Immunohistochemical analysis of p53 and p21 in human primary glioblastomas in relation to proliferative potential and apoptosis

Immunoexpression of tumor suppressor genes p53, p21 WAF1/CIP1 and p27 KIP1 in humam astrocystic tumors

The aim of the present study was to evaluate the tumor suppressor genes p53, p21 WAF1/CIP1 and p27 KIP1 expression in astrocytic tumors, correlating the findings with the histopathological grade (WHO). An immunohistochemical study of the p53, p21 and p27 proteins using the streptavidin-biotin-peroxidase method was performed in fifty-five astrocytomas (13 grade I, 14 grade II, 7 grade III and 21 grade IV) and five samples of non-tumor brain tissue (negative control). p53 positive indices (PI) and labeling indices (LI) showed tendency to increase according to malignant progression. The nuclear expression of p27 presented similar inclination, except for the PI reduction verified in grade IV tumors. Otherwise, the cytoplasmic p27 staining was more evident between high-grade tumors (III and IV). p53 and nuclear p27 expression was correlated with the histological classification (p<0.01; test H). On the other hand, p21 indices revealed a propensity to reduction in agreement with malignant evolution of the astrocytic tumors, except for high scores observed in grade IV tumors. The non-tumor samples did not show any expression of these proteins. These results indicated the p53 mutation as an initial, relevant and potentially predictor of tumor progression event in astrocytomas, with the detection of p21 protein as an important resource for the deduction of functional situation of this gene. Moreover, the activation of p27 KIP1 was preserved in the astrocytic tumors and its cytoplasmic manifestation seems to be resultant of its nuclear expression, not demonstrating a direct impact in astrocytomas tumorigenesis.

Correlation analysis between the expression of P21WAF1/CIP1, P16 proteins and human glioma

AIM

Glioma is the most common neoplasm of the brain. Unfortunately, surgical cure of it is practically impossible and clinical course is primarily determined by the biological behaviour of the tumour cells. The purpose of this study was to investigate the correlation between the expression levels of P21WAF1/CIP1, P16 proteins and the grading of glioma.

METHODS

T98G human glioma cell line, normal human astrocyte (HA) cell line, tumour tissue samples from 70 patients suffering from glioma and normal brain tissues from 20 cases with brain contusion were investigated. The expression levels of P21WAF1/CIP1 and P16 proteins were detected using SABC immunohistochemical staining and semi-quantitive reverse transcriptase polymerase chain reaction (RT-PCR) assay. Then, the correlation of the two markers' expression with glioma grading of patients was analysed.

RESULTS

The expression levels of P21WAF1/CIP1 and P16 proteins in the T98G cell line were much lower than that in the HA cell line. Their positive expression rates in glioma tissues were 55.71% and 42.86% respectively, and a significant increase was observed in normal brain tissues (p = 0.012, 0.008). Combined with the result of semi-quantitive RT-PCR, we could demonstrate that the expression intensity of P21WAF1/CIP1 and P16 decreased with the glioma grade increase. Co-expression of them was also found in glioma and normal brain tissues. Furthermore, there was a negative correlation between the two markers' expression and glioma grading of patients (rs = -0.68, -0.56).

CONCLUSIONS

The positive expression rate and co-expression rate of P21WAF1/CIP1 and P16 proteins could reflect the malignant grade of glioma to some extent, and they can be considered as a sensitive index for glioma grading.

Relationship between apoptosis and proliferation in secondary tumors of the brain

A correlation between apoptosis and proliferation in astrocytomas and oligodendrogliomas, but not in glioblastomas, has been previously reported. An index for apoptosis and proliferation was established for each tumor in a series of 20 brain metastases, and its correlation was studied using the Spearman rank correlation test. Apoptosis index (AI) ranged between 1 and 78% (mean SD: 11.48+/-16.4). Proliferation index (PI) ranged between 2.4 and 21% (mean+/-SD: 8.23+/-4.8). When the relationship between AI and PI was studied, a clear correlation was found (r: 0.8965, 95% CI: 0.74-0.95; P < 0.0001). Therefore, it is concluded that a clear correlation exists between proliferation and apoptosis in secondary tumors of the brain.

