No description available.

Breast cancer (BC) is the second most common malignancy in the world and it accounts for 15% of female deaths due to cancer every year. The development of these tumours is regulated by the activities of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Tamoxifen (TAM) is frequently used to treat patients with ER+ BC; however, a recurring problem is the development of resistance and the mechanisms leading up to this event remain unclear. FAM84B is reported to be associated with the development of various cancers such as esophageal squamous cell carcinoma and prostate cancer. The function of the protein is unknown; however, insight towards its mechanism of action has been made through the discovery of its structural similarities with the H-Ras-like suppressor (HRASLS) subfamily of enzymes. We hypothesize that FAM84B upregulation enhances BC tumorigenesis and facilitates the development of TAM resistance in this disease. We observed that both overexpression and knockdown of FAM84B had little effects on cell proliferation; however, the latter reduced the ability of MCF7 cells to form isolated colonies. We performed similar analyses using a FAM84B mutant with deletion of its HRASLS domain and we observed that MCF7 cells expressing this protein showed higher rates of cell proliferation and increased ability to form isolated colonies compared to cells with baseline expression of wild-type FAM84B. These results suggest that FAM84B regulates BC cell proliferation through a complex manner. An analysis of patient-derived BC tissue revealed that FAM84B expression was associated with BC at early stages than later stages, which suggests a possible role of the protein in directing events associated with the early developmental stages of the disease. Additional analyses demonstrated that overexpression and knockdown of FAM84B had little impact on TAM-derived cytotoxicity of MCF7 cells. We observed higher expression of FAM84B in TAM-resistant MCF7 cells in comparison to TAM-sensitive cells, while TAM-resistant and TAM-sensitive xenograft tumours showed similar levels of FAM84B expression. This suggests that the contributions of FAM84B in BC tumorigenesis and resistance to TAM are complex; alternatively, FAM84B may not play a major role in either events. Future studies will be needed to clarify the effects of FAM84B on BC tumorigenesis and progression. / Dissertation / Master of Science (MSc) / Breast cancer (BC) is the second most common malignancy in the world and it accounts for 15% of female deaths due to cancer every year. Although hormonal therapy with tamoxifen (TAM) is a commonly used treatment for the disease, a recurring problem is that tumours eventually develop resistance to the drug. We are interested in investigating the role of FAM84B in BC tumorigenesis and the development of TAM resistance in these tumours. FAM84B has been shown to have higher expression in esophageal squamous cell carcinoma than in normal tissue and the protein was associated with increased tumour growth. Similar studies in prostate cancer have shown that FAM84B is associated with progression of the disease. The results of our analyses suggest that FAM84B may have a possible role in promoting events associated with enhancing the viability of MCF7 cells, leading to increased rates of growth and division. In addition, FAM84B may also function to direct events associated with the early developmental stages of BC. We did not, however, observe any impact of altered FAM84B expression on the development of TAM resistance in BC. Further research involving improved in vitro and in vivo studies, along with an examination of FAM84B’s impact on various oncogenic molecular signalling pathways, will help improve our understanding of the protein’s role in BC tumorigenesis.

Resistance to antiestrogen therapy remains a significant problem in breast cancer. Low expression of inhibitor of growth 4 (ING4) in primary tumors has been correlated with increased rates of recurrence in estrogen receptor-positive (ER+) breast cancer patients, suggesting a role for ING4 in ER signaling. This study provides evidence that ING4 inhibits ER activity. ING4 overexpression increased the sensitivity of T47D and MCF7 ER+ breast cancer cells to hormone deprivation. ING4 attenuated maximal estrogen-dependent cell growth without affecting the dose-response of estrogen. These results indicated that ING4 functions as a noncompetitive inhibitor of estrogen signaling and may inhibit estrogen-independent ER activity. Supportive of this, treatment with fulvestrant but not tamoxifen rendered T47D cells sensitive to hormone deprivation as did ING4 overexpression. ING4 did not affect nuclear ER alpha protein expression, but repressed selective ER-target gene transcription. Taken together, these results demonstrated that ING4 inhibited estrogen-independent ER activity, suggesting that ING4-low breast tumors recur faster due to estrogen-independent ER activity that renders tamoxifen less effective. This study puts forth fulvestrant as a proposed therapy choice for patients with ING4-low ER+ breast tumors.

