Type of Thesis
Dr. Marissa Ehringer
Dr. Alena Grabowski
Dr. Jennifer Knight
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In cancer, transforming growth factor β (TGFβ) paradoxically functions as both a tumor suppressor and tumor promoter. In early-stage disease, TGFβ suppresses tumor growth by inducing cell cycle arrest and apoptosis. In late-stage disease, TGFβ promotes tumor cell invasiveness and metastasis. Often, mutations or genomic alterations in the TGFβ pathway are responsible for shifting the balance of TGFβ from tumor suppressor to tumor promoter. In endometrial cancer (EC), TGFβ pathway mutations and genomic alterations are rare, which suggests that the loss or gain of downstream targets are involved in shifting the balance. Another molecule, CD73, has also been implicated in EC. CD73 is a cell surface 5’nucleotidase that, in normal endometrium, protects epithelial integrity by increasing membrane F-actin. However, the loss of CD73 has also been found to increase EC progression.1
Recent work has found that TGFβ increases CD73 expression in normal endometrium and in HEC-1-A cells, a model of early-stage EC. The purpose of this study was to determine if loss of CD73 in EC shifts the action of TGFβ from a tumor suppressor to a tumor promoter. F- actin immunofluorescence was used to assess epithelial differentiation in normal murine endometrium. F-actin expression was increased in both glandular and luminal epithelial cells of mice treated with TGFβ. Additionally, F-actin and CD73 mRNA expression were positively correlated. These data suggest that TGFβ is associated with increasing CD73 and differentiation in normal endometrial tissue, and thus provide further evidence that TGFβ acts as a tumor suppressor in normal endometrium.
HEC-1-A cells were used to determine if inhibiting CD73 would increase TGFβ- mediated tumor-promoting activities in early-stage EC. MTT colorimetric assays showed that inhibiting CD73 with α,β-Methylene-ADP (AoPCP) increased cell proliferation in TGFβ-treated cells. Phosphorylated SMAD2/3 and CD73 protein expression increased with TGFβ, indicating TGFβ increases CD73 through its canonical signaling pathway. Inhibiting CD73 in TGFβ-treated cells increased the protein expression of pro-metastatic transcription factor, Slug. Preliminary data also showed that inhibiting CD73 in TGFβ-treated cells decreased total F-actin. Taken together, these findings suggest that the loss of CD73 in EC shifts the action of TGFβ from tumor suppressor to tumor promoter. Future studies will focus on determining if the TGFβ- mediated increase of F-actin is via CD73. A better understanding of these and other molecular mediators of tumor progression can lead to the development of more targeted EC treatments.
Kazen, Claire, "Loss of CD73 Shifts TGF-β1 from Tumor Suppressor to Tumor Promoter in Endometrial Cancer" (2018). Undergraduate Honors Theses. 1732.