Author ORCID Identifier
https://orcid.org/0000-0001-9050-8227
Date of Graduation
12-2023
Document Type
Dissertation (PhD)
Program Affiliation
Cancer Biology
Degree Name
Doctor of Philosophy (PhD)
Advisor/Committee Chair
Ronald DePinho, M.D.
Committee Member
Scott Kopetz, M.D., Ph.D.
Committee Member
Guillermina Lozano, Ph.D.
Committee Member
Traver Hart, Ph.D.
Committee Member
Jian Hu, Ph.D.
Abstract
While colorectal cancer (CRC) patients diagnosed with localized stage disease (as defined by SEER) have a 5-year survival rate of 90%, this rate plunges to 14% for patients diagnosed with metastatic CRC. Consequently, there is an immediate imperative to elucidate the mechanisms that drive the transition to advanced CRC.
Human CRCs carrying oncogenic mutations in the KRAS oncogene, henceforth referred to as KRAS*, exhibit a 25% higher propensity for developing liver metastases. Similarly, in our CRC mouse model, engineered with an inducible Kras* transgene and conditional null alleles of Apc and Tp53 (referred to as iKAP), KRAS* has been implicated in driving cancer progression and metastasis. Mechanistically, KRAS*-driven cancer metastasis operates, in part, by activating cancer cell-intrinsic TGFβ signaling and suppressing anti-tumoral immunity through the IRF2-CXCL3 axis, which recruits myeloid-derived suppressor cells. Regrettably, emerging therapies targeting KRAS* have demonstrated limited efficacy in clinical settings. This challenge has spurred our efforts to identify and validate additional mechanisms underpinning KRAS*-driven cancer progression, with the ultimate aim of expanding the array of therapeutic targets for metastatic CRC. By utilizing the iKAP model and employing functional gene set enrichment and histological analyses of KRAS*-expressing CRC metastases, we have uncovered a robust adipogenesis signature and an abundance of lipid-rich fibroblasts and angiogenesis in the tumor microenvironment. Consequently, our co-culture experiments involving mouse embryonic fibroblasts and conditioned media from iKAP primary cell lines have induced their differentiation into a cell population displaying traits of both adipocytes and fibroblasts, aptly referred to as 'lipid-rich fibroblasts.' In the initial segment of my study, I have elucidated the molecular mechanisms through which KRAS*-expressing cancer cells drive lipo-fibrogenesis and have shed light on the tumor biological role of lipid-rich fibroblasts in facilitating KRAS*-driven CRC progression.
As only a minority of cases among both human and mouse KRAS* CRC show progression to metastatic disease, it is clear that genetic events beyond KRAS activation play a pivotal role in driving metastases. Notably, patients, irrespective of KRAS mutations, exhibit a nearly identical lymph node metastatic rate of approximately 40%. In order to explore these pro-metastasis events more effectively, I propose an integration of an inducible telomerase reverse transcriptase (LSL-Tert) into our existing iAP model, which is engineered with conditional null alleles of Apc and Tp53. This introduced modification enables us to replicate telomere-based crisis and genome instability, subsequently followed by telomerase reactivation. In prior studies employing telomerase-inducible mouse models of prostate cancer, the introduction of crisis-telomerase sequences led to the development of cancer-relevant genomic aberrations and an escalation in metastatic potential. While the inclusion of genomic instability within the iAP model may not fully replicate the intricacies of the human context, it does provide a platform for identifying gene alterations and biological transformations associated with the metastatic process. In the second phase of my research, I have introduced human-like telomere dynamics into the iAP model (referred to as iTAP) to investigate the consequences of telomere-based crisis and telomerase reactivation in driving metastasis and unraveling the underlying biological changes. These endeavors hold the potential to expedite the discovery of novel therapeutic targets for advanced CRC disease.
Keywords
KRAS, lipid-rich CAFs