The impact of p53 tumor suppressor gene on glioma biology

MicroRNA-145 is downregulated in glial tumors and regulates glioma cell migration by targeting connective tissue growth factor

Glioblastomas (GBM), the most common and aggressive type of malignant glioma, are characterized by increased invasion into the surrounding brain tissues. Despite intensive therapeutic strategies, the median survival of GBM patients has remained dismal over the last decades. In this study we examined the expression of miR-145 in glial tumors and its function in glioma cells. Using TCGA analysis and real-time PCR we found that the expression of miR-145/143 cluster was downregulated in astrocytic tumors compared to normal brain specimens and in glioma cells and glioma stem cells (GSCs) compared to normal astrocytes and neural stem cells. Moreover, the low expression of both miR-145 and miR-143 in GBM was correlated with poor patient prognosis. Transfection of glioma cells with miR-145 mimic or transduction with a lentivirus vector expressing pre-miR 145 significantly decreased the migration and invasion of glioma cells. We identified connective tissue growth factor (CTGF) as a novel target of miR-145 in glioma cells; transfection of the cells with this miRNA decreased the expression of CTGF as determined by Western blot analysis and the expression of its 3′-UTR fused to luciferase. Overexpression of a CTGF plasmid lacking the 3′-UTR and administration of recombinant CTGF protein abrogated the inhibitory effect of miR-145 on glioma cell migration. Similarly, we found that silencing of CTGF decreased the migration of glioma cells. CTGF silencing also decreased the expression of SPARC, phospho-FAK and FAK and overexpression of SPARC abrogated the inhibitory effect of CTGF silencing on cell migration. These results demonstrate that miR-145 is downregulated in glial tumors and its low expression in GBM predicts poor patient prognosis. In addition miR-145 regulates glioma cell migration by targeting CTGF which downregulates SPARC expression. Therefore, miR-145 is an attractive therapeutic target for anti-invasive treatment of astrocytic tumors.

[Astrocytic neoplasms and correlation with mutate p53 and Ki-67 proteins]

The astrocytic neoplasms respond by 60% of the central nervous system tumors, being the study of the molecular biology an important step for the understanding of the genesis and biological behavior of these diseases. The Ki-67 proteins, which are markers of the cellular proliferation, and p53, which is the product of the tumor suppressor gene TP53, are both important tumoral markers. This study intends to identify and quantify the Ki-67 and p53 proteins in astrocytic tumors of different grades of malignancy, as well as to analyze their relations with age and gender. Ki-67 and p53 proteins in 47 patients with surgically resected astrocytic neoplasms were studied through immunohistochemistry. They have been previously classified and reviewed concerning their histological grade, as suggested by the World Health Organization. The immunomarked cellular nuclei were quantified by the program Imagelab-softium for the absolute parametric reason between the nuclei of the positive cells and the total amount of tumoral cells, being counted 1000 cells. The lineation used has been transversal not controlled. For the statistical analysis the variables were divided into groups. For the Ki-67 they were absent, <5% and >5% and for p53 they were absent (0), <25% (1+), between 25 and 50% (2+), between 50 and 75% (3+), and higher than 75% (4+). Ki-67 was present in 37 cases (78.72%) evidencing a correlation with a higher malignancy degree (p<0,001). p53 was present in 14 cases (35.13%) with a higher correlation with astrocytoma grade IV (p=0.59). There has not been a statistically significant correlation between p53 and Ki-67, as well as among these variables, age and gender. The hypotheses of a greater presence of Ki-67 and p53 in astrocytic neoplasms with a higher degree of malignancy, except for the correlation between grade III and p53, is corroborated by the results of this study.

P53 and MIB-1 immunohistochemistry as predictors of the clinical behavior of nonfunctioning pituitary adenomas

BACKGROUND

P53 expression and increased MIB-1 proliferation index have been shown to correlate with invasive behavior in pituitary adenomas. The purpose of this study was to determine whether these indices could be used to predict a higher likelihood of recurrence in clinically nonfunctional pituitary adenomas and thus guide adjuvant therapy.

METHODS

Fifty-one clinically nonfunctional pituitary adenomas were selected from the database at the Vancouver Hospital and Health Sciences Center between the years 1990-1998. Included were 32 nonrecurrent and 19 recurrent adenomas.

RESULTS

The mean initial labelling index for p53 in nonrecurrent tumours was 0.38% (0-1.58%), while it was 0.46% (0-3.65%) for recurrent adenomas. The mean initial MIB-1 index for nonrecurrent tumours was 1.63% (0.08-9.36%), while for recurrent tumours it was 1.92% (0-7.76%). The percentage of p53 positive adenomas was 66% for nonrecurrent tumours and 68% for recurrent tumours. None of the differences in the labelling indices between the recurrent and nonrecurrent groups was statistically significant. As 12 patients (38%) in the nonrecurrent group had undergone radiotherapy as initial adjuvant therapy after surgery and none of the recurrent group had done so, patients who did not receive radiotherapy in the nonrecurrent group were analyzed separately. Again, none of the differences in the labelling indices between the recurrent and nonrecurrent groups was statistically significant when the effect of radiotherapy was removed from the analysis.

CONCLUSIONS

The results demonstrate no statistical difference in the p53 or MIB-1 labelling indices between recurrent and nonrecurrent nonfunctional pituitary adenomas. Concern should be raised in attaching too much clinical significance to these labelling indices, especially with respect to p53 as a predictor of the clinical behavior of nonfunctional pituitary adenomas.