In addition, the above cytokines are beneficial for fibroblasts to produce type I collagen, which is the main component in skin fibrosis, wound healing, tissue remodeling, and skin aging [47]. cell proliferation. GW 6471 The results showed that 3? 0.05 were considered statistically significant, and differences with 0.01 were considered extremely significant. 3. Results 3.1. DP Promoted Fibroblast Proliferation Fibroblasts were treated with different concentrations (0.5, 1, 1.5, 2, GW 6471 2.5, 3, 3.5, and 4? 0.01 vs. control group) and DP promoted fibroblast proliferation significantly compared with that of the control group when DP was more than 0.5? 0.01), with a peak at 3? 0.01). Moreover, under DP treatment, cell proliferation was enhanced in a time-dependent manner. At 24?h, DP-induced cell proliferation was the most obvious. In these three drug-treated groups, DP at 3? 0.05; 0.01 vs. control group at the same time). 3.2. DP Promoted Cell Cycle Progression in Fibroblast Cells Generally, fibroblast proliferation is usually closely related to the cell cycle. Therefore, we examined the cell cycle in DP-treated fibroblasts. The cell proliferation index (proliferation index, PI?=?S?+?G2/M) NOTCH2 represents the number of proliferating cells in the cell populace. The G2/M phase is the late stage of DNA synthesis, and DNA completes self-replication in S phase, which reflects the state of cell proliferation to some extent. Fibroblasts were treated with different concentrations (2, 3, and 4? 0.01) and increased the number GW 6471 of cells in the S ( 0.01) and G2/M ( 0.01) phases compared to that of the control group (Physique 3(a)). Additionally, PI was significantly increased ( 0.01; Physique 3(b)). With DP treatment at 3? 0.05, 0.01 compared with controls by Student’s 0.01); however, no change was found in p-FGFR ( 0.05). Open in a separate GW 6471 window Physique 4 DP activated EGFR, ERK1/2, and PI3K signaling pathways in fibroblasts. (a) After the cells were treated with DP, the expression of p-EGFR/EGFR, p-FGFR/FGFR, p-ERK/ERK, p-JNK/JNK, p-CREB/CREB, p-PI3K/PI3K, p-Akt/Akt, and p-mTOR/mTOR was analyzed by immunoblotting. (b) Gray intensity was measured using ImageJ software at different time points, and the phosphorylation levels of related proteins were calculated and shown in Physique 4(b) (data are presented as means??SD, 0.05, and double symbols, such as 0.01 vs. control group). The EGFR signaling pathway downstream involves the MAPK and PI3K families. ERK1/2 and JNK, as MAPK family members, play important functions in the control of cell proliferation. In our further studies, p-ERK extremely increased after DP treatment in a time-dependent manner ( 0.01). P-JNK had no obvious changes ( 0.05). Because phosphorylated ERK1/2 is known to phosphorylate transcription factors, such as CREB, which regulates the transcription of genes involved in cell metabolism, growth, migration, and proliferation, we next examined the effects of DP on CREB phosphorylation. Similar to the effects that were previously observed, CREB phosphorylation was also significantly increased at 15, 30, and 60?min with DP ( 0.01). On the other hand, we further assessed PI3K and its downstream protein (Akt/mTOR) phosphorylation levels. The level of p-PI3K showed a time-dependent increase after treatment with DP ( 0.01). Comparable results were also discovered in the levels of AKT/p-AKT and mTOR/p-mTOR ( 0.01). These results exhibited that DP activated EGFR, ERK1/2, and PI3K signaling pathways. 3.4. Related Inhibitors Suppressed DP-Induced Signaling Pathway Activation According to the above experimental results, we GW 6471 added signaling pathway inhibitors into cell-cultured plates to pretreat fibroblasts. The aim of this was to determine the involvement of EGFR, ERK1/2-CREB, and PI3K/Akt/mTOR activation in DP-induced protein phosphorylation. The results showed that EGFR inhibitor (AG1478) inhibited DP-promoted EGFR phosphorylation, and then the ERK and PI3K families were not activated by DP as they were in the control group ( 0.05, Figures 5(a) and 5(b)). The phosphorylation levels of JNK did not increase compared to those of the control group ( 0.05, Figures 5(a) and 5(b)). In Figures 5(c) and 5(d), the cells pretreated by ERK inhibitors (U0126) significantly depressed DP-induced ERK and CREB phosphorylation, which had no changes compared to that of the control group ( 0.05)..