DOI
https://doi.org/10.25772/4JHN-WG10
Defense Date
2014
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Biochemistry
First Advisor
Tomasz Kordula
Abstract
YKL-40 is a secreted glycoprotein, which is a shared biomarker of chronic inflammation and oncogenic transformation. Indeed, YKL-40 expression is up-regulated in many diseases including multiple sclerosis, Alzheimer disease, viral encephalitis, HIV-associated dementia, brain infarction, and traumatic brain injury. YKL-40 is also expressed by several solid tumors, such as osteosarcoma, ovarian carcinoma and glioblastoma multiforme (GBM). It promotes the migration and invasion of astrocytes as well as GBM cells. Serum YKL-40 levels have been shown to directly correlate with tumor grade and potentially tumor burden in GBM. In contrast to the numerous reports documenting elevated expression of YKL-40, relatively little is known about inflammatory mediators and specific molecular mechanisms that control its expression. For my PhD project, I decided to elucidate the mechanism regulating YKL-40 expression in inflammation and to understand how YKL-40 mediates the migration and invasion of GBM cells in vivo. As per my first project, I found that YKL-40 expression is up-regulated in many inflammatory models such as irritant induced inflammation (turpentine), EAE (experimental autoimmune encephalomyelitis), irradiation induced brain inflammation and in the HIV-TAT overexpression model. YKL-40 expression is also up regulated in oligodendroglioma patient samples. We show that YKL-40 expression is activated by major pro-inflammatory cytokines including IL-1, IL-6, and OSM in astrocytes, and that the activation of YKL-40 expression by cytokines depends on the STAT and NF-κB regulatory elements located within the YKL-40 promoter. Additionally, we discovered that STAT3 is a major regulator of YKL-40 expression in response to the IL-6 family cytokines, including OSM. Indeed, both depletion of STAT3 expression or overexpression of dominant-negative STAT3 abolishes activation of YKL-40 expression. In contrast, although IL-1 activates NF-κB (p65/p50) in astrocytes, IL-1-induced YKL-40 expression is p65/p50 independent, and instead regulated by the RelB/p50 complexes. Interestingly, OSM promotes formation of p50/RelB complexes. In conclusion, we found that YKL-40 is up regulated by major pro-inflammatory cytokines during inflammation associated with various disease models. Thus, we uncovered the regulatory mechanism that governs the expression of YKL-40 during sterile inflammation. Next, I studied the role of YKL-40 in GBM in vivo. The major obstacle for treatment of GBM is the unique ability of GBM cells to diffusely infiltrate healthy brain tissue. GBM tumors express high levels of YKL-40, and we showed that administration of YKL-40 increases migration and invasion of U1242 cells in vitro. We used the U1242 cell line for our studies, due to its unique ability to form infiltrative tumors, which reflects the real brain pathology in GBM. Additionally, knock-down of YKL-40 suppresses the migration and invasion of GBM cells in vitro. To study this phenomenon in vivo, we utilized an inducible lentiviral vector containing shRNA to YKL-40. We generated stable GBM cells containing this shYKL-40 vector and used them in a mouse xenograft model for glioma to evaluate the effect of YKL-40 in invasion and migration of GBM cells. RelB expression is increased in GBM patients, and it is associated with up-regulation of a distinct subset of gene. Here we show that RelB expression is increased during inflammation in response to IL-1, where it can enhance the expression of YKL-40, which can modulate the inflammatory response. Thus, we found that YKL-40 is up regulated by major inflammatory cytokines during inflammation associated with various diseases. In addition, YKL-40 secreted by brain cells other than GBM cells may have an effect on invasion of GBM cells in vivo.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-15-2014