The capability for expansive tumor growth is described as a key hallmark of cancer. Discovering the mechanisms driving this proliferative capacity could advance new targeted therapies to inhibit tumor growth, recurrence, and metastasis. With the aim of identifying new components of the regulatory circuit driving tumor growth, we studied the role of Chaperonin-Containing TCP1 (CCT or TRiC) in promoting breast cancer. CCT is a cytosolic protein folding macromolecular complex composed of eight subunits (CCT1-8) that interacts and assists in the folding of a number of substrates including oncoproteins and mutated tumor suppressors. Recent findings from our lab and others revealed that the second subunit, CCT2, is specifically upregulated and causes uncontrolled growth in breast cancer as shown by CCT2 overexpression and depletion studies. In 3D and 2D cultures of luminal A breast cancer cells, T47D and MCF-7, CCT2 overexpression promoted the formation of tumor-like spheroids, increased cell proliferation, and cell cycle progression, and promoted anchorage-independent growth. Importantly, CCT2 gene expression correlated with increased levels of cell cycle promoting genes like MYC, CCND1 (cyclin D1), and CDKN2 (CDK2) and potentially could serve as a hub for converging pro-tumor cell signaling pathways. These findings led to the premise that the upregulation of CCT2 expression in cancer cells could be triggered by stress conditions such as uncontrolled growth in nutrient-poor in vivo conditions. In support, depletion of CCT2 by 40-50% did not affect luminal A breast cancer cells grown in unstressed, nutrient-rich cell culture conditions but did inhibit in vivo tumor growth of metastatic breast cancer cells in mice. Hence, we investigated whether increased CCT2 could be linked to other stress conditions such as those that result in the development of drug resistance to cancer therapies. Inhibitors of the cell cycle mediators, CDK4/6, such as Palbociclib, show significant patient benefit that is offset by the eventual development of resistance. To determine whether CCT2 could have a role in promoting resistance to CDK4/6 inhibition, we treated control and CCT2-overexpressing T47D and MCF-7 cells with Palbociclib. We noted that CCT2-overexpressing cells displayed increased resistance to Palbociclib as compared to control cells and upon long-term culture with Palbociclib recovered faster, with two-four fold increases in cell number after 30 days. These cells retained increased proliferative capacity after treatment cessation, and, in response to Palbociclib treatment, increased CCT2 levels beyond that observed in basal cultures. This increase in CCT2 gene expression correlated with increases in CCND1 and CDKN2, which suggests a possible compensatory mechanism that enables resistance to CDK4/6 inhibition. These findings do not rule other cell cycle independent compensatory pathways such as increased metabolic activity that bears further study. Our findings suggest that CCT2 may be selectively increased in cancer cells in response to stress conditions and, thereby, has an important role in supporting uncontrolled growth in cancer progression and promoting drug resistance. CCT2 could thus serve as a prognostic and therapeutic target for multi- targeted inhibition that would overcome drug resistance and enhance patient treatment outcomes
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:etd2020-2134 |
| Date | 01 January 2021 |
| Creators | Ghozlan, Heba |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Electronic Theses and Dissertations, 2020- |
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