Some viral proteins were translated in cap-independent manner via internal ribosome entry site (IRES), which ever maintained conservative characteristic among different isolates of same species of virus. However, IRES activity presented 7-fold of variance in RNA2 of wheat yellow mosaic virus (WYMV) HC and LYJN isolates. Based on RNA structure probing and mutagenesis assay, the loosened middle stem of H1 and hepta-nucleotide top loop of H2 in LYJN isolate synergistically ensured the higher IRES activity than that in HC isolate. In addition, the conserved top loop of H1 ensured basic IRES activity in HC and LYJN isolates. RNA2 5′-UTR specifically interacted with the wheat eIF4E, which was accomplished by the top loop of H1 in HC isolate or the top loop of H1 and H2 in LYJN isolate. Different IRES activity of WYMV RNA2 was regulated by different numbers of eIF4E-binding site and their synergistic effect, which was accomplished by the proximity of H1 and H2 due to the flexibility of middle stem in H1. It is represented a novel evolution pattern of IRES.

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15031 Background: Our previous studies show that human carcinoid cells overexpress pro-angiogenic factors, vascular endothelial growth factor A (VEGF), and transcription factor Sp1 plays a critical role in VEGF inducible and constitutive expression. However, the impact of antiangiogenic therapy on the Sp1/VEGF pathway remains unclear. Method: Groups of 10 athymic BALB/c nude mice were implanted with 1.5 million human H727 carcinoid cells. Treatment with VEGF neutralizing monoclonal antibody, BEV, MIT, or BEV + MIT was initiated once implanted tumor reached 4 mm in size. Result: Treatment with BEV, suppressed human carcinoid growth in nude mice (tumor size at week 5 1280 mm3 vs 480 mm3; p < 0.001). Gene expression analyses revealed that this treatment substantially upregulated the expression of Sp1 (7 folds) and its downstream target genes, including VEGF (5 folds) and epidermal growth factor receptor (4 folds), in tumor tissues, whereas it did not have this effect on carcinoid cells in culture. Treatment with mithramycin A, an Sp1 inhibitor, suppressed the expression of Sp1 and its downstream target genes in both cell culture and tumors growing in nude mice. Median survival of mice treated with PBS, BEV, MIT, and BEV + MIT groups were 88, 112, 121, and >160 days respectively (p < 0.001). Combined treatment with bevacizumab and mithramycin A produced synergistic tumor suppression, which was consistent with suppression of the expression of Sp1 and its downstream target genes. Conclusion: Treatment with bevacizumab may block VEGF function but activate the pathway of its expression via positive feedback. Given the fact that Sp1 is an important regulator of the expression of multiple angiogenic factors, bevacizumab-initiated upregulation of Sp1 and subsequent overexpression of its downstream target genes may affect the potential angiogenic phenotype and effectiveness of antiangiogenic strategies for human carcinoid. No significant financial relationships to disclose.