Cell death in retinoblastoma: electron microscopic, immunohistochemical, and DNA fragmentation studies

A Study of Gene Expression of Survivin, its Antiapoptotic Variants, and Targeting Survivin In Vitro for Therapy in Retinoblastoma

Apoptosis is a natural process regulated by apoptotic and antiapoptotic molecules. We investigated mRNA expression of survivin and its splice variants, along with B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X (Bax), in a cohort of 20 retinoblastoma (RB) tumors by real-time polymerase chain reaction. We hypothesized a correlation between the Bcl-2/Bax and survivin splice variants and also that expression of these would be associated with clinicopathologic features of tumors. The Bcl-2 expression was significantly higher (P<0.001) in RB, and Bcl-2/Bax ratio was remarkably higher in poorly differentiated tumors. A statistically significant higher expression of Survivin-WT (wild type) compared with its variant Survivin-2β (P<0.05) was observed. Bcl-2 did not exhibit positive correlation with any of the survivin variants except Survivin-2β, whereas Bax exhibited significant (P<0.05) correlation with the variants. Thus, it could be suggested that a superior player out of a likely interaction between the variants and Bcl-2/Bax uses its activity for the progression of RB. Silencing of Survivin-WT in the Y79 cell line was studied by siRNA technology and cell-permeable dominant negative survivin (SurR9-C84A). siRNA showed higher proapoptotic effects and increased caspase 3/7 activity in Y79 cells. Effective internalization of SurR9-C84A in Y79 cells induced cytotoxic effects. Thus, the current study confirms survivin as a promising target for therapy.

Immunohistochemistry of apoptosis-related proteins in retinoblastoma

Retinoblastoma is the most common intraocular malignant neoplasia during childhood and results from the partial or total inactivity of the retinoblastoma protein (pRb). In the absence of pRb, the E2F transcription factors increase the levels of cell cycle proteins as well as some pro-apoptotic proteins. We intended to study the immunohistochemistry profile of apoptotic-related proteins in retinoblastoma. We also evaluated the association between the expression of apoptotic protein and stage of tumor or survivor after a 5year follow up. Apoptosis-related proteins (Apaf-1, Bak, Bax, Bcl-2, Bcl-xL, Bim-long, MDM2, p53, pro-caspase-3, PUMA, Smac/DIABLO and cleaved caspase-3) were evaluated using immunohistochemistry on tissue microarrays which contained samples of retinoblastoma tumors taken from ninety-three patients without any treatment previous to surgery. The immunohistochemistry reactions were evaluated using an optical microscope as well as the ACIS III^® platform. The pro-apoptotic proteins (APAF-1, Bax, p53, PUMA, Smac/DIABLO) were more frequently expressed than the anti-apoptotic proteins (Bcl-2, Bcl-xL and MDM2). The protein Bcl-xL had a negative correlation with cleaved caspase-3, a marker of cell apoptosis. Bcl-xL may be implicated in an apoptosis block.

The apoptotic paradox in retinoblastoma

The purpose of this study was to investigate the clinicopathological features and the expression of proteins involved in cell proliferation and the different pathways of apoptosis in retinoblastoma. Nineteen retinoblastoma patients were included, and mitotic index (MI) and apoptotic index (AI) were assessed. The expression of MIB-1, p53, caspase-3, Bcl-2, and Fas protein was assessed by immunohistochemistry. Mann-Whitney U test and Fisher's exact test were used for statistical comparison. High MI (mean 16.84, range 0-66) and high MIB-1 expression (mean 57.89, range 0-90) were found. The MI was significantly related to MIB-1 expression (P= 0.01). The tumors showed a high apoptotic index (mean 40.26, range 1-110), and the AI was associated with the mitotic index (P= 0.02). The caspase-3 expression was positively related to the AI (P= 0.03), although a small number of tumors with no significant or very low caspase-3 staining showed a high number of apoptotic cells, suggestive of a caspase-3-independent apoptosis pathway. Bcl-2 expression was not significantly related to AI (P= 0.07). No striking relationship was found in expression patterns of p53, Bcl-2, caspase-3, and Fas. In conclusion, we found that (1) cell proliferation and apoptosis are linked in retinoblastoma; (2) activation of effector caspase-3 induces apoptosis in retinoblastoma, but Bcl-2 overexpression does not prevent apoptosis in many tumors; (3) there is a p53-independent pathway in approximately one-quarter of cases; (4) the findings suggesting a caspase-3-independent pathway might lead to apoptosis in retinoblastoma; and, finally, we found no consistent pattern of expression of apoptotic and antiapoptotic molecules, suggesting that in retinoblastoma there is no preference for any single pathway of apoptosis. Confirmation of the results in a large set of tumors would be useful.

Quantitative analysis of apoptosis in retinoblastoma

PURPOSE

The rate of apoptosis in retinoblastoma (Rb) and the factors that may influence this rate, such as therapy prior to surgery, amount of necrosis in tumour tissue, differentiation and laterality of the tumour, were investigated.

METHODS

Thirty-one specimens (25 enucleation, six exenteration) with Rb were studied. Prior to final surgery, three patients received systemic chemotherapy, one intravitreal chemotherapy, one transpupillary thermotherapy, one external beam radiotherapy and one high-dose oral methylprednisolone therapy. The apoptotic index (AI,%) was calculated by counting at least 1000 cells under light microscopy (x 100) using TUNEL (terminal deoxynu-cleotidyl transferase-mediated dUTP nick-end labelling) method.

RESULTS

The mean AI was 2.75 plus minus 1.2. No statistically significant association was observed between rate of apoptosis and the presurgical treatment, extent of necrosis, tumour differentiation and laterality.

CONCLUSION

Apoptosis is an important mechanism of cell death, and may be a limiting factor for tumour progression. In this study, the rate of apoptosis was not affected by any of the studied parameters.