Fig. 4.

EGFR-pERK1/2-AP1 pathway was triggered by viral infection. a: Quantitative real-time RT-PCR analysis of EGFR (solid line, left y axis) and MUC15 (dotted line, right y axis) mRNA expression in hNECs infected with H3N2 (n = 11), using PGK1 as the internal control. Relative mRNA expression levels were calculated using 2^ ^(−ΔΔCt) method; the fold change was compared against uninfected control subjects. b: The correlations between protein level (blot band intensities) of MUC15 versus EGFR in hNECs with or without H3N2 infection were analyzed (n = 5). c: Western blot analysis of EGFR, pERK, total ERK and GAPDH protein expression on hNECs with or without H3N2infection. Cells were harvested at various times as indicated (n = 5). d: Quantitative real-time RT-PCR analysis of JUN and FOS mRNA expressions in hNECs with or without H3N2 infection (n = 11), using PGK1 as the internal control. Relative mRNA expression levels were calculated using 2^ ^(−ΔΔCt) method; the fold change was compared against uninfected control subjects. e: The correlations between mRNA level (2^ ^(−ΔΔCt)) of MUC15 versus JUN and FOS in hNECs infected with H3N2 were analyzed (n = 11). f: The hypothesis of MUC15’s potential role in hNECs infected with H3N2: The increase of MUC15 expression triggered by H3N2 viral replication inhibits the activation of epithelial growth factor receptor (EGFR), which initiates the downstream ERK1/2-AP1 pathway. Thus, MUC15 may downregulate the host immune response at the later phase of viral infection. *, **, ***, **** denotes P value of less than 0.05, 0.01, 0.001, < 0.0001 compared with uninfected control, respectively. Uni: uninfected control