Graduation Date

Fall 12-14-2018

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Programs

Biochemistry & Molecular Biology

First Advisor

Dr. Surinder Kumar Batra

Abstract

Pancreatic Cancer (PC) is one of the vicious cancers as it ranks third in the race of leading cause of cancer-related death. Lack of early diagnostic marker, poor understanding of molecular mechanism of the disease and failure to conventional chemotherapy makes this disease dreadful.

Mucin 4 (MUC4), a high molecular weight glycoprotein is one of the top differentially expressed molecules in PC while not expressed in normal pancreas. Accumulating evidence from our lab suggested its tumorigenic role in PC by increasing cell proliferation, invasion, chemotherapy resistance, tumor growth, and metastasis. Previously, our lab and other has identified 24 different splice variant of MUC4 among them MUC4/X is devoid of exon 2 and 3 and MUC4/Y is devoid of exon 2. Exon 2 encodes for the largest domain of MUC4 suggesting that MUC4/X is devoid of the largest domain of MUC4 which variable tandem repeat. Though lots of effort has been made to identify its role in PC, there is still a gap on understanding its splice variant in PC as splice variant has an invaluable role in tumor pathogenesis. Recently splice variant has emerged as one of the key players for tumorigenesis and MUC4 is one of the key players for PC pathogenesis, we aim to identify the functional and mechanical role of MUC4/X, a splice variant which is devoid of the largest domain of MUC4 yet contains all other functional domain, in PC pathogenesis.

Thus, in this part of dissertation, we sought to identify the role of splice variant MUC4/X, a unique splice variant of wild-type MUC4 which contain all functional domain except largest tandem repeat. First, we identified that, MUC4/X in aberrantly expressed in poorly differentiated PC clinical sample. Then our invitro experimental evidence suggested overexpression of MUC4/X in PC cells is involved in increased cell proliferation, invasion and metastasis. Moreover, our orthotopic transplantation system also corroborated our in-vitro findings which showed increased volume of tumor and metastasis to distant organ. Using inducible tet-on system to overexpress MUC4/X in the presence of WT-MUC4 in CAPAN-1 cells, we identified that MUC4/X has increased cell proliferation and invasion suggesting their role as tumorigenic alone as well as in the presence of WT-MUC4. Our mechanical investigation indicate that overexpression of MUC4/X led to upregulation of integrin β1-FAK-ERK pathway which might be potential mechanism for MUC4/X mediated PC tumorigenesis.

Lack of early effective diagnostic marker and resistance to chemotherapy are the major reasons for poor PC patient outcome. There is a pressing need to identify highly specific and sensitive biomarker as well as precise understanding of chemoresistance of PC. Trefoil factors (TFFs) are small secretory molecules mostly associated with mucin. Their primary role is to protect gastrointestinal tract partnering with mucin. Report on aberrant expression, potential as biomarker and role in tumorigenicity has conveyed for many cancers, however, their role in PC is still elusive. Recently they have emerged as a part of gene signature of classical subtype of PC, a subtype which showed gemcitabine resistance towards PC. As it is high time to identify effective biomarker and understanding the role of chemoresistance in PC, in this part of my thesis, we focused to evaluate TFFs diagnostic potential using a training and validation cohort of PC clinical sample. Here, we comprehensively investigated the diagnostic potential of all the member of trefoil family, i.e., TFF1, TFF2, and TFF3 (TFFs) in combination with CA19.9 for detection of PC. In silico analysis of publicly available datasets and expression analysis from human and spontaneous PC mouse model revealed a significantly increased expression of TFFs in precursor lesions and PC cases. Additionally, we performed a comprehensive analysis in the sample set (n= 377) comprising of independent training and validation set using ELISA consisted of benign controls (BC), chronic pancreatitis (CP), and various stages of PC. Our analysis revealed that TFF1 and TFF2 were significantly elevated in early stages of PC in comparison to BC (P

Additionally, we also aim to identify the molecular landscape of TFFs role in gemcitabine resistance of PC which integrates analyzing publicly available cancer genome dataset, dissecting transcriptomic and signaling pathways and identification of biochemical interaction. From TCGA database analysis revealed a significant positive correlation between TFF1 and GR predictor of PC (P=0.0001). Our in vitro studies showed that SW1990-TFF1-KD cells induced apoptosis, reduced colony formation capacity and modulated many apoptotic regulators such increase of cleaved caspases and decrease of CIAP in the presence of gemcitabine. Furthermore, TFF1 was observed to be colocalized with MUC5AC, in human and mouse PC tissues suggesting their partnering are critical for PC pathogenesis. Interestingly, our chromatin immunoprecipitation indicates that 16 fold enrichment of GATA-6, an overexpressed transcription factor in classical subtype of PC, was observed on two distinct TFF1 promoter sites and GATA-6-siRNA repressed expression of TFF1. Moreover, protein-protein docking studies revealed the interaction of TFF1 with CXCR4 at Phe-172, Ser-122 and Glu-1 and TFF1 recombinant protein treatment in SW1990 cells increased CXCR4 mediated downstream signaling critical for GR. In this part, our overall data demonstrate that TFF1 may play a crucial role in gemcitabine resistance which is regulated by GATA6 and by interacting with MUC5AC.

Comments

N/A

Available for download on Saturday, December 05, 2020

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