Inhaltszusammenfassung

Extracellular signal-regulated kinase 3 (ERK3) is a member of mitogen-activated protein kinases (MAPKs) and along with ERK4 and MK5 constitutes one of the less understood atypical MAPK modules. Recently, ERK3 gained due attention for its role in mediating tumor cell migration and metastasis. As the molecular mechanisms regulating ERK3 expression and function are unclear, the aim of this study is to decipher the activation dynamics and functional significance of this atypical MAPK. In this stu...Extracellular signal-regulated kinase 3 (ERK3) is a member of mitogen-activated protein kinases (MAPKs) and along with ERK4 and MK5 constitutes one of the less understood atypical MAPK modules. Recently, ERK3 gained due attention for its role in mediating tumor cell migration and metastasis. As the molecular mechanisms regulating ERK3 expression and function are unclear, the aim of this study is to decipher the activation dynamics and functional significance of this atypical MAPK. In this study, we primarily aimed to evaluate the role of ERK3 in regulating innate immune responses. Loss of function studies revealed a critical role of ERK3 in the control of LPS-regulated gene expression in epithelial cells. During the course of this study, we detected that CXCL8/IL-8 expression is strictly reliant on the expression of ERK3 in human colonic primary epithelial cells as well as in cancer cell lines. ERK3 controls IL-8 production and secretion in a kinase independent manner. It was further characterized that IL-8 promoter activity is dependent on ERK3 and several known transcription factors that control IL-8 expression are regulated by ERK3. Moreover, ERK3 plays a critical role in AP-1 signaling by interacting with and regulating nuclear localization of c-Jun protein in response to LPS. Furthermore, ERK3 also regulates MCP-1 (Monocyte chemoattractant protein-1), GCP-2 (Granulocyte chemotactic protein-2) or CXCL10, which are critically required for maintaining proper epithelial secretome and leukocytes chemotaxis in vitro and in vivo. We also detect that LPS elicits differential effects on ERK3 protein stability in a cell type dependent manner. Whilst in primary cells, LPS stimulation induced rapid ubiquitination and proteasomal degradation of ERK3, LPS seems to stabilize levels of ERK3 by blocking its proteasomal degradation in HT-29 cells. However, the IL-8 levels correlate to the expression of ERK3 irrespective of the cell types. Blocking of the proteasomal degradation led to an accumulation of ERK3 protein and consequently rescued IL-8 levels regardless of the inhibition of MEK1/2-ERK1/2 pathway. Most importantly, loss of ERK3 levels led to a strong reduction in IL-8 levels despite the inhibition of the classical MAPK cascades or activation of NF-κB. In addition, MK5 and ERK4 exhibit opposing effects on ERK3 levels. While the well-studied ERK1/2, p38, JNK and NF-κB pathways are reported as the main regulating pathways controlling IL-8 expression, this study unveiled a obligatory and yet synergistic role for ERK3 in the regulation of epithelial secretome, including IL-8. The study further demonstrated that the secretome of ERK3 depleted cells failed to promote leukocyte chemotaxis both in vitro and in vivo, suggesting a critical role for this atypical MAPK in the maintenance of epithelial secretome. ERK3 has been shown to be required for the maintenance of epithelial architecture and some of the observations made here may possibly contribute to this phenotype. Further, as IL-8 has been shown to play a pivotal role in tumourigenesis and metastasis, attempts could be made to target ERK3 in these settings. Taken together, the body of the work presented here unveils a critical role for this atypical MAPK in the regulation of epithelial secretome and leukocyte chemotaxis.» weiterlesen» einklappen

Autoren

Klassifikation

DDC Sachgruppe:
Biowissenschaften, Biologie