Clinicopathological and molecular features of sessile serrated adenomas with dysplasia or carcinoma.

OBJECTIVE: Sessile serrated adenomas (SSAs) are the precursors of at least 15% of colorectal carcinomas, but their biology is incompletely understood. We performed a clinicopathological and molecular analysis of a large number of the rarely observed SSAs with dysplasia/carcinoma to better define their features and the pathways by which they progress to carcinoma. DESIGN: A cross-sectional analysis of 137 SSAs containing regions of dysplasia/carcinoma prospectively collected at a community GI pathology practice was conducted. Samples were examined for BRAF and KRAS mutations, the CpG island methylator phenotype (CIMP) and immunostained for MLH1, p53, p16, ß-catenin and 0-6-methylguanine DNA methyltransferase (MGMT). RESULTS: The median polyp size was 9 mm and 86.5% were proximal. Most were BRAF mutated (92.7%) and 94.0% showed CIMP. Mismatch repair deficiency, evidenced by loss of MLH1 (74.5%) is associated with older age (76.7 versus 71.0; p<0.0029), female gender (70% versus 36%; p<0.0008), proximal location (91% versus 72%; p<0.02), CIMP (98% versus 80%; p<0.02) and lack of aberrant p53 (7% versus 34%; p<0.001) when compared with the mismatch repair-proficient cases. Loss of p16 (43.1%) and gain of nuclear ß-catenin (55.5%) were common in areas of dysplasia/cancer, irrespective of mismatch repair status. CONCLUSIONS: SSAs containing dysplasia/carcinoma are predominantly small (<10 mm) and proximal. The mismatch repair status separates these lesions into distinct clinicopathological subgroups, although WNT activation and p16 silencing are common to both. Cases with dysplasia occur at a similar age to cases with carcinoma. This, together with the rarity of these 'caught in the act' lesions, suggests a rapid transition to malignancy following a long dwell time as an SSA without dysplasia.

Increased expression of senescence markers p14(ARF) and p16(INK4a) in breast cancer is associated with an increased risk of disease recurrence and poor survival outcome.

AIMS: Breast cancer is a hormonally driven disease. Cellular senescence is an age-related irreversible cell cycle arrest at the G1 phase upon induction. The aim of this study was to characterize the expression patterns of the senescence markers p14(ARF) , p16(INK4a) and p21(WAF1/Cip1) during breast cancer progression in a large patient cohort. METHODS AND RESULTS: We conducted a retrospective study of 1080 patients with invasive ductal carcinoma, no special type, over an 11-year period. We performed immunohistochemical staining on tissue microarrays that included normal, benign hyperplasia, ductal carcinoma in situ and invasive ductal carcinoma tissue from each patient. Invasive ductal carcinomas showed higher expression of p14(ARF) and p16(INK4a) but lower expression of p21(WAF1/Cip1) than non-malignant tissues. There were significant correlations of normal, benign, preinvasive and malignant tissues with p14(ARF) , p16(INK4a) and p21(WAF1/Cip1) expression (P < 0.05). Univariate comparison showed a correlation between high p16(INK4a) expression and poor survival (P = 0.000) and an increased risk of relapse (P = 0.000), whereas high p14(ARF) expression correlated only with an increased risk of relapse (P = 0.038). Multivariate analysis showed p16(INK4a) to be an important prognostic factor for overall survival (P = 0.011) and disease-free survival (P = 0.004), with p14(ARF) also being a significant prognostic factor for disease-free survival (P = 0.043). Moreover, patients showing both high p16(INK4a) expression and and high p14(ARF) expression had an adjusted three-fold increased risk of disease recurrence (P < 0.05) and a two-fold increased risk of all-cause-related death (P < 0.05). CONCLUSIONS: These finding suggest p16(INK4a) expression and p14(ARF) expression may play an important role in the progression of proliferative breast tissue to invasive cancer, and may be useful as prognostic factors.

