Statin, a 57 kilodalton (kDa) nuclear protein, is characteristically found in nonproliferating cells in culture as well as nondividing cells of a wide range of highly differentiated tissues. Moreover, cells in culture that are statin positive lose this statin expression when re-entering the cell-cycle traverse. In this work, statin expression was investigated in the parotid gland of untreated rats and those treated with isoproterenol (IPR), a proliferation-inducing catecholamine. Indirect immunofluorescence microscopy revealed specific nuclear staining with anti-statin monoclonal antibody (S-44) in the acinar and ducts cells of the untreated rats but significantly reduced in those induced with isoproterenol. To characterize the protein recognized by S-44, protein extracts from both tissues were immunoblotted and incubated with S-44. The antibody reacted specifically with a 48 kDa protein in the extract of the parotid glands from untreated rats while no reaction was detected in that of the proliferation-induced ones. These observations along with the result that a statin-like (S1) transcript is downregulated by isoproterenol in the parotid glands further support the notion that the disappearance of statin-related expression is associated with the IPR-induced proliferation in the rat parotid glands. The discrepancy between the apparent molecular mass of the protein identified by S-44 in nonproliferating parotid cells and that of statin originally found in fibroblasts, suggests that either a modified form of statin may be present in the parotid gland, or this 48 kDa protein may be a member of the nonproliferative statin-like family.
Phorbol ester stimulates amylase secretion from rat parotid cells
