Date of Degree

6-2020

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biochemistry

Advisor

Olorunseun O. Ogunwobi

Committee Members

David Foster

Karen Hubbard

Moira Sauane

Jose Trevino

Keywords

c-MET, chemoresistance, microRNA-198, oxytocin receptor, pancreatic cancer

Abstract

Despite some recent advances, the detailed molecular mechanisms of pancreatic cancer (PC) are still not clearly understood, and the prognosis remains very dismal for PC patients. Consequently, there is an urgent need for a better understanding of the detailed molecular mechanisms of PC and the development of novel prognostic biomarkers and more effective treatment options.

MicroRNAs (miRNAs) are small non-coding RNAs, about 19 to 22 nucleotides in length, that inhibit translation by typically binding to 3’UTR of the target mRNA. They have recently gained much attention as key regulators in tumor initiation, progression, and chemoresistance in a variety of cancers, including PC. MicroRNA-198 (miR-198) is significantly downregulated in a variety of cancers, including PC, acting as a tumor suppressor. However, its role in PC chemoresistance is not fully understood.

Hepatocyte growth factor receptor (c-MET), a well-known proto-oncogene, is overexpressed in PC and has been implicated in PC chemoresistance and is known to lead to cell proliferation via the extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling pathway. miR-198 directly regulates c-MET in hepatocellular carcinoma (HCC) and colorectal cancer (CRC).

There is an emerging link between oxytocin (OXT), the oxytocin receptor (OXTR), and cancer. However, the role of OXT or the OXTR in PC remains unknown. OXT binds to OXTR and activates a series of downstream elements, which leads to the transient activation of ERK1/2, which promotes proliferation.

This study aimed to determine the role of miR-198 regulation of c-MET in PC chemoresistance and to investigate the role of OXT and OXTR in PC chemoresistance. We hypothesized that ERK1/2 signaling is a mediator of OXTR – dependent and miR-198/c-Met - dependent chemoresistance in PC. This hypothesis was tested using a combination of molecular and functional studies in human PC cell line models categorized in terms of their responsiveness to the current standard of care in PC, gemcitabine (Gemzar).

In this study, we have demonstrated that miR198 shows decreased expression in the human PC cell line that is more unresponsive to gemcitabine, PANC-1 than in the human PC cell line that is more responsive to gemcitabine, L3.6pl. We also observed that miR-198 regulates c-MET in the PANC-1 and L3.6pl cell lines, and specifically targets the 3’-UTR of c-MET in the PANC-1 cell line. We also found that miR-198 increases gemcitabine sensitivity in PANC-1, but not via the ERK1/2 signaling pathway.

It is also notable that OXT and OXTR are expressed in the human PC cell lines PANC-1 and L3.6pl. Inhibiting the OXTR increases gemcitabine sensitivity, but not via the ERK1/2 signaling pathway. Inhibition of OXTR also resulted in decreased ERK1/2, pERK1/2, and cyclin D1 protein expression as well as increased caspase 3 activity.

We also assessed the clinical relevance, in terms of overall survival and disease-free months, of OXT and OXTR genetic alterations in PC and HCC cases by analyzing information regarding these alterations from The Cancer Genome Atlas (TCGA). Overall, we found that PC and HCC patients with genetic alterations in OXT and OXTR have poorer outcomes. The findings from this study indicate that miR-198 targets c-MET in PC and suggests that miR-198 plays a role in PC chemoresistance. Further, OXT and OXTR are important in PC and HCC progression and survival in a subset of patients. OXT and OXTR, therefore, could potentially have prognostic and therapeutic implications in a subset of PC and HCC patients.

This work is embargoed and will be available for download on Thursday, June 02, 2022

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