Cyclin D1 is a target molecule transcriptionally activated by aberrant β-catenin in Wnt signalling, while prolyl isomerase Pin1 promotes cyclin D1 overexpression directly or through accumulation of β-catenin in cancer cells. This study aimed to elucidate whether Pin1 was involved in cyclin D1 overexpression and aberrant β-catenin in thyroid tumourigenesis by examining 14 follicular adenomas (FAa) and 14 papillary thyroid carcinomas (PTCs). All PTCs displayed cyclin D1 overexpression and strong cytoplasmic β-catenin and/or decreased membrane β-catenin expression by immunohistochemistry. Overexpression of cyclin D1 mRNA was observed in 45.5% of FAs and 54.5% of PTCs by TaqMan real-time PCR. Pin1 expression was observed in PTC by immunostaining and was confirmed by reverse transcriptase-PCR. There was a strong correlation between cyclin D1 and Pin1/cytoplasmic/membrane β-catenin expression (p < 0.001), and between Pin1 and cytoplasmic (p < 0.001)/membrane (p = 0.002) β-catenin expression in thyroid tumours. Mutation of the β-catenin gene could not be detected in PTC. Western blot analysis demonstrated high levels of cyclin D1 and β-catenin as well as Pin1 expression in a human PTC cell line possessing wild-type β-catenin and APC genes. This study suggests that both cyclin D1 overexpression and aberrant β-catenin expression are of significance in thyroid tumours. Pin1 expression appears to correlate closely with the level of cyclin D1 and aberrant β-catenin expression in thyroid tumours such as FA and PTC. Pin1 may be an important factor in regulating cyclin D1 and β-catenin expression during thyroid carcinogenesis.

Defective DNA damage response (DDR) can result in genomic instability (GIN) and lead to the transformation into cancer. P53-binding protein 1 (53BP1) belongs to a family of evolutionarily conserved DDR proteins. Because 53BP1 molecules localize at the sites of DNA double strand breaks (DSBs) and rapidly form nuclear foci, the presence of 53BP1 foci can be considered as a cytologic marker for endogenous DSBs reflecting GIN. Although it has been proposed that GIN has a crucial role in the progression of thyroid neoplasms, the significance of GIN during thyroid tumorigenesis remains unclear, particularly in patients. We analyzed, therefore, the level of GIN, as detected with immunofluorescence of 53BP1, in 40 cases of resected thyroid tissues. This study demonstrated a number of nuclear 53BP1 foci in thyroid cancers, suggesting a constitutive activation of DDR in thyroid cancer cells. Because follicular adenoma also showed a few 53BP1 nuclear foci, GIN might be induced at a precancerous stage of thyroid tumorigenesis. Furthermore, high-grade thyroid cancers prominently exhibited an intense and heterogeneous nuclear staining of 53BP1 immunoreactivity, which was also observed in radiation-associated cancers and in mouse colonic crypts as a delayed response to a high dose ionizing radiation, suggesting increased GIN with progression of cancer. Thus, the present study demonstrated a difference in the staining pattern of 53BP1 during thyroid carcinogenesis. We propose that immunofluorescence analysis of 53BP1 expression can be a useful tool to estimate the level of GIN and, simultaneously, the malignant potency of human thyroid tumors. ' 2007 Wiley-Liss, Inc.Key words: thyroid cancer; genomic instability; 53BP1; ATM; immunofluorescence DNA damage response (DDR) genes, such as p53, are frequently mutated in human cancer. Defective DDR responses can thus result in genomic instability (GIN) and lead to the transformation of normal cells into cancer cells. Thyroid cancer has been shown to display aneuploidy, one form of GIN. 1 It has been proposed that GIN has a crucial role in the progression of thyroid neoplasms. 2 Thus, transfection of mutant HRAS V12 or mutant BRAF V600E induced GIN in a rat thyroid cell line, manifesting as loss of chromosomal material, mitotic bridge formation and misaligned chromosomes. 3-5 Recently, we found RET oncogene amplification in human thyroid cancers. 6 Oncogene amplification is common in solid tumors and correlates with a poor prognosis for patients with ovarian cancer (HER-2/neu), breast cancer (C-MYC, HER-2/neu), neuroblastoma (N-MYC), or small cell lung cancer (C-MYC). [7][8][9][10] In thyroid cancers, RET amplification correlated with radiation-induced and high-grade malignancy, providing further evidence for the involvement of GIN in tumor progression. 6 P53-binding protein 1 (53BP1) belongs to a family of evolutionarily conserved DDR proteins with C-terminal BRCT domains. 11,12 The ataxia-teleangiactasis mutated (ATM) DDR kinase is well known as a sensor molecule for DNA damage. Both...

Cyclin D1 overexpression and correlation with aberrant beta-catenin expression were demonstrated in PMC. Cyclin D1 expression was significantly associated with tumour size and LN metastases in PMC. Cyclin D1 may be up-regulated at an early stage of thyroid carcinogenesis and promote tumour growth and metastatic potency in PMC through activation of the Wnt/beta-catenin pathway.

