IL-4-induced caveolin-1-containing lipid rafts aggregation contributes to MUC5AC synthesis in bronchial epithelial...

Mucus overproduction is an important feature of asthma. Interleukin (IL)-4 is required for allergen-induced airway inflammation and mucus production. MUC5AC gene expression is regulated by transcript factors NF-κB. The intracellular Ca²⁺ ([Ca²⁺]_i) signal is required for activation of NF-κB. The transient receptor potential canonical 1 (TRPC1) channel has been shown to contribute for agonist-stimulated Ca²⁺ influx in some types of cells. However, the relationships among IL-4, TRPC1 and mucus overproduction in bronchial epithelial cells (BECs) in asthma are poorly understood.

BECs were isolated from large bronchial airway of rats and used as cell model. To present changes of lipid raft, caveolin-1 and TRPC1, immunofluorescence staining and sucrose gradient centrifugation were performed. [Ca²⁺]_i was measured after loading with Fura-2. NF-κB activities were measured by an ELISA-based assay. MUC5AC mRNA and protein levels were detected by real-time quantitative RT-PCR, ELISA analysis and immunofluorescence staining respectively.

IL-4 induced Ca²⁺ influx in BECs, and this was blocked by a Ca²⁺ influx inhibitor (2-APB). 2-APB also prevented MUC5AC protein synthesis induced by IL-4. Depletion of extracellular Ca²⁺ resulted in partial decrease in expression of MUC5AC in IL-4 treated cells. NF-κB rather than STAT6 activation mediated IL-4-induced MUC5AC protein synthesis. Then the mechanism of Ca²⁺ influx was investigated. Immunofluorescence staining and sucrose gradient centrifugation revealed that caveolin-1-containing lipid rafts aggregation was involved in TRPC1 activation and Ca²⁺ influx in BECs. Lastly, the data revealed that blocking lipid rafts aggregation exactly prevented Ca²⁺ influx, NF-κB activation and MUC5AC synthesis induced by IL-4.

Our results indicate that IL-4-induced caveolin-1-containing lipid rafts aggregation at least partly contributes to MUC5AC synthesis in BECs.