Date of Award
Doctor of Philosophy
Synemin intermediate filament (IF) protein is unlike other members of the IF protein family due to its size, structure, and pattern of expression. Synemin polymerizes with Type III IF proteins and is found in a wide variety of tissues, most of which are mesenchymal in origin. However, the presence of synemin in tumors of mesenchymal origin is unknown. Because IF proteins are widely used to identify tumor types as well as to predict the clinical outcomes of tumors, we have evaluated by immunoperoxidase the presence of synemin in fifty-three tumors of mesenchymal origin (sarcomas). The majority (62%) of the sarcomas examined exhibited 1.0% to 10.0% cytoplasmic positivity for synemin. There was also a significant number of cases (21%) with particularly intense (>30.0%) synemin staining, including all five gastrointestinal stromal cell tumors (GIST). The presence of synemin in GIST was further evaluated by immunoperoxidase in fifty-four cases of GIST and was compared to that of CD34, one of the markers currently used to identify GIST tumors. The results show that synemin is a more sensitive marker than CD34 in identifying GIST. Additionally, synemin was found in interstitial cells of Cajal (ICC), the pacemaker cells which regulate peristalsis in the gastrointestinal tract and which give rise to GIST. Early studies have shown that synemin is present in amphibian and avian nucleated red blood cells. This prompted us to examine by immunofluorescence the expression of synemin in erythroblasts, which are the nucleated precursors of red blood cells and are located in the bone marrow. Our results suggest that synemin may be present in a subpopulation of erythroblasts. They also demonstrate that, unexpectedly, synemin is consistently present in platelets and in their precursors, the megakaryocytes, suggesting that synemin may play a role in platelet shedding by megakaryocytes. Finally, synemin is present in neurons of the peripheral nervous system (PNS). Since IF proteins other than synemin have been shown to be key regulators of axonal caliber, we examined the role of synemin in N2a neuroblastoma cells, which are derived from PNS neurons. We used CRISPr/Cas9 to knock down synemin in N2a neuroblastoma cells. Our results demonstrate that synemin is a positive regulator of N2a cell proliferation, but that it does not play a role in the extension of neurites by these cells. However, synemin was involved in determining the size of the cell body of N2a cells.Altogether, our results suggest that synemin is more widely expressed than previously thought, which raises questions as to its role(s) in the different cell types in which it is expressed. Our results with N2a cells also suggest that in tumor cells, the primary role of synemin is that of a positive regulator of cell proliferation.
Dissertation or thesis originally submitted to ProQuest
Criswell, Sheila, "Presence and Function of Intermediate Filament Protein Synemin in Proliferative Tissues" (2020). Electronic Theses and Dissertations. 2892.