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Epidermal cells are the first cells to be exposed to environmental genotoxic agents such as ultraviolet and ionizing radiations, which induce DNA double strand breaks (DSB) and activate DNA damage response (DDR) to maintain genomic integrity. Defective DDR can result in genomic instability (GIN) which is considered to be a central aspect of any carcinogenic process. P53-binding protein 1 (53BP1) belongs to a family of evolutionarily conserved DDR proteins. Because 53BP1 molecules localize at the sites of DSB and rapidly form nuclear foci, the presence of 53BP1 nuclear foci can be considered as a cytological marker for endogenous DSB reflecting GIN. The levels of GIN were analyzed by immunofluorescence studies of 53BP1 in 56 skin tumors that included 20 seborrheic keratosis, eight actinic keratosis, nine Bowen's disease, nine squamous cell carcinoma, and 10 basal cell carcinoma. This study demonstrated a number of nuclear 53BP1 foci in human skin tumorigenesis, suggesting a constitutive activation of DDR in skin cancer cells. Because actinic keratosis showed a high DDR type of 53BP1 immunoreactivity, GIN seems to be induced at the precancerous stage. Furthermore, invasive cancers exhibited a high level of intense, abnormal 53BP1 nuclear staining with nuclear accumulation of p53, suggesting a disruption of DDR leading to a high level of GIN in cancer cells. The results of this study suggest that GIN has a crucial role in the progression of skin carcinogenesis. The detection of 53BP1 expression by immunofluorescence can be a useful histological marker to estimate the malignant potential of human skin tumors. (Cancer Sci 2008; 99: 946-951) T he skin is the primary barrier for humans against the external environment. Therefore, epidermal cells are the first cells to be exposed to physical and chemical genotoxic agents such as UV and IR. IR effectively induces DSB in normal cells and activates DDR pathways to maintain genomic integrity. DDR genes, such as p35, are frequently mutated in human cancer. Thus, defective DDR can result in GIN which is generally considered to be a central aspect of any carcinogenic process. (1,2) It has been shown that gamma irradiation induced skin tumors in mice. Most of the tumor-bearing mice showed a loss of the wild-type p53 allele. Since no skin tumor was found in wild-type p53 mice, this suggested a requirement of p53 loss in irradiation-induced skin carcinogenesis. (3) The incidence of skin cancer was reported to be elevated in atomic bomb survivors, which also suggested a radiation etiology in human skin carcinogenesis. (4) 53BP1 belongs to a family of evolutionarily conserved DDR proteins with C-terminal BRCT (BRCA1 C-terminus) domains. (5,6) The 53BP1 is a nuclear protein that rapidly localizes at the sites of DSB, and cooperatively activates p53 with other kinases. (7-12) Subsequently, activated p53 plays a critical role in cellular responses to genomic injury, such as cell cycle arrest, DNA repair, and apoptosis. (13,14) It has been well documented in vitro with immunofluorescen...

BACKGROUND: Radiation etiology is suggested in the occurrence of basal cell carcinoma (BCC) of the skin among atomic bomb (A‐bomb) survivors. Any genotoxicity, including ionizing radiation, can induce a DNA damage response (DDR), leading to genomic instability (GIN), which allows the accumulation of mutations during tumorigenesis. In this study, the authors evaluated the presence of GIN in the epidermis of survivors as a late effect of A‐bomb radiation. METHODS: In total, 146 BCCs, including 23 cases arising from nonexposed skin, were identified in survivors from 1968 to 1999. The incidence rate (IR) of BCC was calculated with stratification by distance in kilometers from the hypocenter (≤1.5 km, 1.6‐2.9 km, and ≥3 km). Nineteen epidermal samples surrounding BCC at the nonexposed sites were collected and tested for p53 binding protein 1 (53BP1) expression with immunofluorescence. 53BP1 rapidly forms nuclear foci at the sites of DNA double strand breaks (DSBs). Because 1 manifestation of GIN is the induction of endogenous DSBs, the level of 53BP1‐focus formation (DDR type) can be considered as a marker for GIN. RESULTS: The incidence rate of BCC increased significantly as exposure distance approached the hypocenter. Of the 7 epidermal samples from the proximal group (≤1.5 km), 5 samples predominantly expressed DDR and an abnormal type of 53BP1 expression. In contrast, 4 of 5 samples from the distal group (≥3 km) and all samples from the control group predominantly expressed the stable type of 53BP1 expression in the epidermis. CONCLUSIONS: The current results demonstrated the endogenous activation of DDR in the epidermis surrounding BCC in the proximal group, suggesting the presence of a GIN in the survivors as a late effect of A‐bomb radiation, which may indicate a predisposition to cancer. Cancer 2009. © 2009 American Cancer Society.

Abnormal/high DDR type of 53BP1 expression might be associated with GIN and papillary/trabecular morphology at an early stage of PTC carcinogenesis through BRAF(V) (600E) mutation.

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