Mucus hypersecretion in the patients with airway diseases represents poor prognosis as well as discomfort. However, there is no known therapy for its effective control. One important component of mucus is mucin, a glycosylated protein, which endows mucus with viscosity. We studied whether a proteinase has a role in mucin secretion and if so, which.

(1) Inhibition of mucin secretion

Group-specific proteinase inhibitors were tested to evaluate whether a proteinase belonging to a group of proteinases plays a role in mucin secretion. Phenylmethylsulfonyl fluoride(PMSF, a serine proteinase inhibitor), E-64(a cysteine proteinase inhibitor), Pepstatin(an aspartic proteinase inhibitor) and 1, 10-Phenanthroline(a metalloproteinase inhibitor) were treated into the Calu-3 cell line for 24 hours. The enzyme linked immunoabsorbant assay(ELISA) for MUC5AC was performed to evaluate the amount of mucin secretion and to compare with a control.

(2) Stimulation of mucin secretion

Matrix metalloproteinase-9(MMP-9), MMP-12 and TACE(TNF-alpha converting enzyme), which are known to be related with airway diseases, were used to be treated into Calu-3 for 24 hours. ELISA for MUC5AC was performed to evaluate the amount of mucin secretion and to compare with the controls.

(1) PMSF(10^-4M), E-64(10^-4M), Pepstatin(10^-6M) and 1, 10-Phenanthroline(10^-4M) reduced the MUC5AC secretion by 1 ± 4.9%(mean ± standard deviation; P=1.0 compared with the control), -6 ± 3.9%(P=0.34), -13 ± 9.7%(P=0.34) and 41 ± 8.2%(P=0.03), respectively.

(2) The amounts of MUC5AC secretion stimulated by MMP-9(250ng/ml), MMP-12(100ng/ml) and TACE(200ng/ml) were 103 ± 6%(P=0.39), 102 ± 8%(P=1.0) and 107 ± 13%(P=0.39), respectively, compared with the controls.

Metalloproteinase(s) is (are) suggested to play a role in mucin secretion. It appears that metalloproteinases, other than MMP-9, MMP-12 or TACE, affect the mucin secretion in this in vitro model.