The processed isoform of the translation termination factor eRF3 localizes to the nucleus to interact with the ARF tumor suppressor.

The eukaryotic releasing factor eRF3 is a multifunctional protein that plays pivotal roles in translation termination as well as the initiation of mRNA decay. eRF3 also functions in the regulation of apoptosis; eRF3 is cleaved at Ala73 by an as yet unidentified protease into processed isoform of eRF3 (p-eRF3), which interacts with the inhibitors of apoptosis proteins (IAPs). The binding of p-eRF3 with IAPs leads to the release of active caspases from IAPs, which promotes apoptosis. Although full-length eRF3 is localized exclusively in the cytoplasm, p-eRF3 localizes in the nucleus as well as the cytoplasm. We here focused on the role of p-eRF3 in the nucleus. We identified leptomycin-sensitive nuclear export signal (NES) at amino acid residues 61-71 immediately upstream of the cleavage site Ala73. Thus, the proteolytic cleavage of eRF3 into p-eRF3 leads to release an amino-terminal fragment containing NES to allow the relocalization of eRF3 into the nucleus. Consistent with this, p-eRF3 more strongly interacted with the nuclear ARF tumor suppressor than full-length eRF3. These results suggest that while p-eRF3 interacts with IAPs to promote apoptosis in the cytoplasm, p-eRF3 also has some roles in regulating cell death in the nucleus.

Different Expression of p16INK4a and p14ARF in cervical and lung cancers.

AIM: This study aimed to assess clinical significance of expression of p16INK4a and p14ARF proteins in cervical and lung cancers. MATERIALS AND METHODS: Expression of these proteins was examined in 50 cervical cancer specimens (42 hr-HPV-associated cervical cancer and 8 non-hr-HPV-associated cervical cancer) and 127 lung cancer specimens (34 squamous cell carcinomas, 33 adenocarcinomas, 36 bronchioloalveolar carcinomas, and 24 small cell lung cancers) by immunohistochemistry. RESULTS: Overexpression of both p16INK4a and p14ARF was found in 100% cervical cancer specimens and in, respectively, 61.42% and 30.79% of lung cancer specimens. Thus, expression ratio of p16INK4a and p14ARF was significantly higher in cervical cancer than in lung cancer (p < 0.01). Both proteins were unexpressed in 38 lung cancer specimens (29.92%), and there was no correlation between the expressions of these proteins. CONCLUSIONS: Different patterns of p16INK4a and p14ARF expression in cervical and lung cancer patients suggest different involvement of these proteins in the development of either cancer type. We propose p16INK4a and p14ARF as biomarkers in clinical assessment for cervical cancer.

Molecular analysis of the Ink4a/Rb1-Arf/Tp53 pathways in radon-induced rat lung tumors.

Inhalation of radon is closely associated with an increased risk of lung cancers. While the involvement of Ink4a in lung tumor development has been widely described, the tumor suppressor gene has not been studied in radon-induced lung tumors. In this study, loss of heterozygosity (LOH) analysis of the Cdkn2a locus, common to the Ink4a and Arf genes, was performed on 33 radon-induced rat lung tumors and showed a DNA loss in 50% of cases. The analysis of p16(Ink4a) protein expression by immunohistochemistry revealed that 50% of the tumors were negative for this protein. Looking for the origin of this lack of expression, we observed a low frequency of homozygous deletion (6%), a lack of mutation, an absence of correlation between promoter methylation and Ink4a mRNA expression and no correlation between LOH and protein expression. However, a tendency for an inverse correlation between p16(Ink4a) and pRb protein expression was observed. The expressions of p19Arf, Mmd2 and Mdm4 were not deregulated and only 14% of the tumors were mutated for Tp53. These results indicated that Ink4a/Cdk4/Rb1 pathway deregulation, more than Arf/Mdm2/Tp53 pathway, has a major role in the development of these tumors through p16(Ink4a) deregulation. However, all known mechanisms of inactivation of the pathway do not play a recurrent role in these tumors and the actual origin of the lack of p16(Ink4a) protein expression remains to be established.

