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. 2013 May 15;41(13):6618–6636. doi: 10.1093/nar/gkt410

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© The Author(s) 2013. Published by Oxford University Press.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited

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Figure 2. — IGF2BP1 promotes LEF1 expression by preventing LEF1 mRNA degradation. (A and B) HEK293 cells were transfected with control (siC) or indicated IGF2BP1-directed (siI1-1, siI1-2) siRNAs for 72 h. Protein abundance on IGF2BP1 knockdown was determined relative to controls (siC) by western blotting using VCL and TUBA4A for cross-normalization, as indicated above panels. Representative western blots of three independent analyses are shown. ACTB and LEF1 mRNA levels were analyzed by qRT-PCR. Changes in RNA abundance on IGF2BP1 knockdown (siIGF2BP1) were determined relative to controls (siC) by the ΔΔC_t-method using PPIA for normalization. (C) RNA decay was monitored in HEK293 cells transfected with indicated siRNAs for 72 h by blocking mRNA synthesis using ActD (5 µM) for indicated times. RNA levels were determined by qRT-PCR using normalization to PPIA by the ΔΔC_t-method. RPLP0 served as a control. RNA decay is depicted in semi-logarithmic scale. Statistical significance determined over three independent analyses was analyzed by Student’s t-test, as shown in panels (P-values). (D and E) The association of indicated mRNAs with IGF2BP1 in HEK293 cells was analyzed by RIP using formaldehyde fixation to stabilize mRNPs prior purification. Endogenous IGF2BP1 was immunopurified (I1) by a monoclonal antibody, as indicated by western blotting in the lower panel (IB). Co-purification of indicated mRNAs was analyzed relative to the input fraction (I, 10% of cell lysates) by semi-quantitative (D) as well as qRT-PCR (E). IgG-agarose served as a control (C) for unspecific mRNA binding. The enrichment of mRNAs by immunopurification of IGF2BP1 (I1) was determined relative to the input fraction by using the ΔC_t-method (E). (F) Upper panel: Scheme of used Firefly reporters comprising the two alternative LEF1 3′-UTRs (A: Acc.No., NM_016269 /001130713/ 001166119; B: Acc.No., NM_001130714) or the vector-encoded BGH-3′UTR (C). Lower panel: HEK293 cells were transfected with control or indicated IGF2BP1-directed siRNAs for 48 h before the co-transfection of Firefly luciferase reporters (A–C: see scheme in upper panel) and Renilla luciferase control reporters for 24 h. Changes in Firefly luciferase reporter activities on IGF2BP1 knockdown (siIGF2BP1) were determined relative to controls (siC) on normalization by Renilla activities. Statistical significance was validated by Student’s t-test: *P < 0.05; **P < 0.005; ***P < 0.0005. Error bars indicate SD of at least three independent analyses.