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Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

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6.7 Is<strong>of</strong>orm Differential Expression Results<br />

Table 6.8: MicroRNA array results for GNS cell lines with respect to NS cell lines.<br />

Based on a literature survey, these microRNAs would be interesting candidates to<br />

validate experimentally in a TLDA assay.<br />

microRNA log 2(F C) FDR<br />

miR-128 0.9 0.000206443<br />

miR-137 1 0.000121777<br />

miR-34a -1.5 0.000004.43<br />

miR-26a 1.4 0.0000143<br />

miR-10b 2.9 1.03E-08<br />

miR-451 1 3.15E-05<br />

miR-129-3p 1 9.63E-05<br />

· The levels <strong>of</strong> miR-128 have been found to be consistently lower in<br />

glioblastoma compared with normal brain tissue [259,364]. Opposite<br />

findings were observed in our microRNA array, in which miR-128 is up-<br />

regulated in GNS cells with respect to NS cells (Table 6.8). miR-128<br />

directly targets the transcription factor E2F3a, which activates genes<br />

necessary for the progression <strong>of</strong> cell-cycle and can thus inhibit prolifera-<br />

tion <strong>of</strong> brain cells by negatively regulating E2F3a. This microRNA also<br />

directly targets BMI1, a gene that is thought to act as an oncogene in<br />

glioblastoma by regulating tumour suppressors like P53 and CDKN2A.<br />

BMI1 also promotes stem cell renewal by acting as part <strong>of</strong> a Polycomb Si-<br />

lencing Complex to silence the expression <strong>of</strong> genes - including CDKN2A<br />

and CDKN1A tumour suppressors - involved in differentiation and senes-<br />

cence. Low levels <strong>of</strong> miR-128 in glioblastoma may contribute to glioma<br />

growth by allowing the increased expression <strong>of</strong> BMI1 to promote an un-<br />

differentiated self-renewing state. High levels <strong>of</strong> miR-128 in GNS cells<br />

with respect to NS cells may identify a stem cell pool specific regulation<br />

that has yet to be studied in detail. miR-128 is known to be highly<br />

expressed in neurons but its role in the brain is still unknown and is<br />

surmised to be the promotion <strong>of</strong> neuronal differentiation through pre-<br />

vention <strong>of</strong> stem cell self-renewal. Our is<strong>of</strong>orm data analysis with the<br />

non-parametric method showed that miR-128 is predicted to target the<br />

nerve growth factor receptor associated protein 1 NGFRAP1, a p75NTR-<br />

associated cell-death executor mediated by the common neutrophin re-<br />

ceptor p75NTR [350] that also plays a role in NGF-induced apopto-<br />

sis in oligodendrocytes [351]. Analsysis with the logarithmic method<br />

showed that miR-128 is predicted to target the Rab GTPase guanine nu-<br />

152

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