Expression of p16 in oral cancer and premalignant lesions.

BACKGROUND: Expression of p16 has been proposed as a marker for malignant transformation. This study aimed to evaluate p16 expression in oral squamous cell carcinoma (OSCC) and premalignant lesions including oral leukoplakia (OL) with and without dysplasia. METHODS: Expression of p16 was investigated in 56 samples including OSCC, OL with and without dysplasia, and normal oral mucosa. Expression of p16 was identified by immunohistochemistry, using the CINtecTM p16INK4a Histology Kit. Both nuclear and/or cytoplasmic staining of the keratinocytes were considered to be positive and the percentage of positive cells was calculated. RESULTS: Expression of p16 was detected in 3/16 (18.75%) cases of OSCC, in 4/15 (26.7%) cases of OL without dysplasia, and in none of OL with dysplasia and normal mucosa. No significant differences in p16 expression prevalence were found among OSCC, OL with and without dysplasia and normal mucosa. The percentages of positive cells in OSCC and OL without dysplasia were 0.89 and 0.17, respectively. No significant difference in the percentage of positive keratinocytes was found. CONCLUSION: As a marker, p16 is not reliable for oral mucosal dysplasia and malignant transformation.

Molecular markers in the surgical margin of oral carcinomas.

BACKGROUND: Local or regional lymph node recurrence is the most common pattern of treatment failure in oral squamous cell carcinoma (SCC). The local recurrence rate is 30% even when the surgical resection margin is diagnosed as tumour free. Accumulation of genetic changes in histologically normal epithelium in the surgical resection margin may explain the local recurrence rate. The purpose of this study is to investigate the presence of senescence markers, which may represent early malignant changes in the margin that in routine pathological evaluations are classified as histologically normal. METHODS: Formalin-fixed, paraffin-embedded surgical specimens from 16 consecutive patients with oral SCC and a clear surgical margin were obtained. The margin was analysed by immunohistochemistry for p53, p16, Chk2, Laminin-5 and glycosylated oncofetal fibronectin. RESULTS: Two patterns of p53 expression were found in the histologically normal epithelium in the surgical resection margin. One was characterized by no protein expression in the majority of cells, except for small clusters of basal and parabasal cells with nuclear staining. The other was characterized by p53 expression in the nuclei of most basal cells. The expression of p16 was confined to small groups of cells in the basal cell layer whereas Chk2 was only seen in one case. Upregulation of the stromal proteins, Laminin-5 or glycosylated oncofetal fibronectin, was only seen at regions of invasion. CONCLUSION: Small groups of cells expressing p53 and p16 were found in the surgical resection margin that appeared to be histologically normal and may represent early malignant changes.

The determination of stage in nonmuscle urothelial carcinoma: Staining pattern of caspase-8.

CONTEXT: Urothelial carcinoma (UC) is one of the most frequent epithelial tumors worldwide. AIMS: We aimed to investigate the protein expressions of caspase-8, p53, murine double minute 2 (mdm2), and p14ARF in nonmuscle UCs and to correlate the findings with clinicopathological characteristics. SETTINGS AND DESIGN:: A total of 50 patients who had pTa and pT1 tumors were analyzed. SUBJECTS AND METHODS: The protein expressions of caspase-8, p53, mdm2, and p14ARF were analyzed by immunohistochemistry. STATISTICAL ANALYSIS USED: Chi-square test was done using SPSS version 16.0 (SPSS, Inc., Chicago, IL, USA). RESULTS: Cytoplasmic caspase-8 expression was significantly higher in pT1 UCs while nuclear caspase-8 expression was significantly higher in pTa UCs (P = 0.005 and P = 0.011, respectively). Cytoplasmic caspase-8 expression was also higher in high-grade UCs (P = 0.035). The expression of p53, mdm2, and p14ARF was not also related with pathological stage or grade (P > 0.05 for all). The p14ARF expression was related with nuclear caspase-8 expression in most of the patients. Complete agreement among nonmuscle UCs for immunohistochemical expression of p14 and nuclear caspase-8 was seen in 41 cases, and the pairwise kappa agreement value was substantial (κ =0.614). The patients who had recurrence were positive for both p53 and mdm2 or either p53 or mdm2 (P = 0.025). CONCLUSIONS: These results suggested that the staining pattern of caspase-8 might be helpful for determining of the stages in nonmuscle UC. It was also showed that the expression status of p53 and mdm2 were related with the recurrence.

