Toward a better understanding of human polarized epithelial biology: Mucin 4 in endometrium and polarity complexes in salivary epithelium
Chapela, Patricia Jensen
Carson, Daniel D
Doctor of Philosophy
The epithelium is one of four major tissues in the human body. It covers every surface and cavity. Epithelial cells have an intracellular organization they use to differentiate the top, or apical surface, of the cell from the basal surface at the bottom. The cell localizes transmembrane proteins to specific regions for particular functions. Loss of this polarization cause cells to function abnormally as can occur in cancer. Therefore, understanding the basic function and organization of epithelial cells will aid in many areas of human health from diagnosis of disease to tissue regeneration. This work focuses on two separate projects; mucin expression in multiple cell lines originating from human female reproductive tissues, and cellular apicobasal polarity in salivary epithelial cells. For the first focus, cells localize mucins to their apical surface to protect and lubricate the external cell surface. Over the course of my studies in multiple epithelial cell lines, I found mucin 4 (MUC4) stead-state levels of transcripts and proteins increase when cells are exposed to the pro-inflammatory cytokines, interferon and tumor necrosis factor . In healthy endometrium, MUC4 was not present at levels comparable to mucin 1 or mucin 16; however, it was detectable in endometrial cancer. In light of the response to pro-inflammatory cytokines, it is not surprising to have higher quantities of MUC4 in endometrial tumor tissue. Furthermore, in cancer, cells tend to lose their polarity allowing proteins to interact that are typically separated. In endometrial cancer, this loss of polarity allows MUC4 to stabilize a growth receptor, ERBB2, normally relegated to the basal membrane. The second project involved a close examination of salivary epithelial tissue revealing ductal cells maintain their polarity with different proteins than the highly secretory acinar cells. Specifically, ductal cells have higher levels of a key polarity protein, SCRIB, and the mRNA of INADL, a component of the apical polarity complex. However, while these proteins may not be abundant in acinar cells, acinar epithelial cells do establish and maintain polarity. Acinar cells localize tight junction proteins in different structures than ductal cells due in part to their different functions. This project focused on identifying the difference between these two cell types in the salivary gland and the culture conditions necessary to polarize cultured primary cells. The ability to differentiate cultured cells into both epithelial cell types is vital to the generation of a functional salivary gland. These projects encompassed two different questions involving the phenotypes of different epithelial cells in different tissues. From the first project, observed responses to cytokines suggested a potential role for MUC4 in inflammatory conditions. In the second project, the ultimate goal of developing an autologous salivary gland for implantation in xerostomia patients requires determining the growth factors and basement membrane cues fundamental to developing a properly organized and functioning salivary gland. The complete work detailed here gives insight into the function of epithelial cells in these different contexts.