| Gliomas are neoplasms of glial cells and the most prevalent primary tumors of human central nervous system. Despite optimal current therapy, including surgery, radiotherapy, chemotherapy ,etc., most of gliomas, in particular high-grade gliomas, are associated with a poor overall prognosis. So, it is necessary to get further insight into the tumorigenesis of gliomas and search for therapeutic targets for gliomas. One of the focuses in the recent researches on glioma is to identify genes contributing to gliomagenesis. To explore the mechanism of glioma tumorigenesis, the expression of two genes, PEG3 andplakoglobin, was investigated in a series of glioma specimens.Part I Expression of PEGS in GliomasPEG3 (Paternally Expressed Gene 5) is an imprinted gene of which only the paternal allele is expressed. It codes for a large C2H2 type zinc finger protein which may act as a transcription factor. It is expressed in the brain, placenta, ovary, testis, pancreas,etc. The PEG3 protein has been found in the nuclei of both neurons and glial cells. Previous function analyses by other authors have shown PEG3 may be a mediator of TNF signaling pathway and a promotor of apoptosis.Human PEGS gene is located at chromosome 19ql3. And it has been reported that LOH (Loss of Heterozygosity) of 19q is a frequent event in some gliomas. A significant decrease in PEGS expression in 4 of 9 glioma cell lines was observed as compared with that in primary cultures of astrocytes. Transfection of PEGS cDNA into 5 clones of a glioma cell line led to a loss of both anchorage-independent growth in soft agar and tumorigenicity in nude mice. So, PEGS may be a candidate tumor suppressor gene for glioma.Although decreased expression in glioma cell lines has been reported, there is no report, to our knowledge, on how PEGS is expressed in clinical glioma specimens. As genetic changes can take place during the long-term culture of cell lines, it is worth investigating its expression in clinical specimens.In the present study, eighty-one glioma specimens, including 9 grade I astrocytomas, 26 grade II astroytomas, 15 grade IIIanaplastic astrocytomas, 6 grade IV glioblastomas, 6 grade II oligodendrogliomas, 5 grade II ependymomas, 3 grade III anaplastic ependymomas, 7 grade II mixed gliomas and 4 grade III anaplastic mixed gliomas and 11 normal cerebral tissue specimens were snapped frozen for analysis.Total RNA was extracted from samples using TRIzol reagent / chloroform / isopropyl alcohol / ethanol and dissolved in nuclease-free water. After digestion, reextraction, concentration and purity checking, the RNA was reverse transcribed. Using GAPDH as internal control, PCR amplification was carried out and the product was analyzed by agarose gel electrophoresis. The PCR amplification and subsequent agrose gel analysis was repeated to confirm the results.The results showed the RNA was qualified for RT-PCR. All 11 normal brain tissues expressed PEGS at a stable level. No expression was observed in 2/6 cases of oligodendrogliomas. No significant expression change was observed in other subtypes of gliomas compared with normal cerebral tissues. The repeated PCR amplifications and subsequent electrophoresis confirmed these results.Basing on these results, we can conclude:1. PEG3 gene is expressed in normal brain tissue.2. Some oligodendrogliomas (2/6 in this study) show lost expression of PEGS, suggesting PEGS may play a role in the tumorigenesis of this subtype of glioma.3. Other subtypes of gliomas show no significant expression change at the RNA level, and this does not support PEGS as an important candidate tumor suppressor gene for these subtypes of glioma.To our knowledge, this is the first report on the expression of PEGS in clinical glioma specimens.Part II Expression of plakoglobin in Gliomas and Medulloblastomasplakoglobin (i.e. y-catenin, or junction plakoglobin, JUP) is a member of intracellular glycoprotein family called catenin. Like its homologue p-cate...
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