Assessment of health status by molecular measures in adults ranging from middle-aged to old: Ready for clinical use?

In addition to measures already used in clinical practice, molecular measures have been proposed to assess health status, but these have not yet been introduced into clinical practice. We aimed to test the association of functional capacity measures used in current practice and molecular measures with age and health status. The cohort consisted of 178 middle-aged to old participants of the Leiden Longevity Study (range 42-82years). We tested associations between functional capacity measures (physical tests: grip strength, 4-meter walk, chair stand test; cognitive tests: Stroop test, digit symbol substitution test and 15-picture learning test) with age and with cardiovascular or metabolic disease as a measure of the health status. These associations with age and health status were also tested for molecular measures (C reactive protein (CRP), numbers of senescent p16INK4a positive cells in the epidermis and dermis and putative immunosenescence (presence of CD57+ T cells)). All functional capacity measures were associated with age. CRP and epidermal p16INK4a positivity were also associated with age, but with smaller estimates. Grip strength and the Stroop test were associated with cardiovascular or metabolic disease, as was epidermal p16INK4a positivity. All associations with cardiovascular or metabolic disease attenuated when adjusting for age. In conclusion, in middle-aged to old persons, the molecular measures tested here were more weakly associated with age and health status than functional capacity measures. Whether these molecular measures associate more closely with health status in the elderly or in specific groups of patients needs to be explored further.

ARF Confers a Context-Dependent Response to Chemotherapy in Muscle-Invasive Bladder Cancer.

Muscle-invasive bladder cancer (MIBC) generally responds poorly to treatment and tends to exhibit significant mortality. Here we show that expression of the tumor suppressor p14ARF (ARF) is upregulated in aggressive subtypes of MIBC. Accumulation of ARF in the nucleolus is associated with poor outcome and attenuated response to chemotherapy. In both genetically engineered mouse models and murine xenograft models of human MIBC, we demonstrate that tumors expressing ARF failed to respond to treatment with the platinum-based chemotherapy agent cisplatin. Resistance was mediated in part by the integrin-binding protein ITGB3BP (CENPR) and reflected ARF-dependent impairment of protein translation, which was exaggerated by drug treatment. Overall, our results highlight a context-dependent role for ARF in modulating the drug response of bladder cancer. Cancer Res; 77(4); 1035-46. ©2017 AACR.

Wild-type p53 overexpression and its correlation with MDM2 and p14ARF alterations: an alternative pathway to non-small-cell lung cancer.

PURPOSE: We found a relatively reduced frequency of p53 mutation with a much greater frequency of p53 protein overexpression, which reflected stabilization of p53 protein in the absence of p53 gene mutation. Therefore, we investigated the possibility of alternative mechanisms leading to p53 protein stabilization. PATIENTS AND METHODS: We performed gene and protein alteration studies on p53 and its upstream effectors, MDM2 and p14ARF, in tumors from 94 non-small-cell lung cancer (NSCLC) patients. RESULTS: Immunohistochemical and sequencing analyses indicated that 37 tumors showed overexpression of wild-type p53. An absence of nuclear staining of MDM2 protein was found in 95% of these tumors (35 of 37; P < .001). The tumors with negative MDM2 staining showed a significantly high concordance of loss of Akt activity and low MDM2 mRNA expression (P < .001). Sequencing analysis revealed five distinct MDM2 splicing variants disrupting the conserved p53 binding domain. Corresponding variant proteins were detected in three lung cancer cell lines using the Western blot analysis. Our results also indicated that among the tumors with overexpression of the wild-type p53, 92% (34 of 37) showed immunoreactivity to p14ARF (P = .001). In addition, the deregulation of p53 and MDM2 genes was significantly associated with squamous lung cancer (P < .05) and was correlated with advanced stages (P < .05) and poor prognosis (P < .05). CONCLUSION: Our data suggest that immunopositivity of p14ARF together with a low expression of MDM2 contributes to accumulation of the wild-type p53, and that deregulation of the p53-MDM2-p14ARF pathway is important in the pathogenesis and outcome of a subset of NSCLC.

