Switching of cargo sorting from the constitutive to regulated secretory pathway by the addition of cystatin D sequence in salivary acinar cells.

We examined the transport of HaloTag proteins fused with full-length cystatin D (fCst5-Halo) or only its signal peptide (ssCst5-Halo) in parotid acinar cells. Although both fusion proteins were observed to be colocalized with amylase in the secretory granules, the coefficients for overlapping and correlation of fCst5-Halo with amylase were higher than those of ssCst5-Halo. The secretion of both the proteins was enhanced by the addition of the β-adrenergic receptor agonist isoproterenol, as well as endogenous amylase. In contrast, unstimulated secretion of ssCst5-Halo without isoproterenol was significantly higher than that of fCst5-Halo and amylase. Simulation analysis using a mathematical model revealed that a large proportion of ssCst5-Halo was secreted through the constitutive pathway, while fCst5-Halo was transported into the secretory granules more efficiently. Precipitation of fCst5-Halo from cell lysates was increased at a low pH, which may mimic the milieu of the trans-Golgi network. These data suggest that the addition of a full-length sequence of cystatin D facilitates efficient selective transport into the regulated pathway by aggregation at low pH in the trans-Golgi network. PMID: 32538138 [PubMed - as supplied by publisher]
Source: Am J Physiol Gastroi... - Category: Gastroenterology Authors: Tags: Am J Physiol Gastrointest Liver Physiol Source Type: research