The Complex of Ciliary Neurotrophic Factor-Ciliary Neurotrophic Factor Receptor α Up-Regulates Connexin43 and Intercellular Coupling in Astrocytes via the Janus Tyrosine Kinase/Signal Transducer and Activator of Transcription Pathway

Cytokines regulate numerous cell processes, including connexin expression and gap junctional coupling. In this study, we examined the effect of ciliary neurotrophic factor (CNTF) on connexin43 (Cx43) expression and intercellular coupling in astrocytes. Murine cortical astrocytes matured in vitro were treated with CNTF (20 ng/ml), soluble ciliary neurotrophic factor receptor α (CNTFRα) (200 ng/ml), or CNTF-CNTFRα. Although CNTF and CNTFRα alone had no effect on Cx43 expression, the heterodimer CNTF-CNTFRα significantly increased both Cx43 mRNA and protein levels. Cx43 immunostaining correlated with increased intercellular coupling as determined by dye transfer analysis. By using the pharmacological inhibitor α-cyano-(3,4-dihydroxy)-N-benzylcinnamide (AG490), the increase in Cx43 was found to be dependent on the Janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT) pathway. Immunocytochemical analysis revealed that CNTF-CNTFRα treatment produced nuclear localization of phosphorylated STAT3, whereas CNTF treatment alone did not. Transient transfection of constructs containing various sequences of the Cx43 promoter tagged to a LacZ reporter into ROS 17/2.8 cells confirmed that the promoter region between -838 to -1693 was deemed necessary for CNTF-CNTFRα to induce heightened expression. CNTF-CNTFRα did not alter Cx30 mRNA levels, suggesting selectivity of CNTF-CNTFRα for connexin signaling. Together in the presence of soluble receptor, CNTF activates the JAK/STAT pathway leading to enhanced Cx43 expression and intercellular coupling

Enhanced Neurite Outgrowth in PC12 Cells Mediated by Connexin Hemichannels and ATP

Gap junctions have traditionally been described as transmembrane channels that facilitate intercellular communication via the passage of small molecules. Connexins, the basic building blocks of gap junctions, are expressed in most mammalian tissues including the developing and adult central nervous system. During brain development, connexins are temporally and spatially regulated suggesting they play an important role in the proper formation of the central nervous system. In the current study, connexins 32 and 43 were overexpressed in PC12 cells to determine whether connexins are involved in neuronal differentiation. Both connexin 32 and 43 were appropriately trafficked to the cell membrane following overexpression and resulted in the formation of functional gap junctions. Connexin overexpression was found to cause enhanced neurite outgrowth in PC12 cells treated with nerve growth factor to initiate neuritogenesis. Surprisingly, however, enhanced neurite outgrowth was found to be the consequence of functional hemichannel formation as opposed to traditional intercellular communication. Additional analysis revealed that ATP was released into the media likely through hemichannels and acted on purinergic receptors to cause enhanced neurite outgrowth. Collectively, the results of the current study suggest that connexins may play an important role in neuronal differentiation by non-traditional mechanisms