TERT and its binding protein: overexpression of GABPA/B in high grade gliomas

Abstract

Enhanced expression of TERT in gliomas is a result of two hotspot mutations, C228T and C250T, at the promoter region. GA-binding proteins selectively bind at these positions, respectively, causing an activation of the promoter and overexpression of TERT. GABP is a multimeric protein consisting of GABPA and GABPB with its isoforms GABPB1, GABPB1-L, GABPB1-S, GABPB2. In this study, we investigated the mRNA expression and association between TERT and GABPA/B isoforms in tumor samples of different glioma grades. The expression was determined by quantitative real-time PCR and the results were statistically analyzed. We present that TERT is mainly expressed in primary glioblastomas. All GA-binding proteins progress through the glioma grades and have the highest expression levels in secondary glioblastomas. In secondary glioblastomas after chemotherapy, GABPB1 and GABPB1-L are expressed on a lower level than without treatment. In high grades, TERT and GABPA, GAPB1, GABPB1-L, GABPB1-S are upregulated compared to low grades. Between primary and secondary glioblastomas with and without chemotherapy, TERT is elevated in the former while GABPB1 is increased in the secondary glioblastomas. GABPA and GABPB1, GABPB1-L and GABPB1-S positive correlate in primary glioblastomas. The present study confirms the upregulation of TERT in primary glioblastomas while all GABP proteins rise with the malignancy of the gliomas. Further investigations must be made to elucidate the relation between TERT and all GABP proteins as it may play a key role in the gliomagenesis.

Keywords: GABPA; GABPB; TERT; astrocytoma; glioma.

Figure 1

mRNA expression levels of (A) TERT, (B) GABPA, (C) GABPB1, (D) GABPB1–L, (E) GABPB1–S and (F) GABPB2 by quantitative real – time PCR in controls, glioma grade II, grade III, secondary glioblastomas (sec. GBM), recurrent secondary glioblastomas treated with chemotherapy (sec. GBM + CTx), primary glioblastoma (prim. GBM) and primary glioblastoma treated with chemotherapy (prim. GBM + CTx). Columns display the mean values [arbitrary units] and error bars the standard deviations. Statistically significance is marked with ^* p < 0.05, ^** p < 0.01, ^*** p < 0.001 and ^**** p < 0.0001.

Figure 2. Comparison of TERT, GAPBA, GAPB1, GABPB1–L, GABPB1–S and GABPB2 mRNA expression levels between low grade (WHO II) and high grade gliomas (WHO III and secondary glioblastomas).

(A) Overexpression of TERT in high grade gliomas. (B–E) Increased levels of GABPA, GAPB1, GABPB1–L, GABPB1–S in high grades. (F) GABPB2 shows no significant difference. Columns display the mean values and error bars the standard deviation. Statistical significance is marked with ^* p < 0.05, ^*** p < 0.001 and ^**** p < 0.0001, n.s.: no significance.

Figure 3. TERT and GABPA/B isoforms mRNA expressional status between primary and secondary glioblastomas with and without chemotherapy.

(A) TERT is overexpressed in primary glioblastomas with p < 0.0001. (B) GABPB1 is highly expressed in secondary glioblastomas, p = 0.043. (C–F) No significant difference in GABPA, GABPB1–L, GABPB1–S and GABPB2. Columns display the mean values and error bars the standard deviation. Statistical significance is marked with ^* p < 0.05 and ^**** p < 0.0001, n.s.: no significance.

Figure 4. Correlation of TERT vs. GABPB1/-S and GABPB1, GABPB1-L, GABPB1-S and GABPB2 vs. GABPBA mRNA expression in gliomas.

Black line indicates trend-line and Pearson’s rank order correlation was used to generate Pearson rho and p-values for each correlation. (A) No correlation between TERT and moreover, in primary glioblastomas (r = 0.18). (B) negative linear correlation between TERT and in addition, in grade III gliomas (r = –0.65, p = 0.003). (C–E) GABPA correlates positive with GABPB1, GABPB1-L and GABPB1-S in primary glioblastomas with p = 0.035, 0.0008 and 0.045, respectively. (F) GABPA and GABPB2 have the tendency to slightly positive correlate in primary glioblastomas, without any statistical significance, n.s.: no significance.