Author ORCID Identifier
http://www.orcid.org/0000-0003-1503-5671
Date of Graduation
5-2017
Document Type
Dissertation (PhD)
Program Affiliation
Cancer Biology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Raghu Kalluri, MD, PhD
Committee Member
Jian Hu, PhD
Committee Member
Honami Naora, PhD
Committee Member
Shao-Cong Sun, PhD
Committee Member
Kwong-Kwok Wong, PhD
Abstract
The initiation, progression, and metastasis of tumors involve not only cancer cells, but also the tumor microenvironment, which consists of immune or inflammatory cells, fibroblasts, endothelial cells, and extracellular matrix components (ECM). Fibroblasts are ubiquitous stromal cells that can influence other neighboring cell types through the secretion of chemokines, cytokines, ECM, ECM remodeling enzymes, and other metabolites. Myofibroblasts are a distinct subtype of fibroblasts characterized by expression α-smooth muscle actin (αSMA). These cells are a dominant component of the microenvironment, and a FSP1 and FAP could be a different clone of fibroblasts. Myofibroblasts also have been known to contribute to cancer progression and metastasis in multiple cancer types including breast and pancreas cancer, both of which are associated with extensive desmoplasia. However, the role of αSMA+ myofibroblasts in the context of colorectal cancer has remained largely descriptive and functionally unknown. The studies outlined in this project explored the functional contribution of αSMA+ myofibroblasts in the disease progression of colorectal cancer. To address this, we used the spontaneous colorectal cancer model, which consists of 6 alleles: Villin-Cre-ERT2; APCflox/flox; p53flox/flox; tetO-LSL-KrasG12D; Rosa26-LSL-Luc; Rosa26-LSL-rtTA- eGFP. These mice were bred with αSMA-TK and αSMA-RFP transgenic mice for selective targeting and monitoring of myofibroblasts in the tumor microenvironment in these eight allelic transgenic mice.
Mice with αSMA+ myofibroblast-depleted tumors exhibited hind limb paresis, which likely contributed to their decreased overall survival. Intraluminal tumor burden appeared reduced in myofibroblast-depleted tumors; however, the tumors were depressed resulting in more invasion to both the vascular and lymphatic vessels. The depletion of myofibroblast surprising resulted in increased deposition of ECM and generation of an immunosuppressive microenvironment with the accumulation of CD4+ Foxp3+ Treg. Furthermore, we discovered that the population of cancer stem cells expressing Lgr5 and Dclk1 was increased in αSMA+ myofibroblast-depleted tumors. In conclusion, our study reveals the unknown functional role of myofibroblasts in regulating T cell-meditated anti- tumor immunity and stemness features in colon cancer cells.
Keywords
Myofibroblasts, Cancer stem cells, Regulatory T cells, Colorectal cancer