The functional role of SIK2 in regulating large dense core vesicles (LDCVs) secretion
Date Issued
2011
Date
2011
Author(s)
Kao, Chung-Ju
Abstract
Salivary glands are an important secretory tissue of the oral cavity. From Immunohistochemical staining, we found that SIK2, a member of the AMPK family proteins, is highly expressed in salivary glands. The Ser587 residue of SIK2 has been identified as a putative phosphorylation site of PKA, which is a principal modulator in the regulation of secretion. Here we demonstrate that the context sequence around Ser587 residue of SIK2 is highly conserved among veterbrates, and identify PKAβ as the kinase that physically associates and phosphorylates SIK2 at S587 in vivo and in vitro. This phosphorylation occurs not only in the salivary glands but also in various Large dense core vesicle (LDCV)-secreting glands. Using the LDCV-mediated secretion of insulin model of β islet cells, we found that SIK2-S587 is rapidly phosphorylated upon glucose stimulation, and that this phosphorylation strongly correlates with PKA activation under physiological conditions. In Rinm5F insulinoma cells, SIK2-pS587 and PKAβ colocalize to insulin-containing LDCVs, while TEM observations indicate that SIK2-S587 phosphorylation can occurs as early as in reserve pool insulin vesicles. Our kinetics studies indicate that massive translocation of SIK2-pS587 containing insulin vesicles occurs upon glucose stimulation as observed under Total Internal Reflection Fluorescence Microscopy (TIRF). Taken together, our data suggest an important role for SIK2 in LDCV secretion, and that SIK2 may crosstalk with PKA to regulate insulin vesicle translocation in β islet cells.
Subjects
secretion
β cells
insulin vesicles
Type
thesis
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