Characterization of the roles of the RNA-binding protein AUF-1 in airway epithelial inflammatory responses

The RNA-binding protein AU-rich-element factor-1 (AUF-1) regulates mRNA decay and translation of genes during inflammation and cellular senescence, two pathogenic mechanisms of chronic obstructive pulmonary disease (COPD). Decreased AUF-1 expression was described in bronchiolar epithelium of COPD patients versus controls and in vitro cytokine-challenged airway epithelial cells, prompting the identification of epithelial AUF-1-targeted transcripts and function. RNA immunoprecipitation-sequencing (RIP-Seq) identified, in the human BEAS-2B cell line, 494 AUF-1-bound mRNAs enriched in their 3’-untranslated regions for a Guanine-Cytosine (GC)-rich binding motif, selectively confirmed by biotin pulldown. AUF-1-targets’ steady-state levels were equally affected by partial or near-total AUF-1 loss induced by cytomix (TNF/IL1/IFN/10 nM each) and siRNA, respectively, with differential transcript decay rates. Cytomix-decreased AUF-1 levels in BEAS-2B and primary human small-airways epithelium (HSAEC) associated with cell-cycle arrest, increased lysosomal damage and senescence-associated secretory phenotype (SASP) factors and with increased AUF-1 in extracellular vesicles. In-silico analysis found enriched AUF-1-targets in COPD-related pathways, SASP proteome atlas, transcriptomic COPD databases of HSAEC, lung tissue and single-cell RNA-sequencing. Intracellular and exosomal-associated AUF-1 may mediate airway epithelial inflammatory responses.