Anomalous p27kip1 expression in a subset of malignant gliomas

Regulation of p27 by ubiquitin ligases and its pathological significance in human lung carcinomas

Down-regulation of cyclin-dependent kinase inhibitor protein p27, due to enhanced degradation, is frequently observed in various cancers. The ubiquitin ligases that mediate this degradation have been identified as S-phase kinase-associated protein-2 (Skp2), Kip1 ubiquitylation-promoting complex (KPC), and p53-inducible protein with RING-H2 domain (Pirh2) as well. We investigated the correlation among expression of these 3 ligases and p27 status in surgical specimens of human lung carcinomas by immunohistochemical analysis. Among 93 cases, expressions of p27, Skp2, KPC, and Pirh2 were found in 89.2%, 59.1%, 59.1%, and 67.7%, respectively. Down-regulation of p27 in cancer cells was frequently observed in adenocarcinoma (AC) and squamous cell carcinoma (SCC), but not in small cell carcinoma (SmCC). Overexpression of ubiquitin ligases was variously observed among histological types: Skp2 was more frequently observed in SCC and SmCC, KPC in SCC and Pirh2 in AC, followed by SCC. Several novel findings were obtained: (i) cytoplasmic p27 was observed in 8.6%, most frequently in SCC (13.3%), and correlated with nodal metastasis (P=.0044), (ii) significant inverse correlation between nuclear p27 and Pirh2 expression was observed by statistical analysis and at the cellular level, and (iii) cytoplasmic Pirh2 and total (cytoplasmic and/or nuclear) Pirh2 were significantly correlated with the nodal status (P=.0225, 0.0314), the pathological stage (P=.0213, 0.0475) and recurrence-free survival (P=.0194, 0.0482, respectively) in AC. Altogether, our data suggests that p27 and its cognate ubiquitin ligases are specifically involved in the clinical profiles, and thus, molecular targeting of these ubiquitin ligases, in particular, Pirh2, may have therapeutic value for human lung carcinomas.

Combined loss of p21(waf1/cip1) and p27(kip1) enhances tumorigenesis in mice

The cell cycle inhibitors p21(Waf1/Cip1) and p27(Kip1) are frequently downregulated in many human cancers, and correlate with a worse prognosis. We show here that combined deficiency in p21 and p27 proteins in mice is linked to more aggressive spontaneous tumorigenesis, resulting in a decreased lifespan. The most common tumors developed in p21p27 double-null mice were endocrine, with a higher incidence of pituitary adenomas, pheochromocytomas and thyroid adenomas. The combined absence of p21 and p27 proteins delays the incidence of radiation-induced thymic lymphomas with a higher apoptotic rate, measured by active caspase-3 and cleaved PARP-1 immunoexpresion. These results provide experimental evidence for a cooperation of both cyclin-dependent kinase inhibitors in tumorigenesis in mice.

Expression of cell cycle inhibitors p21, p27, p14 and p16 in gliomas. Correlation with classic prognostic factors and patients' outcome

Gliomas are among the most aggressive and treatment-refractory of all human tumors. The aim of the present study is to evaluate the role of the expression of cell cycle molecules as prognostic indicators in gliomas. We immunohistochemically analyzed the expression of p21, p27, p14, p16, p53 and proliferation marker Ki67, in 67 low and high grade astrocytic tumors. High grade tumors exhibited higher labeling indices for Ki67 (P = 0.004), p53 (P = 0.039) and slightly higher index for p21 (P = 0.07) compared to low grade tumors. p14 and p16 were more frequently present in low grade tumors (P = 0.001 and P = 0.052, respectively). Worse survival was correlated with high grade tumors (P < 0.0001) and higher Ki67 index (P < 0.0001). Cox regression analysis revealed that only age, grade and marginally Ki67 index were independent prognostic factors. Cell cycle alterations are involved in the malignant progression of astrocytomas, but only age, tumor grade and proliferating index can predict the outcome of the patients with glioma.

