Nucleolin enhances internal ribosomal entry site (IRES)-mediated translation of Sp1 in tumorigenesis

Chia-Yang Hung; Wen-Bin Yang; Shao-An Wang; Tsung-I Hsu; Wen-Chang Chang; Jan-Jong Hung

doi:10.1016/j.bbamcr.2014.08.009

Nucleolin enhances internal ribosomal entry site (IRES)-mediated translation of Sp1 in tumorigenesis

Biochim Biophys Acta. 2014 Dec;1843(12):2843-54. doi: 10.1016/j.bbamcr.2014.08.009. Epub 2014 Aug 27.

Authors

Chia-Yang Hung¹, Wen-Bin Yang², Shao-An Wang², Tsung-I Hsu³, Wen-Chang Chang⁴, Jan-Jong Hung⁵

Affiliations

¹ Institute of Basic Medical Sciences, College of Medicine, National Cheng-Kung University, Tainan, Taiwan.
² Institute of Bioinformatics and Biosignal Transduction, College of Bioscience in Biotechnology, National Cheng-Kung University, Tainan, Taiwan.
³ Department of Pharmacology, College of Medicine, National Cheng-Kung University, Tainan, Taiwan; Institute of Bioinformatics and Biosignal Transduction, College of Bioscience in Biotechnology, National Cheng-Kung University, Tainan, Taiwan; Center for Infection Disease and Signal Transduction, National Cheng-Kung University, Tainan, Taiwan.
⁴ Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
⁵ Institute of Basic Medical Sciences, College of Medicine, National Cheng-Kung University, Tainan, Taiwan; Department of Pharmacology, College of Medicine, National Cheng-Kung University, Tainan, Taiwan; Institute of Bioinformatics and Biosignal Transduction, College of Bioscience in Biotechnology, National Cheng-Kung University, Tainan, Taiwan; Center for Infection Disease and Signal Transduction, National Cheng-Kung University, Tainan, Taiwan; Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan. Electronic address: [email protected].

PMID: 25173817
DOI: 10.1016/j.bbamcr.2014.08.009

Abstract

Our previous study indicated that specificity protein-1 (Sp1) is accumulated during hypoxia in an internal ribosomal entry site (IRES)-dependent manner. Herein, we found that the Sp1 was induced strongly at the protein level, but not in the mRNA level, in lung tumor tissue, indicating that translational regulation might contribute to the Sp1 accumulation during tumorigenesis. A further study showed that the translation of Sp1 was dramatically induced through an IRES-dependent pathway. RNA immunoprecipitation analysis of proteins bound to the 5'-untranslated region (5'-UTR) of Sp1 identified interacting protein - nucleolin. Knockdown of nucleolin significantly inhibited IRES-mediated translation of Sp1, suggesting that nucleolin positively facilitates Sp1 IRES activation. Further analysis of the interaction between nucleolin and the 5'-UTR of Sp1 mRNA revealed that the GAR domain was important for IRES-mediated translation of Sp1. Moreover, gefitinib, and LY294002 and MK2206 compounds inhibited IRES-mediated Sp1 translation, implying that activation of the epithelial growth factor receptor (EGFR) pathway via Akt activation triggers the IRES pathway. In conclusion, EGFR activation-mediated nucleolin phosphorylated at Thr641 and Thr707 was recruited to the 5'-UTR of Sp1 as an IRES trans-acting factor to modulate Sp1 translation during lung cancer formation.

Keywords: EGFR; IRES; Nucleolin; Phosphorylation; Sp1.