Frequent p16 CpG island hypermethylation in primary remnant gastric cancer suggesting an independent carcinogenic pathway.

Cancer found in the post-operative remnant stomach includes both newly developed cancer after surgery for benign-disease (PRC) and metachronous multiple cancer (MRC). Differences in the carcinogenic pathway between PRC and MRC have been suspected from clinical studies. However, no study has demonstrated the difference in molecular alteration between these diseases. P16 is inactivated predominantly by epigenetic change, rather than genetic alteration. We analyzed the methylation status and protein expression of the p16 gene in cancers of the remnant stomach. Eleven lesions of PRC, 24 lesions of MRC and corresponding non-cancerous tissue, as well as 13 primary gastric cancer (PC) lesions were examined. DNA was extracted by the micro-dissection method from paraffin-embedded surgical specimens. The methylation status of the promoter CpG island of the p16 gene was examined by using a methylation-specific polymerase chain reaction technique. To detect protein expression, immunohistochemical staining was employed. p16 promoter hypermethylation was observed more often in remnant gastric cancer than in PC. A significantly more frequent hypermethylation in the p16 gene was found in PRC (64%) than in MRC (21%) or PC (23%). Moreover, a significant correlation was found between p16 promoter hypermethylation and diminishment of protein expression in cancers of the remnant stomach. Silencing of the p16 gene by methylation of its promoter CpG island was suggested as a unique molecular mechanism in the carcinogenesis of PRC compared with MRC or PC.

Expression of TAp73 and DeltaNp73 isoform transcripts in thyroid tumours.

AIM: This study was aimed to determine p73 status in thyroid tumours. METHODS: Differential expression of the TAp73, DeltaTAp73 transcripts was measured in a panel of 60 thyroid malignancies by quantitative RT-PCR. RESULTS: By comparison to normal thyroid tissue surrounding the tumours, we observed significant downregulation of TP73 transcripts in adenomas and in differentiated carcinomas. Correlations were found in normal tissue specimens between the expression of TAp73 and DeltaNp73 transcripts and that of p53, p14ARF p16INK4a, but these correlations were lost in carcinomas (PTC or FTC). CONCLUSIONS: We have found significant variations of TAp73, DeltaNp73, p53, p14ARF p16INK4a, expressions and correlations between the expressions of those different genes in thyroid cancer.

P16 loss and mitotic activity predict poor survival in patients with peritoneal malignant mesothelioma.

PURPOSE: Peritoneal malignant mesothelioma is an aggressive neoplasm for which intensive therapy improves survival in a subset of patients. We hypothesized that pathologic variables would stratify patients into favorable and unfavorable survival subgroups. EXPERIMENTAL DESIGN: Fifty-four patients with peritoneal malignant mesothelioma were evaluated for trimodal therapy from 1995 to 2003. Two pathologists evaluated pathologic variables independently, and p16 status was analyzed by immunohistochemistry. RESULTS: Patients not receiving trimodal therapy had a significantly increased risk of death [hazard ratio (HR), 9.6; 4.3-21.6; P < 0.0001]. Biphasic histology was also associated with increased risk of death (HR, 8.5; 3.4-21.8; P < 0.0001). In multivariate analysis adjusting for treatment modality and histologic type, high mitotic rate and p16 loss were associated with increased risk of death (HR, 3.074; 1.05-9.0; P < 0.04 and HR, 3.65; 1.3-10.2; P < 0.014, respectively). CONCLUSIONS: Biphasic histology, increased mitotic rate, and p16 loss were independently associated with poorer survival in peritoneal malignant mesothelioma. Among the trimodal treated patients, increased mitotic rate was associated with increased risk of death.

p14ARF is a component of the p53 response following ionizing irradiation of normal human fibroblasts.