Discovery of an oncogenic activity in p27Kip1 that causes stem cell expansion and a multiple tumor phenotype

The cell cycle inhibitor p27Kip1 also has cyclin-cyclin-dependent kinase (CDK)-independent functions. To investigate the significance of these functions in vivo, we generated a knock-in mouse in which four amino acid substitutions in the cdkn1b gene product prevent its interaction with cyclins and CDKs (p27CK-). In striking contrast to complete deletion of the cdkn1b gene, which causes spontaneous tumorigenesis only in the pituitary, the p27CK- protein dominantly caused hyperplastic lesions and tumors in multiple organs, including the lung, retina, pituitary, ovary, adrenals, spleen, and lymphomas. Moreover, the high incidence of spontaneous tumors in the lung and retina was associated with amplification of stem/progenitor cell populations. Therefore, independently of its role as a CDK inhibitor, p27Kip1 promoted stem cell expansion and functioned as a dominant oncogene in vivo. Thus, the p27CK- mouse unveils a dual role for p27 during tumorigenesis: It is a tumor suppressor by virtue of its cyclin-CDK regulatory function, and also an oncogene through a cyclin-CDK-independent function. This may explain why the cdkn1b gene is rarely inactivated in human tumors, and the p27CK- mouse in which the tumor suppressor function is lost but the cyclin-CDK-independent-oncogenic-function is maintained may represent a more faithful model for the widespread role of p27 misregulation in human cancers than the p27 null.

p27 and cyclin E/D2 associations in testicular germ cell tumors: implications for tumorigenesis

The cyclins are key regulators of cell cycle progression and cellular proliferation. We have previously shown that in testicular germ cell tumors, cyclin E expression correlates with more aggressive tumors, higher clinical stage, and the presence of pulmonary metastases. Here, we have examined the association between cyclin activation and the proliferative rate of the pluripotential testicular tumor cell. We have shown that in a panel of 30 testicular germ cell tumors, 15 cases (50%) expressed the cyclin dependent kinase inhibitor p27; of note, 13 of 14 embryonal carcinomas (93%) coexpressed cyclin E and p27, suggesting inhibition of this cyclin. We show that 25 of 30 (83%) of the testicular germ cell tumors express cyclin D2. Using immunoprecipitation assays from the embryonal carcinoma cell line NTera2 or from tumor cell extracts, we have shown that cyclin D2 is complexed with p27, consistent with its known ability to sequester and block the cyclin E inhibitory function of p27. From these results, we propose a model in testicular germ cell tumors, in particular embryonal carcinomas, whereby the overexpression of cyclin D2, a gene localized on chromosome 12p--a region of DNA amplification in germ cell tumors--leads to the functional sequestration of p27 in the presence of cyclin E and cyclin D2, thus favoring cellular proliferation.

Growth regulation by p27Kip1 is abrogated by multiple mechanisms in aggressive malignant lymphomas

The cyclin-dependent kinase inhibitor p27Kip1 is a key regulator of the G1/S transition, and an inverse relationship between p27Kip1 protein expression and proliferation index has been reported in malignant lymphomas. However, a subset of aggressive B-cell lymphomas demonstrates high p27Kip1 expression despite a high proliferation index. The aim of this study was to determine potential mechanisms by which lymphoma cells abrogate the growth inhibitory effect of high p27Kip1. The effect of transforming growth factor-beta (TGF-beta) and serum stimulation on p27Kip1 expression and cyclin E/cdk2 activity was investigated in four lymphoma cell lines, Jurkat, CEM-6, OCI-Ly1 and Nalm-6. Reactive lymphocytes responded to growth inhibitory TGF-beta by inducing p27Kip1 expression, with subsequent accumulation of cells in G0/G1. In contrast, TGF-beta did not alter the level of p27Kip1 in Jurkat, CEM-6 and OCI-Ly1 cells with no change in cyclin E/cdk2-kinase activity. Serum stimulation also did not result in a significant change in p27Kip1 expression. Western blot analysis of subcellular fractions demonstrated cytoplasmic p27Kip1, corroborated by immunocytochemistry in a subset of the lymphoma cells. Sequestration of p27Kip1 by cyclin D3 was observed in the nuclear and cytoplasmic fractions of Nalm-6, OCI-Ly-1 and NCEB cells. These results indicate that multiple mechanisms contribute to the abrogation of growth regulation by unscheduled high p27Kip1 protein expression including deficient response to TGF-beta and serum, sequestration by cyclin D3 and cytoplasmic displacement.

