Gap junction intercellular communication (GJIC) is essential for regulating the development of the organism and sustaining the internal environmental homeostasis of multi-cellular tissue. Fibroblast growth factor 8 (FGF8), an indispensable regulator of the skeletal system, is implicated in regulating chondrocyte growth, differentiation, and disease occurrence. However, the influence of FGF8 on GJIC in chondrocytes is not yet known. The study aims to investigate the role of FGF8 on cell-cell communication in chondrocytes and its underlying biomechanism. We found that FGF8 facilitated cell-cell communication in living chondrocytes by the up-regulation of connexin43 (Cx43), the major fundamental component unit of gap junction channels in chondrocytes. FGF8 activated p38-MAPK signaling to increase the expression of Cx43 and promote the cell-cell communication. Inhibition of p38-MAPK signaling impaired the increase of Cx43 expression and cell-cell communication induced by FGF8, indicating the importance of p38-MAPK signaling. These results help to understand the role of FGF8 on cell communication and provide a potential cue for the treatment of cartilage diseases.

OBJECTIVE: We aimed to investigate the effects of epidermal growth factor-like domain 7 (EGFL7) on breast cancer cell proliferation and angiogenesis and its association with the p38 mitogen-activated protein kinase (p38MAPK) signaling pathway.
METHODS: The vectors for stable overexpression of EGFL7 and the vectors for EGFL7 knockout were constructed. The breast cancer cell line MDA-MB-231 was selected for this study and the cells were divided into four groups: the control group, the empty vector group (transfected with an empty vector), the EGFL7 overexpression group (transfected with the EGFL7 overexpression vector), and the EGFL7 knockout group (transfected with the EGFL7 knockout vector). After 72 h of transfection, the mRNA and protein levels of EGFL7 in the cells were detected by RT-PCR and Western blot, respectively. The cell proliferation rates at 12 h, 24 h, 48 h and 72 h of culture in each group were detected using the MTT method. An in vitro tumor angiogenesis model of tumor-endothelial cells co-culture system was established and the angiogenesis ability at 12 h, 24 h, 48 h and 72 h of culture were compared among the groups using an in vitro angiogenesis assay. The cells in the EGFL7 overexpression group were further divided into three groups and were treated with p38MAPK inhibitor SB203580 at a dose of 0 μmol/L, 5 μmol/L, and 10 μmol/L, respectively. Afterward, the cells were co-cultured with endothelial cells for 48 h. Western blot was performed to detect the protein levels of vascular endothelial growth factor (VEGF), p38MAPK, and p-p38MAPK.
RESULTS: Compared with the control group, the EGFL7 mRNA level was higher in the EGFL7 overexpression group and lower in the EGFL7 knockout group (both P<0.05). Compared with the control group at 12 h, 24 h, 48 h, and 72 h of culture, the cell proliferation rates were lower in the EGFL knockout group and higher in the EGFL overexpression group, respectively (all P<0.05). Moreover, compared with the control group at these time points, the number of vascular sprouts and the protein levels of VEGF, p38MAPK, and p-p38MAPK were lower in the EGFL7 knockout group and higher in the EGFL7 overexpression group, respectively (all P<0.05). After the cells overexpressing EGFL7 were treated with SB203580, the level of p-p38MAPK was deceased, and the protein expression level of VEGF was inversely related with the SB203580 concentration (F=44.24, P<0.01).
CONCLUSIONS: EGFL7 can promote the proliferation of breast cancer cells and angiogenesis, and the mechanism may be associated with the activation of p38MAPK signaling pathway and promotion of VEGF expression.

Porcine circovirus 2 (PCV2) has been proved to increase the risk of other pathogens infection via immunosuppression. Although the co-infection of PCV2 and porcine parvovirus (PPV) is commonly observed in worldwide, the relative immune mechanisms promoting PPV infection in PCV2-infected piglets are currently unknown. Herein, we found that PCV2 infection suppressed IFN-β expression and promoted PPV infection in the piglets. Consistent with this finding, we confirmed that PCV2 infection significantly inhibited the induction of IFN-β to promote PPV replication in cell level. Furthermore, PCV2 infection attenuated the K63-linked ubiquitination of STING induced by PPV, blocked the formation of complex of STING, TBK1 and IRF3, and further prevented the phosphorylation of TBK1 and IRF3, resulting in a decreased IFN-β transcription response to PPV infection. Consistently, using cGAMP to direct stimulate STING also appeared a reduced STING-K63 ubiquitination and IFN-β induction in PCV2-infected cells. However, we noted that knockdown of p38-MAPK signaling could markedly attenuate the inhibitory effect of PCV2 on STING-K63 ubiquitination, and improve the induction of IFN-β in PCV2-infected whenever theses cells were challenged with PPV infection or cGAMP stimulation. Meanwhile, we found that PCV2 infection promoted the phosphorylation of USP21 to inhibit the K63 ubiquitination of STING and the transcription of IFN-β via activation of p38-MAPK signaling. Taken together, our results demonstrate that PCV2 infection activates the p38-MAPK signaling pathway-mediated USP21 phosphorylation to inhibit the K63 ubiquitination of STING, which prevents the phosphorylation and transportation to the nucleus of IRF3, leading to an increase risk for PPV infection.

The tumor suppressor liver kinase B1 (LKB1), a highly conserved and ubiquitously expressed protein kinase, plays a critical role in tumorigenesis. LKB1 has recently been identified in tumorigenesis of several cancers including lung cancer, breast cancer, and pancreatic cancer. However, the role of LKB1 in hepatocellular carcinoma (HCC) remains unclear. Herein, we examined the expression levels of LKB1 in HCC patients and cell lines by quantitative real-time PCR (qRT-PCR) and western blot analysis. Furthermore, LKB1 protein expression was analyzed in archived paraffin-embedded HCC tissues using immunohistochemistry (IHC), and its association with overall survival was shown in statistical analysis. In vitro assays, including RNAi studies, were performed to further explore the role of LKB1 in tumor progression in HCC cell lines. Our results revealed that the expression of LKB1 was lower in HCC tissue and cell lines than in corresponding adjacent normal tissue and normal human liver cell line (HL7702). Moreover, HCC patients with low LKB1 expression had advanced clinical stage and worse prognosis than those with higher LKB1 expression. Furthermore, siRNA-mediated knockdown of LKB1 resulted in enhanced cell proliferation, migration, and invasion of HCC cells. Additionally, the expression level of LKB1 positively correlated with E-cadherin levels, wherein siRNA-transfected cells exhibited significantly decreased levels of E-cadherin, while phosphorylated p38 and vimentin levels were enhanced. Inhibition of p38 MAPK signaling was capable of reversing E-cadherin up-regulation and vimentin down-regulation. In all, our results indicate that LKB1 acts as a tumor suppressor gene, which may inhibit EMT through the p38 MAPK signaling pathway involved in HCC progression.