Abstract
CD9, a member of the tetraspanin superfamily, has been implicated in regulating various physiological processes, including cell motility, adhesion, apoptosis and metastasis. Recently, interleukin-16 (IL-16), a pro-inflammatory cytokine released by normal airway and alveolar epithelial cells, has been implicated as a possible ligand for CD9 as an alternative receptor. In this study, using A549 cells as a model of human alveolar epithelium, CD9 expression was ablated using CRISPR/Cas technology. Decreased expression of CD9 mRNA and protein levels was confirmed through RT-qPCR and flow cytometry, respectively. Individual clones were generated that expressed high levels of CD9 (wild-type, WT) or significantly less CD9 (knockdown, KD). Both wild-type and knockdown A549 cell migration was quantified using a FluoroBloc transwell chemotaxis assay. Our results indicate that wild-type A549 cells migrated towards chemoattractants. Moreover, CD9 expression was required in this process since the CD9 knockdown cells had a significantly reduced migration towards growth serum and IL-16. These results support the migratory properties for CD9 in human lung cells and support the hypothesis that CD9 serves as an alternative receptor for IL-16.