REGULATION OF ACINAR CELL PROLIFERATION

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Chronic injections of the beta-adrenergic agonist, isoproterenol, produce in addition to cell hypertrophy and hyperplasia, biochemical alterations in protein synthesis in the rat and mouse parotid gland. Among the biochemical changes is an increase in specific activity and topography for an enzyme normally thought of as a Golgi membrane marker enzyme 4beta- galactosyltransferase (Gal Tase). A similar change in enzyme activity and localization is observed with the introduction of dietary and hormonal changes that result in an increased functional gland activity and resulting hyperplasia. The importance of the up-regulation and surface localization of Gal Tase became apparent in experiments in which agents that interact with this enzyme were shown to severely inhibit parotid gland hypertrophy and hyperplasia in vivo or in vitro. A cDNA clone has been isolated which specifically modulates the cell surface appearance of Gal Tase and therefore acinar cell growth. Sequence analysis of a partial cDNA indicated homology to a class of enzymes involved in cell division. The clone designated GTA (Gal Tase activator) is a Ca+2/calmodulin dependent serine protein kinase which is induced in parotid cells in response to isoproterenol. The substrate of the kinase Golgi localized Gal Tase, which upon phosphorylation, is targeted to the plasma membrane. Numerous reports have shown that alteration of cell surface Gal Tase activity might be involved in cell adhesion, differentiation and tumorogenesis. We therefore believe that studies of the regulation of the GTA gene are crucial to understanding growth control of parotid and other tissues regulated by surface Gal Tase. To accomplish this, the GTA cDNA will be used to isolate chromosomal sequences which will be analyzed for organization of regulatory sequences as well as intron and exon structure. The GTA cDNA will allow us to examine at the molecular level, the effects that gene expression and cell surface localization of Gal Tase have on acinar cell growth in vivo and in vitro. The GTA protein will be isolated and biochemically analyzed; using the purified protein for antibody production and immunohistological studies. Finally, we will continue to investigate the sequence of intracellular events involved in the signal transduction from beta-agonist to the nucleus causing expression of GTA, and the action of Gal Tase in the plasma membrane in perpetuating the signal for acinar cell proliferation. These findings will ultimately be used to evaluate the contribution of GTA expression and galactosyltransferase-mediated cell proliferation in human pathologies of the oral cavity, and in particular, disorders of the salivary glands involving tissue hypertrophy and hyperplasia.