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.

Immunohistochemical markers for prognosis of ependymal neoplasms

Intracranial ependymomas are the third most common primary brain tumor in children. Although clinical and histological criteria for ependymoma prognosis are recognized, studies have reported contradictory results. Prognostic significance based on immunohistochemistry of ependymomas has been reported in a few studies. One-hundred and twelve patients with intracranial ependymomas were examined retrospectively for immunoexpression of various tumor-associated antigens and apoptosis. The results demonstrated significant preponderance of expression of the tenascin, vascular endothelial growth factor protein (VEGF), epidermal growth factor (EGFR) and p53 protein in high-grade tumors. Also high-grade ependymomas revealed more prominent labeling indices (LI) for proliferative marker Ki-S1 and apoptotic index (AI), and lower LI for cyclin-dependent kinase inhibitors p27/Kipl and pl4ARF. For low-grade ependymomas the progression-free survival time (PFS) was found to be significantly shorter for Ki-S1 LI > 5%, and for tenascin, VEGF and EGFR positivity. For high-grade ependymomas PFS was found to be significantly reduced for p27 LI < 20%, p14ARF LI < 10%, for p53 positivity, and for AI < 1%. The CART modeling process exhibited five final groups of ependymoma patients (1) low-grade and tenascin-negative; (2) low-grade and tenascin-positive; (3) high-grade and p53-negative with p14 LI > 0%; (4) high-grade with combination of either p53 positivity and p14 LI > 10% or p53 negativity and p14 LI < 10%; (5) high-grade and p53-positive with pl4 LI < 10%. In summary, some immunohistochemical variables were found to be the strong predictors of ependymoma recurrence and they seem to be useful for assessing individual tumor prognosis in routinely processed biopsy specimens together with tumor grade. For histologically benign ependymomas immunohistochemical study should be focused on Ki-S1, tenascin, EGFR and VEGF evaluation, whereas p53 expression and number of p27, p14 and ISEL-positive nuclei will be of value in determining PFS from high-grade ependymomas.

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.

Expression of p57(KIP2) potently blocks the growth of human astrocytomas and induces cell senescence

Astrocytic tumors frequently exhibit defects in the expression or activity of proteins that control cell-cycle progression. Inhibition of kinase activity associated with cyclin/cyclin-dependent kinase co-complexes by cyclin-dependent kinase inhibitors is an important mechanism by which the effects of growth signals are down-regulated. We undertook the present study to determine the role of p57(KIP2) (p57) in human astrocytomas. We demonstrate here that whereas p57 is expressed in fetal brain tissue, specimens of astrocytomas of varying grade and permanent astrocytoma cell lines do not express p57, and do not contain mutations of the p57 gene by multiplex-heteroduplex analysis. However, the inducible expression of p57 in three well-characterized human astrocytoma cell lines (U343 MG-A, U87 MG, and U373 MG) using the tetracycline repressor system leads to a potent proliferative block in G(1) as determined by growth curve and flow cytometric analyses. After the induction of p57, retinoblastoma protein, p107, and E2F-1 levels diminish, and retinoblastoma protein is shifted to a hypophosphorylated form. Morphologically, p57-induced astrocytoma cells became large and flat with an expanded cytoplasm. The inducible expression of p57 leads to the accumulation of senescence-associated beta-galactosidase marker within all astrocytoma cell lines such that approximately 75% of cells were positive at 1 week after induction. Induction of p57 in U373 astrocytoma cells generated a small population of cells ( approximately 15%) that were nonviable, contained discrete nuclear fragments on Hoechst 33258 staining, and demonstrated ultrastructural features characteristic of apoptosis. Examination of bax and poly-(ADP ribose) polymerase levels showed no change in bax, but decreased expression of poly-(ADP ribose) polymerase after p57 induction in all astrocytoma cell lines. These data demonstrate that the proliferative block imposed by p57 on human astrocytoma cells results in changes in the expression of a number of cell cycle regulatory factors, cell morphology, and a strong stimulus to cell senescence.