Ionizing radiation leads to rapid stabilization and activation of the p53 tumor suppressor. Previous reports demonstrate that murine p19ARF cooperates with p53 in the cellular response to gamma irradiation. Here, we show that endogenous ARF sequentially interacts with p53 and MDM2 following irradiation of primary human and mouse embryonic fibroblasts. Shortly after irradiation, p14ARF binds p53 independently of MDM2. As nuclear pools of p53 decline, endogenous p14ARF co-immunoprecipitates with MDM2 and is localized within the nucleolus. Interestingly, p14ARF nucleolar localization during this response is abrogated in cells lacking functional p53. Taken together, our data suggest that human and murine ARF contribute to the mammalian DNA damage response.

Human p14(Arf): an exquisite sensor of morphological changes and of short-lived perturbations in cell cycle and in nucleolar function.

The human Ink4a/Arf tumor suppressor locus encodes two distinct products: p16(Ink4a) which prevents phosphorylation and inactivation of the retinoblastoma protein and, p14(Arf), a nucleolar protein which activates the function of the tumor suppressor p53 protein in the nucleoplasm in response to oncogenic stimulation through an as yet ill-defined mechanism. Here we show that the level of endogenous p14(Arf) and its balance between the nucleolus and the nucleoplasm in HeLa cells are exquisitely sensitive to changes in cell morphology and to short-lived perturbations in cell cycle and in nucleolar function such as those induced by the cyclin-dependent kinase inhibitor, roscovitine, and the casein kinase II and RNA synthesis inhibitor, DRB. Most remarkably, whereas p14(Arf) predominantly concentrates in the nucleolus of interphase cells and transiently disappears between metaphase and early G1 under normal growth conditions, it massively and reversibly accumulates in the nucleoplasm of postmitotic and S-phase cells upon short-term treatment with roscovitine and, at a lesser extent, DRB. In line with the fact that the nuclear level of p53 reaches a peak between mid-G1 and the G1/S border in p53-expressor cells which lack Arf expression, these results provide a clue that, in p53+/Arf+ cells, Arf proteins might serve both to speed and to amplify p53-mediated responses in conditions and cell cycle periods in which the mechanisms involved in p53 stabilization and activation are not fully operational. They further suggest that human endogenous p14(Arf) might activate p53 pathways in physiologic situations by acting inside the nucleoplasm, especially when normal cell cycle progression and nucleolar function are compromised.

Expression of the p14ARF tumor suppressor predicts survival in acute myeloid leukemia.

Cell cycle aberrations are associated with therapy outcome in many types of cancer. We analyzed mRNA expression levels of 18 cell cycle-related genes in bone marrow samples from 78 acute myeloid leukemia (AML) patients and six controls using high-throughput quantitative RT-PCR. Samples of AML patients contained significantly increased mRNA expression levels of the mdm2 and c-myc oncogenes. Also, the average expression levels of p14ARF and p16INK4A were higher in patient samples compared to controls. Leukemic blasts and control bone marrow samples did not differ significantly in the expression levels of proliferation-associated genes such as cyclin A2 and pcna. When single genes were analyzed for prognostic significance in Kaplan-Meier and Cox regression analyses, a low p14ARF level emerged as a strong and independent predictor for poor survival (P=0.04 and 0.029). Subsequently, p14ARF mRNA levels were analyzed in a second, independent patient population (n=57). Again, low p14ARF levels were associated with a worse outcome. Finally, immunohistochemistry analysis of AML tissue arrays confirmed the widespread expression of c-myc and p14ARF in AML on the protein level. Taken together, the expression of the p53 regulators mdm2 and p14ARF are altered in AML, and low p14ARF levels indicate a poor prognosis.

