Abstract
BackgroundWith current treatment strategies, nearly half of all medulloblastoma (MB) patients die from progressive tumors. Accordingly, the identification of novel therapeutic strategies remains a major goal. Deregulation of c-MYC is evident in numerous human cancers. In MB, over-expression of c-MYC has been shown to cause anaplasia and correlate with unfavorable prognosis.MethodsTo study the role of c-MYC in MB biology, we down-regulated c-MYC expression by using small interfering RNA (siRNA) and investigated changes in cellular proliferation, cell cycle analysis, apoptosis, telomere maintenance, and response to ionizing radiation (IR) and chemotherapeutics in a representative panel of human MB cell lines expressing different levels of c-MYC (DAOY wild-type, DAOY transfected with the empty vector, DAOY transfected with c-MYC, D341, and D425).ResultssiRNA-mediated c-MYC down-regulation resulted in an inhibition of cellular proliferation and clonogenic growth, inhibition of G1-S phase cell cycle progression, and a decrease in human telomerase reverse transcriptase (hTERT) expression and telomerase activity. On the other hand, down-regulation of c-MYC reduced apoptosis and decreased the sensitivity of human MB cells to IR, cisplatin, and etoposide. This effect was more pronounced in DAOY cells expressing high levels of c-MYC when compared with DAOY wild-type or DAOY cells transfected with the empty vector.ConclusionIn human MB cells, in addition to its roles in growth and proliferation, c-MYC is also a potent inducer of apoptosis. Therefore, targeting c-MYC might be of therapeutic benefit when used sequentially with chemo- and radiotherapy rather than concomitantly.
Highlights
With current treatment strategies, nearly half of all medulloblastoma (MB) patients die from progressive tumors
Transfection of human MB cells with small interfering RNA (siRNA) directed against c-MYC resulted in a pronounced downregulation of c-MYC mRNA expression to 21% in DAOY wt (p < 0.001), 22% in DAOY V11 (p < 0.001), 6% in DAOY M2 (p < 0.001), 33% in D341 (p < 0.001), and 65% in D425 (p = 0.017) compared with negative control siRNA-transfected cells, as determined by quantitative RTPCR at 48 h following transfection (Figure 1A)
Transfection of human MB cells with c-MYC siRNA resulted in a significant reduction of c-MYC binding activation to 10% in DAOY wt (p = 0.015), 28% in DAOY V11 (p = 0.009), 21% in DAOY M2 (p = 0.008), 74% in D341 (p = 0.05), and 63% in D425 (p = 0.03), compared with MB cells transfected with negative control siRNA at 72 h following transfection (Figure 1C)
Summary
Nearly half of all medulloblastoma (MB) patients die from progressive tumors. Deregulation of c-MYC is evident in numerous human cancers. Nearly half of all patients eventually die from progressive tumors. Deregulated expression of c-MYC is often associated with aggressive, poorly differentiated tumors [4]. Deregulation of c-MYC expression is evident in MB with c-MYC gene amplification or aberrant signal transduction of wingless (WNT) signaling pathway [18]. In MB, high c-MYC mRNA expression and c-MYC gene amplification have been described as indicators of poor prognosis [19,20,21,22]. Two studies have demonstrated that high cMYC mRNA expression is associated with tumor anaplasia [23,24]
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