Expression and localization of calpain 3 in the submandibular gland of mice

• Calpain 3, the muscle-type calpain, occurs in the submandibular gland (SMG) of mice.
• Calpain 3 is expressed preferentially in the male SMG with androgen dependence.
• Calpain 3 is localized in the cytosolic areas of granular convoluted tubule cells.

ObjectivesCalpains comprise a family of intracellular Ca2+-dependent cysteine proteases and are considered to play roles in various physiological phenomena with limited proteolytic activities against specific substrates. We herein revealed the expression and localization of calpain 3, the muscle-type calpain, in the submandibular gland (SMG) of mice.DesignThe expression of the mRNA for conventional, ubiquitous calpains 1 and 2 and skeletal muscle-specific calpain 3 was examined in the major salivary glands of mice using RT-PCR, and the expression and localization of calpain 3 protein was examined in the SMG of mice using immunohistochemistry and Western blotting.ResultsThe large catalytic subunits of calpains 1 and 2 and the small regulatory subunit common to calpains 1 and 2 were weakly expressed in the parotid gland, sublingual gland, and SMG at similar levels in males and females. In contrast, the single large catalytic subunit of calpain 3 was expressed predominantly in the SMG at markedly higher levels in males than in females and in a manner dependent on androgens. Immunoreactivity for calpain 3 was mainly localized in cells of the granular convoluted tubules (GCT) that developed preferentially in the male SMG. In GCT cells, calpain 3 immunoreactivity was localized predominantly in the cytosolic region and was absent in the secretory granules.ConclusionsThese results revealed that the GCT is the primary site of production of calpain 3 in the mouse SMG.