also observed in the human MTC cell line (TT) bearing a RET mutation (16). These data indicate that the CDKN2C gene may act as a tumor suppressor and may facilitate MTC development (4).…”

“…Nine polymorphisms were genotyped: CDKN1A (rs1801270 and rs1059234), CDKN1B (rs2066827 and rs34330), CDKN2A (rs11515), CDKN2B (rs2069426, rs3731239, and rs1063192), and CDKN2C (rs12885) using the TaqMan system (Applied Biosystems), as described previously (17). These SNPs were chosen because they have previously been associated with thyroid carcinoma or other tumor risks as described in Table 1 (13,15,16,20,21,22).…”

“…There have been some reports associating polymorphisms of cell cycle genes with s-MTC (13,14,15,16). The CDKN1B V109G polymorphism was reported to influence the clinical course of patients presenting sporadic MTC (15).…”

2813 Comprehensive genomic profiling of clinically advanced medullary thyroid carcinoma

“…Future clinical studies need to address whether CCND1 or CDK4 amplification may associate with sensitivity to CDK4/6 inhibitors, as preliminary clinical data suggest for other tumor types [34,35]. CDKN2C has previously been observed to be inactivated in MTC and CDKN2C loss cooperated with oncogenic RET to promote MTC development in mice [36,37]. Alterations in cell cycle genes co-existent with RET mutations may therefore contribute to resistance to RET targeting.…”

Suppressed protein expression of the death-associated protein kinase enhances 5-fluorouracil-sensitivity but not etoposide-sensitivity in human endometrial adenocarcinoma cells

“…3, only p18 mRNA was significantly suppressed by DAPK knockdown. Although p18, a member of cyclindependent kinase inhibitor, is reported to be a tumor suppressor gene (19)(20)(21), further investigations are needed to clarify whether suppressed p18 expression can affect anticancer drug sensitivity of the cells. …”