Studies on expression of p14ARF and MDM2 in human thyroid neoplasms.

AIM: We sought to evaluate the expression and clinical significance of p14ARF and MDM2 proteins in thyroid neoplasm. METHODS: Immunohistochemical streptavidin-peroxidase (S-P) method was used to detect the expression of p14ARF and MDM2 proteins in 78 cases of papillary thyroid carcinoma (PTC), 34 cases of papillary thyroid microcarcinoma (PTMC) and 45 cases of thyroid adenoma. RESULTS: The expression of p14ARF and MDM2 protein differed significantly (P<0.01) among three group. The positivity rate of p14ARF protein in PTC was significantly lower than that in thyroid adenoma (P=0.002) and PTMC (P=0.008). While the positivity rate of MDM2 protein in PTC was significantly higher than that in thyroid adenoma (P=0.000) and PTMC (P=0.009). There was a significant correlation found between the expressions of p14ARF and MDM2 proteins in PTC (P=0.013) and PTMC (P=0.012). Also, a significant correlation was found between p14ARF protein expression and lymph node metastasis in PTC (P=0.011). CONCLUSION: It was concluded that p14ARF and MDM2 proteins might be involved in the induction and development of PTC and PTMC whereas p14ARF also had diagnostic value in determining the biological behavior of PTC.

p14ARF induces the relocation of HDM2 and p53 to extranucleolar sites that are targeted by PML bodies and proteasomes.

BACKGROUND: p14ARF is a protein product of the alternative reading frame of the human INK4a locus. It functions as a tumor suppressor protein. p14ARF suppresses growth through p53-dependent and p53-independent pathways. RESULTS: p14ARF protein localizes primarily to the nucleoli. Here we show that in transfected cells p14ARF also appears in Hsp70 positive extranucleolar inclusions. The formation of p14ARF inclusions induces the parallel re-localization p53 and HDM2 to these sites that are also targeted by PML bodies and proteasomes. CONCLUSION: Our data show that co-localization between p53, HDM2 and p14ARF occurs at extranucleolar sites. Accumulation of PML and proteasomes at these sites suggest that the components of the nuclear inclusions are targeted for proteasome-mediated degradation.

A melanoma-predisposing germline CDKN2A mutation with functional significance for both p16 and p14ARF.

The CDKN2A locus on human chromosome 9p21 encodes two proteins, p16 and p14ARF, that mainly regulate cell cycle progression and cell survival via the pRb and p53 pathways, respectively. Germline mutations in CDKN2A have been linked to development of cutaneous melanoma in some families with hereditary melanoma. Due to overlapping open reading frames in exon 2, some mutations in this exon affect both p16 and p14ARF. We previously reported a 24bp deletion in CDKN2A exon 2 in a patient with multiple primary melanomas and melanoma heredity. To further clarify the possible role of the 24bp deletion for melanoma development, especially with respect to p14ARF, we have studied the cellular distribution and function of the resulting p14ARF del (77-84) and p16 del (62-69) mutant proteins. We found that p14ARF del (77-84) had decreased nucleolar localization, and was less efficient than wt p14ARF in stabilizing p53, inducing G1 cell cycle arrest, and inhibiting colony formation. The p16 del (62-69) mutant localized predominantly to the cytoplasm, did not induce G1 cell cycle arrest, and failed to suppress colony formation. We conclude that p14ARF del (77-84) has retained the ability to stabilize MDM2 and p53, but that it is less potent than wt p14ARF. This partial functional defect may complement the clearly defective p16 del (62-69) mutant and thus contribute to melanoma development in patients carrying the 24bp deletion in CDKN2A.