Expression of p27KIP1 in human gliomas: relationship between tumor grade, proliferation index, and patient survival

Numerous studies examining the prognostic significance of p27KIP1 expression in human cancer have shown that decreased expression often is an independent prognostic factor associated with worse survival. However, the prognostic value of p27KIP1 expression in gliomas is less well established. To further address this issue, we evaluated the relationship between p27KIP1 protein expression in a series of 50 astrocytomas with clinicopathologic parameters including age, tumor grade, MIB-1 proliferation index, and patient survival using both Western blot analysis and immunohistochemistry. The level of p27KIP1 protein expression in 9 nonneoplastic brain tissue specimens served as a control. Sixteen high-grade astrocytomas were analyzed by Western blot, and 26 high-grade astrocytomas were analyzed by immunohistochemistry for levels of p27KIP1 protein expression. Regardless of the technique used to measure p27KIP1, approximately 50% of the high-grade tumors were low expressors and the other 50% were high expressors. Thus, expression of p27KIP1 was independent of tumor grade. Loss of p27KIP1 expression is often associated with an increase in proliferative activity. We measured the rate of tumor cell proliferation using MIB-1 immunostaining in 16 high-grade astrocytomas to determine whether there was an inverse correlation between p27KIP1 expression and proliferation. No correlation between p27KIP1 expression and MIB-1 labeling index or patient survival was found. Using immunohistochemistry, we noted that the staining pattern of p27KIP1 in glioblastomas was mainly in the pseudopalisading cells that outline areas of necrosis. Because p27KIP1 can be up-regulated by hypoxia, this staining pattern would be consistent with our observation that hypoxia-inducible factor 1alpha is expressed primarily in pseudopalisading tumor cells around necrotic zones. It has been shown that a high level of p27KIP1 prevents apoptosis in hypoxic cells. Thus, maintenance of high levels of p27KIP1 in gliomas could result from the hypoxic microenvironment present within the tumor. No correlation was found between p27KIP1 expression and any of the clinicopathologic parameters tested, including patient age and tumor grade, the 2 strongest predictors of survival among glioma patients.

Inverse relationship between p27/Kip.1 and the F-box protein Skp2 in human astrocytic gliomas by immunohistochemistry and Western blot

The F-box protein Skp2 regulates G1-S transition by controlling p27/Kip.1. The deregulated expression of p27/Kip.1 plays a critical role in the pathogenesis of many human tumors. Its cellular levels depend on ubiquitin-mediated degradation. Recently, Skp2 has been demonstrated to mediate p27/Kip.1 degradation and to have oncogenic properties. In a series of astrocytic gliomas, immunohistochemistry and Western blot of p27/Kip.1 and Skp2 have been compared. p27/Kip.1 decreased with anaplasia and almost disappeared in glioblastomas (GBM), whereas Skp2 was absent or poorly expressed in well differentiated astrocytomas and it was diffusely or focally expressed in most GBM. Since the expression of Skp2 increases during G1-S transition, the correlation of Skp2 levels with malignancy might simply reflect the highest percentage of proliferating cells in anaplastic gliomas or alternatively be instrumental to p27/Kip.1 degradation.

Immunohistochemical markers for prognosis of oligodendroglial neoplasms

Despite numerous previous studies, oligodendrogliomas continue to generate considerable controversy in the identification of prognostic factors, including single histopathological patterns, and grade of tumor malignancy. The prognostic significance of various pathological and immunohistochemical factors has been intensively examined but numerous studies have yielded conflicting results. In the present study, biopsy samples of 123 oligodendrogliomas were examined immunohistochemically to evaluate a possible association between expression of various tumor-associated antigens and clinical outcome. Both the progression-free and overall survival times were significantly reduced for high-grade tumors, for Ki-S1 labeling index (LI) > 10%, for p27 LI < 20% and for p18, p53, and vascular endothelial growth factor (VEGF)-positive tumors. For low-grade tumors survival rates were significantly reduced for p27 LI less than 20%, whereas high-grade oligodendrogliomas with Ki-S1 LI greater than 10%, and with p18 positivity revealed significantly shortened survival times. We found no differences in survival times in patients with or without p 14ARF, p21, mdm2, and pRb immunoreactivity. Multivariate analysis revealed that risk of oligodendroglioma progression is associated with high-grade tumors, with Ki-S1 LI > 10%, and with p27 LI < 20%; whereas risk of death is associated with high-grade tumors, with Ki-S1 LI > 10%, and with p18 positivity. CART modeling process identified four final groups of oligodendroglioma patients: (1) thirty-nine patients with low-grade tumors and p27 LI > 20%; (2) twenty patients with low-grade tumors and p27 LI < 20%; (3) thirty-four patients with high-grade tumors and Ki-S1 LI < 10%; and (4) thirty patients with high-grade tumors and Ki-S1 LI >10%. In summary, both the p27 and Ki-S1 scores were found to be the strong predictors of oligodendroglioma outcome together with the WHO tumor grade and they seem to be useful for assessing individual prognosis in routinely processed specimens.

