Figure 3.

The EGFR-ERK pathway inhibits JNK activities. HaCaT cells treated with vehicle (DMSO, Ctl) and TCDD (T, 10 nM) in the presence or absence of the EGFR inhibitor, AG1478 (AG, 10 μM), were (A) subjected to immunoblotting for p-EGFR, p-ERK, p-JNK, total JNK, and β-actin, and (B) quantification for p-JNK using β-actin as a loading control. HaCaT cells treated with different concentrations of an ERK inhibitor, PD98059 (PD), and a JNK inhibitor, SP600125 (SP) were (C) examined by immunoblotting for p-ERK, p-JNK, and β-actin, and values of (D) p-ERK and (E) p-JNK were quantified and compared to that of β-actin. F, p-JNK, p-ERK, and β-actin were examined by immunoblotting in lysates of HaCaT cells treated with TCDD (T, 10 nM) in the presence and absence of phosphatase inhibitor Na₃VO₄ (0.5 mM). Values of relative p-JNK and p-ERK were quantified using β-actin. G, expression of DUSP4 and PTPRE was examined by qRT-PCR in HaCaT cells treated with vehicle (DMSO, Ctl) and TCDD (T, 10 nM) in the presence and absence of 10 μM AG and PD. Relative mRNA of DUSP4 and PTPRE was calculated using GAPDH as an internal control. Value of Ctl sample was set as 1. Data were shown as mean ± SEM of at least three independent experiments (N ≥ 3). ∗p < 0.05, ∗∗p < 0.01 and ∗∗∗p < 0.001 were considered significantly different compared to Ctl (in B, D, E, and G) and TCDD-treated cells (in F). DMSO, dimethyl sulfoxide; DUSP4, dual specificity phosphatase 4; EGFR, epidermal growth factor receptor; ERK, extracellular signal regulated kinase; JNK, Jun N-terminal kinase; PTPRE, protein tyrosine phosphatase epsilon; qRT-PCR, quantitative reverse transcription PCR; TCDD, 2,3,7,8-tetrachlorodibenzo-para-dioxin.