|Author||: Arokia Priyanka Vaz|
|Release Date||: 28 September 2021|
|Pages||: 486 pages|
|Rating||: /5 ( users)|
Cancer is a devastating disease that claims the lives of countless people due to its uncontrolled growth pattern. Among various cancers, pancreatic cancer is one of the most lethal cancers due to its aggressive nature, lack of early symptoms and resistance to chemotherapy. The molecular profile of this deadly malignancy is not completely understood. Malignancy arises due to loss or gain of function in genes involved in cell cycle progression leading to disruption of tightly regulated transitions. In addition the evolving concept of cancer throws light on a small population of cells within the tumor known as the cancer stem cells (CSCs) or tumor-initiating cells that are resistant to all drugs treatment and contributes towards tumor initiation and recurrence. Several studies have been carried out to identify specific markers for the cancer stem cell population including that of pancreatic cancer. Pancreatic Differentiation 2 (PD2) or human Polymerase Associated Factor 1 (hPaf1) is an important component of the multifunctional PAF1 complex initially identified to play a crucial role in transcriptional elongation of genes. During the last decade, several papers on PD2 showed that it is a multifaceted molecule playing roles in cell cycle regulation, stem cell maintenance, histone methylation, chromatin remodeling and acinar-to-ductal metaplasia. In this dissertation, the first goal was to investigate the role of PD2 in pancreatic cancer stem cells. Initially, we analyzed the expression and function of PD2 in pancreatic cancer stem cells isolated from pancreatic cancer cell lines, Kras (G12D); Pdx1 (Cre)(KC), Kras (G12D); Trp53 (R172H/+.); Pdx1(Cre) (KPC) mouse models and human pancreatic tumors. Furthermore, the expression of PD2 was significantly higher in CSCs isolated from pancreatic cancer cells along with CSC markers. These cells were shown to exhibit a cobblestone appearance, increased tumorsphere formation and significant tumor growth, characteristic of the CSC phenotype. interestingly, PD2 was found to be specifically overexpressed in a subpopulation of cells within mouse KC, KPC and human pancreatic tumors, which co-express CSC markers. The drug resistance property was impaired upon knockdown of PD2 with simultaneous alteration in the CSC phenotype and reduction in CD133 and MDR2 gene expression. Overall, my study identified that PD2 has a role in self-renewal and drug resistance of pancreatic CSCs. The second part of my dissertation was primarily focused at exploring the functional role of PD2 in pancreatic cancer cells. The ectopic overexpression of PD2 resulted in increased growth rate of tumor cells both in vitro and in vivo. Overexpression of PD2 led to increased growth, colony formation and migration. Interestingly, elevated expression of PD2 also increased the percentage of CSCs. Furthermore, in vivo studies revealed that PD2 overexpression leads to increased tumor volume and metastasis to distant secondary sites. These results were corroborated at the protein level where elevated expression of PD2 led to the up-regulation of c-Myc which is an important player in tumorigenesis and metastasis. In addition, the expression of PD2 in pancreatic cancer tissues and in vitro pancreatic progression model was elucidated. We demonstrated that the expression of PD2 was increased in the ducts present in the pancreatic cancer tissues when compared to the normal tissues. Likewise, the expression of PD2 was elevated in the transformed Human Pancreatic Nestin expressing (HPNE) cells when compared to the untransformed HPNE cells. Understanding the role of PD2 through cell lines led to my next aim to generate PD2 conditional knockout mice in order to substantiate our earlier work in cancer stem cells and acinar to ductal metaplasia during PC initiation. The animal model would be an important resource for understanding the role of PD2 in detail. Taken together, our findings demonstrate that PD2 is an essential member of the oncogene family that plays a significant role in facilitating drug resistance and cancer stem cell maintenance thereby acting as a positive regulator of cancer.