Bronchial tissue kallikrein activity is regulated by hyaluronic acid binding

Tissue kallikrein (TK) is secreted by serous cells of tracheobronchial subm ucosal glands and plays a role in allergic airway responses. To better unde rstand the regulation of TK, we used primary cultures of submucosal gland c ells that release TK upon stimulation. Media From cultures stimulated with chymase (10(-7) M) showed increased TK activity (0.50 +/- 0.22 mU/ml mean /- standard error) in comparison with the control group (0.08 +/- 0.02 mU/m l). The increased TK activity was significantly correlated with in creases in the levels of the serous cell marker, secretory leukoprotease inhibitor. Anion exchange chromatography of the conditioned culture media showed that TK activity eluted as a broad peak between 1.6 and 1.8 M NaCl, unlike the reported elution (0.3 to 0.6 M NaCl) of kallikreins from other tissues, sug gesting that secreted bronchial TK was bound to a negatively charged molecu le. Hyaluronidase digestion increased TK activity in both pre- and post-chy mase-stimulated culture media, whereas no such change was seen after sample s were digested with heparinase or chondroitinase ABC. Further, after hyalu ronidase digestion of media, TK eluted from an anion exchange column betwee n 0.3 and 0.6 M NaCl. Enzymatic detection of TK after nondenaturing gel ele ctrophoresis showed that hyaluronidase digestion also reduced the electroph oretic heterogeneity of TK to a single band, whereas adding back hyaluronic acid (HA) to hyaluronidase-digested samples restored the original heteroge neity. Finally, TK activity bound to HA-Seph arose and could be eluted with HA. These studies show that primary cultures of ovine submucosal gland cel ls secrete TK in a regulated fashion, and that secreted TK binds to HA. Thi s binding reduces TK enzymatic activity; therefore, factors that affect HA turnover could modify the TK activity in the airway lumen. These events cou ld be important in the regulation of kinin-mediated airway inflammation. Fo rteza, R., I. Lauredo, W. M. Abraham, and G. E. Conner. 1999. Bronchial tis sue kallikrein activity is regulated by hyaluronic acid binding.