7 research outputs found
Munc18b is an essential gene in mice whose expression is limiting for secretion by airway epithelial and mast cells
Airway mucin secretion and MC (mast cell) degranulation must
be tightly controlled for homoeostasis of the lungs and immune
system respectively. We found the exocytic protein Munc18b
to be highly expressed in mouse airway epithelial cells and
MCs, and localized to the apical pole of airway secretory cells.
To address its functions, we created a mouse with a severely
hypomorphic Munc18b allele such that protein expression in
heterozygotes was reduced by∼50%. Homozygous mutant mice
were not viable, but heterozygotes showed a ∼50% reduction
in stimulated release of mucin from epithelial cells and granule
contents from MCs. The defect in MCs affected only regulated
secretion and not constitutive or transporter-mediated secretion.
The severity of passive cutaneous anaphylaxiswas also reduced by
∼50%, showing that reduction of Munc18b expression results
in an attenuation of physiological responses dependent on MC
degranulation. The Munc18b promoter is controlled by INR
(initiator), Sp1 (specificity protein 1), Ets, CRE (cAMP-response
element), GRE (glucocorticoid-response element), GATA and
E-box elements in airway epithelial cells; however, protein levels
did not change during mucous metaplasia induced by allergic
inflammation. Taken together, the results of the present study
identifyMunc18b as an essential gene that is a limiting component
of the exocytic machinery of epithelial cells and MCs
SNAP23 Is Selectively Expressed in Airway Secretory Cells and Mediates Baseline and Stimulated Mucin Secretion
Airway mucin secretion is important pathophysiologically and as a model of polarized epithelial regulated exocytosis. We find the trafficking protein, SNAP23 (23-kDa paralogue of synaptosome-associated protein of 25 kDa), selectively expressed in secretory cells compared with ciliated and basal cells of airway epithelium by immunohistochemistry and FACS, suggesting that SNAP23 functions in regulated but not constitutive epithelial secretion. Heterozygous SNAP23 deletant mutant mice show spontaneous accumulation of intracellular mucin, indicating a defect in baseline secretion. However mucins are released from perfused tracheas of mutant and wild-type (WT) mice at the same rate, suggesting that increased intracellular stores balance reduced release efficiency to yield a fully compensated baseline steady state. In contrast, acute stimulated release of intracellular mucin from mutant mice is impaired whether measured by a static imaging assay 5 min after exposure to the secretagogue ATP or by kinetic analysis of mucins released from perfused tracheas during the first 10 min of ATP exposure. Together, these data indicate that increased intracellular stores cannot fully compensate for the defect in release efficiency during intense stimulation. The lungs of mutant mice develop normally and clear bacteria and instilled polystyrene beads comparable to WT mice, consistent with these functions depending on baseline secretion that is fully compensated
SNAP23 is selectively expressed in airway secretory cells and mediates baseline and stimulated mucin secretion
Airway mucin secretion is important pathophysiologically and as a model of polarized epithelial regulated exocytosis. We find the trafficking protein, SNAP23 (23-kDa paralogue of synaptosome-associated protein of 25Â kDa), selectively expressed in secretory cells compared with ciliated and basal cells of airway epithelium by immunohistochemistry and FACS, suggesting that SNAP23 functions in regulated but not constitutive epithelial secretion. Heterozygous SNAP23 deletant mutant mice show spontaneous accumulation of intracellular mucin, indicating a defect in baseline secretion. However mucins are released from perfused tracheas of mutant and wild-type (WT) mice at the same rate, suggesting that increased intracellular stores balance reduced release efficiency to yield a fully compensated baseline steady state. In contrast, acute stimulated release of intracellular mucin from mutant mice is impaired whether measured by a static imaging assay 5Â min after exposure to the secretagogue ATP or by kinetic analysis of mucins released from perfused tracheas during the first 10Â min of ATP exposure. Together, these data indicate that increased intracellular stores cannot fully compensate for the defect in release efficiency during intense stimulation. The lungs of mutant mice develop normally and clear bacteria and instilled polystyrene beads comparable to WT mice, consistent with these functions depending on baseline secretion that is fully compensated
Munc18b is an essential gene in mice whose expression is limiting for secretion by airway epithelial and mast cells
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SNAP23 is selectively expressed in airway secretory cells and mediates baseline and stimulated mucin secretion.
Airway mucin secretion is important pathophysiologically and as a model of polarized epithelial regulated exocytosis. We find the trafficking protein, SNAP23 (23-kDa paralogue of synaptosome-associated protein of 25 kDa), selectively expressed in secretory cells compared with ciliated and basal cells of airway epithelium by immunohistochemistry and FACS, suggesting that SNAP23 functions in regulated but not constitutive epithelial secretion. Heterozygous SNAP23 deletant mutant mice show spontaneous accumulation of intracellular mucin, indicating a defect in baseline secretion. However mucins are released from perfused tracheas of mutant and wild-type (WT) mice at the same rate, suggesting that increased intracellular stores balance reduced release efficiency to yield a fully compensated baseline steady state. In contrast, acute stimulated release of intracellular mucin from mutant mice is impaired whether measured by a static imaging assay 5 min after exposure to the secretagogue ATP or by kinetic analysis of mucins released from perfused tracheas during the first 10 min of ATP exposure. Together, these data indicate that increased intracellular stores cannot fully compensate for the defect in release efficiency during intense stimulation. The lungs of mutant mice develop normally and clear bacteria and instilled polystyrene beads comparable to WT mice, consistent with these functions depending on baseline secretion that is fully compensated
SNAP23 is selectively expressed in airway secretory cells and mediates baseline and stimulated mucin secretion.
Airway mucin secretion is important pathophysiologically and as a model of polarized epithelial regulated exocytosis. We find the trafficking protein, SNAP23 (23-kDa paralogue of synaptosome-associated protein of 25 kDa), selectively expressed in secretory cells compared with ciliated and basal cells of airway epithelium by immunohistochemistry and FACS, suggesting that SNAP23 functions in regulated but not constitutive epithelial secretion. Heterozygous SNAP23 deletant mutant mice show spontaneous accumulation of intracellular mucin, indicating a defect in baseline secretion. However mucins are released from perfused tracheas of mutant and wild-type (WT) mice at the same rate, suggesting that increased intracellular stores balance reduced release efficiency to yield a fully compensated baseline steady state. In contrast, acute stimulated release of intracellular mucin from mutant mice is impaired whether measured by a static imaging assay 5 min after exposure to the secretagogue ATP or by kinetic analysis of mucins released from perfused tracheas during the first 10 min of ATP exposure. Together, these data indicate that increased intracellular stores cannot fully compensate for the defect in release efficiency during intense stimulation. The lungs of mutant mice develop normally and clear bacteria and instilled polystyrene beads comparable to WT mice, consistent with these functions depending on baseline secretion that is fully compensated