ABSTRACT
Cytohesins are a family of highly homologous guanine nucleotide exchange factors (GEFs) that act on ADP-ribosylation factors (ARFs). The small ARF-GEFs are involved in integrin signaling, actin cytoskeleton remodeling, and vesicle transport. Here, we selected and applied a specific inhibitor for ARF nucleotide-binding site opener (ARNO)/cytohesin-2, an RNA aptamer that clearly discriminates between cytohesin-1 and cytohesin-2. This reagent bound to an N-terminal segment of cytohesin-2 and did not inhibit ARF-GEF function in vitro. When transfected into HeLa cells, it persisted for at least 6 h without requiring stabilization. Its effect in vivo was to down-regulate gene expression mediated through the serum-response element and knockdown mitogen-activated protein kinase activation, indicating that cytohesin-2 acts by means of mitogen-activated protein kinase signaling. We conclude that the N-terminal coiled-coil and parts of the Sec7 domain of cytohesin-2 are required for serum-mediated transcriptional activation in nonimmune cells, whereas cytohesin-1 is not. Our results indicate that intramer technology can be used not only for assigning novel biological functions to proteins or protein domains but also to prove nonredundancy of highly homologous proteins.
Subject(s)
GTPase-Activating Proteins/genetics , GTPase-Activating Proteins/metabolism , Serum Response Element/genetics , Transcriptional Activation/physiology , ADP-Ribosylation Factors/metabolism , Base Sequence , Cell Adhesion Molecules/genetics , Cell Adhesion Molecules/metabolism , GTPase-Activating Proteins/chemistry , Gene Expression , Guanine Nucleotide Exchange Factors/chemistry , HeLa Cells , Humans , MAP Kinase Signaling System/physiology , Molecular Sequence Data , Protein Structure, Tertiary , RNA/metabolism , Transcription, Genetic/physiologyABSTRACT
The clinical course of Cystic Fibrosis is characterized by recurrent pulmonary infections which ultimately lead to death by respiratory failure. The most common CF causing mutation, deltaF508-CFTR, produces an incorrectly folded protein, which accumulates within the endoplasmic reticulum. However, the molecular mechanism by which the deltaF508-CFTR protein facilitates pulmonary infection and inflammation remains unclear. Here we show that the expression of deltaF508-CFTR causes a constitutive activation of the pro-inflammatory transcription factor NF-kappaB by eliciting an ER stress reaction, the ER-overload response. This endogenous NF-kappaB activation stimulates the transcription of pro-inflammatory cytokines thereby commencing an inflammatory cascade within the CF lung.
