Evidence of ubiquitous in vivo and in vitro expression of pro-apoptotic Smac/DIABLO protein in meningioma cell lines

Although meningiomas are one of the most common tumors in the central nervous system, the adjuvant treatment for recurrent or malignant meningiomas is not satisfactory. An intense interest in evaluating new molecular markers that may serve as potential therapeutic targets exists. Changes in apoptosis mechanisms play important roles in tumor pathogenesis. One pro-apoptotic protein is Smac/DIABLO, which neutralizes the inhibitors of apoptosis (IAPs). As Smac/DIABLO has not been previously analyzed in meningiomas, We investigated the expression of Smac/DIABLO and survivin in primary meningioma cultures in vivo and in vitro. Expression of Smac/DIABLO, survivin and single-stranded (ss)DNA in vivo were determined immunohistochemically in 100 meningioma surgical specimens, dura and normal human cortex. The expression of the apoptotic enzymes in vitro was analyzed after RNA and protein isolation of all meningiomas via Western blotting and PCR. All examined meningiomas and normal cerebral cortex displayed intense positive cytoplasmic Smac/DIABLO immunoreactivity. Survivin and ssDNA were expressed in all surgical specimens and showed weak staining overall. Examination of Smac/DIABLO protein via Western blotting showed distinct signals in the cytoplasmic extracts. PCR analysis displayed no changes of Smac/DIABLO and survivin expression in different meningioma grades, normal human cortical cortex or dura. Constant high-level Smac/DIABLO respectively low-level survivin expression in meningiomas and normal brain demonstrate similar apoptotic behavior of meningiomas compared to normal brain tissue. These findings indicate no pathological overexpression of survivin in meningiomas as is evident in several other cancer types impeding apoptosis.