Open AccessNovel AU-rich proximal UTR sequences (APS) enhance CXCL8 synthesis upon the induction of rpS6 phosphorylation
Author(s) -
Zhiwei Ang,
Ricky Abdi Gunawan Koean,
Jun Zhi Er,
Li Ting Lee,
John Kit Chung Tam,
Huili Guo,
Jeak Ling Ding
Publication year - 2019
Publication title -
plos genetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.587
H-Index - 233
eISSN - 1553-7404
pISSN - 1553-7390
DOI - 10.1371/journal.pgen.1008077
Subject(s) - biology , microbiology and biotechnology , phosphorylation , untranslated region , interleukin 8 , three prime untranslated region , translation (biology) , ribosomal protein s6 , messenger rna , protein kinase b , cytokine , gene , immunology , genetics , p70 s6 kinase 1
The role of ribosomal protein S6 (rpS6) phosphorylation in mRNA translation remains poorly understood. Here, we reveal a potential role in modulating the translation rate of chemokine (C-X-C motif) ligand 8 ( CXCL8 or Interleukin 8, IL8 ). We observed that more CXCL8 protein was being secreted from less CXCL8 mRNA in primary macrophages and macrophage-like HL-60 cells relative to other cell types. This correlated with an increase in CXCL8 polyribosome association, suggesting an increase in the rate of CXCL8 translation in macrophages. The cell type-specific expression levels were replicated by a CXCL8- UTR-reporter (Nanoluc reporter flanked by the 5’ and 3’ UTR of CXCL8 ). Mutations of the CXCL8 -UTR-reporter revealed that cell type-specific expression required: 1) a 3’ UTR of at least three hundred bases; and 2) an AU base content that exceeds fifty percent in the first hundred bases of the 3’ UTR immediately after the stop codon, which we dub AU-rich proximal UTR sequences (APS). The 5’ UTR of CXCL8 enhanced expression at the protein level and conferred cell type-specific expression when paired with a 3’ UTR. A search for other APS-positive mRNAs uncovered TNF alpha induced protein 6 ( TNFAIP6 ), another mRNA that was translationally upregulated in macrophages. The elevated translation of APS-positive mRNAs in macrophages coincided with elevated rpS6 S235/236 phosphorylation. Both were attenuated by the ERK1/2 signaling inhibitors, U0126 and AZD6244. In A549 cells, rpS6 S235/236 phosphorylation was induced by TAK1, Akt or PKA signaling. This enhanced the translation of the CXCL8 -UTR-reporters. Thus, we propose that the induction of rpS6 S235/236 phosphorylation enhances the translation of mRNAs that contain APS motifs, such as CXCL8 and TNFAIP6 . This may contribute to the role of macrophages as the primary producer of CXCL8, a cytokine that is essential for immune cell recruitment and activation.