The prognostic significance of DNA topoisomerase II-alpha (Ki-S1), p21/Cip-1, and p27/Kip-1 protein immunoexpression in oligodendrogliomas

OBJECTIVE

To evaluate a possible association between clinical outcome of patients with oligodendroglioma and expression of 2 cyclin-dependent kinase inhibitors, p21/Cip-1 (p21) and p27/Kip-1 (p27), and of DNA topoisomerase II-alpha (Ki-S1), which has been recently used as a marker of cellular proliferation.

DESIGN

Ninety-one specially selected patients with cerebral oligodendrogliomas treated with surgery and radiotherapy were studied retrospectively. Tumor specimens were immunohistochemically examined with antibodies to p21, p27, and Ki-S1. A computerized color image analyzer was used to count immunostained nuclei.

RESULTS

The mean Ki-S1 labeling index (LI) was found to be significantly prominent for World Health Organization (WHO) high-grade tumors (9.5% vs. 3.2% for WHO low-grade tumors). In contrast, the mean p27 LI was significantly higher for low-grade tumors (43.3% vs 25.7% for high-grade tumors). The number of p21-positive cases and the mean p21 LI were found to be relatively equal for low- and high-grade tumors. For low-grade oligodendrogliomas, the progression-free and overall survival times were found to be significantly shorter for tumors with p27 LIs less than 20%. For high-grade oligodendrogliomas, survival times were significantly reduced for tumors with Ki-S1 LIs greater than 10%. Regression-tree analysis identified 4 groups of oligodendrogliomas with distinctly different outcomes: (1) 32 patients with low-grade tumors and p27 LIs greater than 20%; (2) 14 patients with low-grade tumors and p27 LIs less than 20%; (3) 25 patients with high-grade tumors and Ki-S1 LIs less than 10%; and (4) 20 patients with high-grade tumors and Ki-S1 LIs greater than 10%.

CONCLUSIONS

Immunoreactivity for Ki-S1 and p27 was found to be useful for further subdividing oligodendroglioma prognoses among low-grade and high-grade tumors. It seems unlikely that p21 immunohistochemistry will be of value for determining clinical outcomes for patients with oligodendrogliomas.

Neurofibromatosis type 1-associated unusual pleomorphic astrocytoma displaying continual malignant progression

Patients with neurofibromatosis type 1 (NF1) often have gliomas as a complication, most of which are benign pilocytic astrocytomas which have arisen in optic pathways. In the present case, a 17-year-old girl (at death) with stigmata of NF1, initially had a bulky tumor mass in the left thalamus, developing into the lateral ventricle, at 13 years of age. Partially resected tissue samples showed pleomorphic astrocytoma with abundant xanthoma cells and degenerative structures such as Rosenthal fibers (RF) and eosinophilic granular bodies. Fine eosinophilic granules identical to RF, both immunophenotypically and ultrastructurally, were also seen. The residual tumor was subtotally resected 6 months later, and the tumor histology was essentially similar as before, accompanying the regenerative structures; this was believed to be a good prognostic indicator. However, several anaplastic features such as mitosis, necrosis and vascular proliferation appeared even in areas rich in the regenerative structures. After a 2-year, disease-free interval, multiple tumor relapse occurred in June 1997. Partially resected tumor tissues were composed of monotonous small anaplastic cells with prominent proliferative activity. Surprisingly, the tumor cells had retained eosinophilic granules within the cell bodies. Postoperative chemotherapy with procarbazine, MCNU and vincristine (PCV) suppressed the residual tumor dramatically, but the regrowing tumor finally became uncontrollable, leading to the patient's death. TP53 mutation was not detected, while p27 immunopositivity was constantly high during malignant progression, suggesting acquisition of proliferative activity to overcome p53 and p27 inhibitory functions. A review of previously published reports failed to reveal any cases of this type.