The cohesin-interacting protein, precocious dissociation of sisters 5A/sister chromatid cohesion protein 112, is up-regulated in human astrocytic tumors.

Glioblastoma multiforme (GBM) is the most prevalent, highly malignant, invasive and difficult-to-treat primary brain tumor in adults. At the genetic level, it is characterized by a high degree of chromosomal instability and aneuploidy. It has been shown that defects in the mitotic spindle checkpoint could lead to the development of aneuploidy as well as tumorigenesis. Additional proteins regulating sister chromatid cohesion could also be involved in maintaining the fidelity of chromosome segregation. One such protein is the precocious dissociation of sisters 5A (Pds5A), also known as sister chromatid cohesion protein 112. It is a nuclear protein, expressed from the S right through to the mitotic phase. It is highly conserved from yeast to man and plays a role in the establishment, maintenance and dissolution of sister chromatid cohesion. The mutation of Pds5A orthologs in lower organisms results in chromosome missegregation, aneuploidy and DNA repair defects. It is considered that such defects can cause either cell death or contribute to the development of cancer cells. Indeed, altered expression levels of Pds5A have been observed in tumors of the breast, kidney, oesophagus, stomach, liver and colon. Malignant gliomas, however, have not been analysed so far. Herein, we report on the cloning of Rattus norvegicus Pds5A and on the analysis of its expression pattern in rat tissue. We also show that Pds5A is significantly overexpressed at both the mRNA and protein level and that this overexpression correlates positively with the WHO grade of human gliomas. However, functional assays show that the siRNA-mediated knockdown of Pds5A affects sister chromatid cohesion but does not influence mitotic checkpoint function or the proliferation and survival of GBM cells. Although the mechanism by which Pds5A functions in GBM cells remains unclear, its overexpression in high grade gliomas implies that it could play a pivotal role during the development and progression of astrocytic tumors.

RAF expression in human astrocytic tumors.

RAF proteins are well known oncoproteins. The B-RAF has been shown to be activated by mutations in a multitude of human cancers. Alterations of C-RAF expression are discussed to play a role in lung cancer. Only for A-RAF no link to tumorigenesis has been published so far. Malignant gliomas are the most prevalent primary brain tumors of adults. They are highly invasive and very difficult to treat, despite of surgery, gamma-irradiation and chemotherapy. Although a role of the mitogenic Ras-RAF-MEK-ERK signalling cascade in brain tumor development is well established, there are only few reports available addressing alterations in RAF sequence or protein expression and function in human gliomas. We analysed the mutational status of A-RAF and B-RAF in human glioblastomas (GBM) by sequencing. Then we checked for RAF gene amplification by dot blot hybridization and examined RAF mRNA and protein expression patterns in human astrocytic gliomas of WHO grade II (LGA) and IV (GBM) by semiquantitative RT-PCR and Western blotting, respectively. The results were correlated with patients prognosis. Finally, we performed functional assays to address a putative function of A-RAF in glioma cell proliferation and migration. We showed that RAF mutations are a rare event in glioblastoma multiforme. A-raf gene amplification was more often detected and overexpression of all three RAF proteins on mRNA and protein level was regularly found in human malignant gliomas. Whereas A-RAF and C-RAF expression was negatively correlated with the patients prognosis, B-RAF expression had a positive effect. Since neither A-RAF, nor C-RAF expression had any influence on proliferation and migration of GBM cells, putative functions of C-RAF in angiogenesis and of A-RAF in regulation of metabolism are discussed. Our data indicate that RAF proteins might be valuable targets for small molecule therapies. However, initially specific functions of RAF during tumorigenesis have to be elucidated.

Expression analysis of the autosomal recessive primary microcephaly genes MCPH1 (microcephalin) and MCPH5 (ASPM, abnormal spindle-like, microcephaly associated) in human malignant gliomas.

Patients with autosomal recessive primary microcephaly have a small but architecturally normal brain containing a reduced number of neurons. Microcephalin and ASPM are two of the genes causing this disease. Both are centrosomal proteins involved in cell cycle regulation. Whereas microcephalin is a component of the DNA damage response and a repressor of telomerase function, ASPM is required for the proper formation of a central mitotic spindle and ensures symmetric, proliferative divisions of neuro-epithelial cells. Both proteins are also involved in the regulation of tumor growth. Microcephalin expression is reduced in breast cancer cell lines and human tumors of the ovary and prostate. Reduction in microcephalin mRNA expression correlates with increased chromosomal instability. ASPM mRNA is overexpressed in transformed human cell lines and tumors, and its increased expression is positively associated with proliferation of glioblastoma cells. Glioblastomas are the most prevalent malignant brain tumors in adults, characterized by increased invasiveness, an aggressive local growth pattern and short survival periods of patients. In this study, we analysed the expression of microcephalin mRNA and ASPM mRNA and protein in a panel of 15 glioblastomas and 15 astrocytoma WHO grade II by semi-quantitative RT-PCR, Western blotting and immunohistochemistry. Whereas microcephalin expression did not seem to be altered during glioma development, there was a clear increase in ASPM mRNA and protein expression that corresponded with the WHO grade of the tumor. Our findings are significant as the expression of ASPM may be used as a marker for glioma malignancy and represents a potential therapeutic target.

Expression of matrix metalloproteinases MMP-1, MMP-11 and MMP-19 is correlated with the WHO-grading of human malignant gliomas.

Glioblastomas (GBM) are the most prevalent type of malignant primary brain tumor in adults. They may manifest de novo or develop from low-grade astrocytomas (LGA) or anaplastic astrocytomas. They are characterized by an aggressive local growth pattern and a marked degree of invasiveness, resulting in poor prognosis. Tumor progression is facilitated by an increased activity of proteolytic enzymes such as matrix metalloproteinases (MMPs). Elevated levels of several MMPs were found in glioblastomas compared to LGA and normal brain (NB). However, data for some MMPs, like MMP-1, are controversially discussed and other MMPs like MMP-11 and MMP-19 have as yet not been analysed in detail. We examined the expression of MMP-1, MMP-9, MMP-11 and MMP-19 in NB, LGA and GBM by semiquantitative RT-PCR, Western blotting and immunohistochemistry and found an enhanced expression of these MMPs in GBM compared to LGA or NB in signal strength and in the percentage of tumors displaying MMP expression. The transition from LGA to GBM was characterized by a shift of pro-MMP-11 to expression of the active enzyme. Therefore, MMP-1, MMP-11 and MMP-19 might be of importance for the development of high-grade astrocytic tumors and may be promising targets for therapy.

High efficiency transfection of glioma cell lines and primary cells for overexpression and RNAi experiments.

In order to investigate the impact of signalling proteins on the phenotype and malignant behavior of glioblastoma cells, we optimized the transfection procedure of human glioblastoma cell lines U251, U373, GaMG and of primary cells obtained from a patient's tumor using nucleofection technology in conjunction with plasmid pmaxGFP. We describe the optimization procedure, show that a high percentage of the cells can be transfected and that nucleofection does not cause phenotypic alterations of the cells. Therefore, we conclude that nucleofection is a highly efficient tool to deliver plasmids for transient protein overexpression and siRNA for specific protein knock-down to different glioblastoma cell lines or primary cells.