Surrounding virtually every mammalian organ is a specialized form of extracellular matrix (ECM) known as the basement membrane. In the mouse submandibular salivary gland (SMG), a commonly used model for tissue development, the basement membrane (BM), underlying the outermost epithelial cells, is critical for tissue organization and function. We have recently shown that the organization and expression of BM proteins surrounding the SMG is controlled by PAR-1b, a widely studied polarity protein. Decreased expression or misassembly of the basement membrane has been shown to significantly disrupt the polarization of the adjacent epithelial cells. Disruption of the basement membrane has also been seen in diseases such as Sj?gren's syndrome. Sj?gren's syndrome is an autoimmune disease that affects the exocrine glands, including the salivary glands and the lacrimal glands, decreasing secretory products (saliva and tears) and causing significant decreases in the patient's quality of life. In the salivary gland, directional secretion of salivar products relies heavily on coordinated cellular polarity, which we have previously shown to be dependent on the basement membrane. We have also shown that providing epithelial cells with an artificial matrix coated with the basement membrane protein laminin-111 also enhances cellular polarity. Cellular polarity is also dependent upon cell surface receptors such as integrin and dystroglycan that make direct contacts with the BM and frequently relay outside-in signals. I hypothesize that PAR-1b regulates the localization of cell surface receptors to the basal cell surface, which in turn regulates the assembly of laminin-111 in the basement membrane. Further, I hypothesize that in Sj?gren's syndrome, disruption of cellular polarity may lead to disruption of the basement membrane. The main goals of this research are: (1) to determine whether the localization of integrins ?3, ?6, and ?1 and dystroglycan is under the control of PAR-1b kinase activity, (2) to determine whether integrin ?3, ?6, and ?1 and/or dystroglycan regulate the assembly of laminin- 111 in the basement membrane and therefore the cellular polarity of the salivary epithelial cells, and (3) to determine whether there is a change in this proposed polarity mechanism associated with degraded the basement membrane in human and mouse salivary glands affected by Sj?gren's syndrome.
In this project, I will investigate the function of PAR-1b in regulating the placement of basement membrane and integrins, basement membrane receptors, in developing salivary glands. Par-1b is a protein required for establishment of polarity of cells n the assembly of the basement membrane, which functions in development to establish tissue shape and cell function. I will also use a novel multiplexed immunohistochemistry technique, developed by our collaborators at GE Global Research, to determine if there are changes in the localization of Par-1b and basement membrane proteins in a mouse model of Sj?gren's Syndrome and in human patients that correlate with disease.