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Regulation of airway goblet cell mucin secretion by tyrosine phosphorylation signaling pathways

¹Cystic Fibrosis/Pulmonary Research and Treatment Center, and ²Department of Cell and Molecular Physiology, University of North Carolina, Chapel Hill, North Carolina

Submitted 14 April 2007 ; accepted in final form 27 June 2007

Mucus hyperproduction in pulmonary obstructive diseases results from increased goblet cell numbers and possibly increased cellular mucin synthesis, occurring in response to inflammatory mediators acting via receptor tyrosine kinases (RYK) and tyrosine phosphorylation (Y-Pi) signaling pathways. Yet, increased mucin synthesis does not lead necessarily to increased secretion, as mucins are stored in secretory granules and secreted in response to extracellular signals, commonly assumed to be mediated by G protein-coupled receptors (GPCRs). We asked whether activation 1) of Y-Pi signaling pathways, in principal, and 2) of the novel PKC isoform, nPKC, by Y-Pi, specifically, might lead to regulated mucin secretion. nPKC in SPOC1 cells was tyrosine phosphorylated by exposure to purinergic agonist (ATPS) or PMA, actions that were blocked by the Src kinase inhibitor, PP1. Mucin secretion, however, was not affected by PP1. Hence, activation of nPKC by Y-Pi is unlikely to participate in GPCR-related mucin secretion. Mucin secretion from both SPOC1 and normal human bronchial epithelial (NHBE) cells was stimulated by generalized protein Y-Pi induced by the tyrosine phosphatase inhibitor, pervanadate (PV). PV-induced SPOC1 cell mucin secretion was not affected by inhibition of Src kinases (genistein or PP1), or of PI3 kinase (LY-294002). MAP kinase pathway inhibitors, RAF1 kinase inhibitor-I and U0126 (MEK), inhibited SPOC1 cell PV-induced secretion by 50%. Significantly, the phospholipase C (PLC) inhibitor, U-73122, essentially abolished PV- and ATPS-induced mucin secretion from both SPOC1 and NHBE cells. Hence, PLC signaling may play a key role in regulated mucin secretion, whether the event is initiated by mediators interacting with GPCRs or RYKs.

lung; mucus; exocytosis; PKC; purinergic signaling

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