A major problem with breast cancer treatment is the prevalence of antiestrogen resistance, be it de novo or acquired after continued use. Many of the underlying mechanisms of antiestrogen resistance are not clear, although estrogen receptor-mediated actions have been identified as a pathway that is blocked by antiestrogens. Selective estrogen receptor modulators (SERMs), such as tamoxifen, are capable of producing reactive oxygen species (ROS) through metabolic activation, and these ROS, at high levels, can induce irreversible growth arrest that is similar to the growth arrest incurred by SERMs. This suggests that SERM-mediated growth arrest may also be through ROS accumulation. Breast cancer receiving long-term antiestrogen treatment appears to adapt to this increased, persistent level of ROS. This, in turn, leads to the disruption of reversible redox signaling that involves redox-sensitive phosphatases and protein kinases and transcription factors. This has downstream consequences for apoptosis, cell cycle progression, and cell metabolism. For this dissertation, we explored if altering the ROS formed by tamoxifen also alters sensitivity of the drug in resistant cells. We explored an association with a thioredoxin/Jab1/p27 pathway, and a possible role of dysregulation of thioredoxin-mediated redox regulation contributing to the development of antiestrogen resistance in breast cancer. We used standard laboratory techniques to perform proteomic assays that showed cell proliferation, protein concentrations, redox states, and protein-protein interactions. We found that increasing thioredoxin reductase levels, and thus increasing the amount of reduced thioredoxin, increased tamoxifen sensitivity in previously resistant cells, as well as altered estrogen and tamoxifen-induced ROS. We also found that decreasing levels of Jab1 protein also increased tamoxifen sensitivity, and that the downstream effects showed a decrease p27 phosphorylation in both cases. We conclude that the chronic use of tamoxifen can lead to an increase in ROS that alters cell signaling and causing cell growth in the presence of tamoxifen, and that this resistant cell growth can be reversed with an alteration to the thioredoxin/Jab1 pathway.

Estrogen signalling pathway plays crucial role in carcinogenesis of breast cancer. Estrogen receptor (ER) is a prototypical hormone receptor that upon binding its ligand, estradiol, translocates into the nucleus and turns on target genes related to cellular proliferation and survival. Although estrogen signalling physiologically supports normal breast tissue development, deregulations of this pathway contribute to development of breast tumours that are estrogen receptor dependent. One of the main obstacles in breast cancer treatment is acquired resistance to common anticancer drugs also known as multidrug resistance (MDR). The switch between chemotherapy responsive to chemotherapy resistant cell phenotype is usually accompanied by increased expression of ABC transporters, special membrane proteins responsible for export of various kinds of commonly used anticancer drugs from the intracellular to extracellular space and is also linked to the existence of cancer stem cells (CSCs). ABC transporters can not only export chemotherapeutic drugs but may modulate tumour microenvironment through the transport of endogenous intracellular substrates such as leukotrienes (LTs), sphingolipids and prostaglandins PGs). This function may also play important role in carcinogenesis. The aim of the thesis was to...

The resistance to tamoxifen, a drug used in the adjuvant therapy for hormone sensitive breast cancer, represents a major clinical obstacle. Although various mechanisms leading to tamoxifen resistance have been described and intensively studied, a significant number of patients still become resistant to the treatment and eventually relapse. Tamoxifen therapy has been shown to enrich tumors with cancer stem cells (CSCs), which are naturally resistant, and have self-renewal ability and the potential to form secondary tumors. Metabolic rewiring, altered iron metabolism and upregulation of ATP-binding cassette (ABC) transporters have been shown to be important in the maintenance of CSC phenotype. Therefore, we investigated these mechanisms as possible contributors to tamoxifen resistance in vitro in two tamoxifen resistant (Tam5R) cell lines that we established. We show that Tam5R cells have dramatically disassembled and less active mitochondrial supercomplexes (SCs) and higher level of mitochondrial superoxide, together with a fragmented mitochondrial network. Such dysfunction of mitochondria results in the AMP-activated protein kinase (AMPK) activation and metabolic rewiring towards glycolysis. Importantly, cells lacking functional mitochondria are significantly more resistant to tamoxifen, supporting...

The resistance to tamoxifen, a drug used in the adjuvant therapy for hormone sensitive breast cancer, represents a major clinical obstacle. Although various mechanisms leading to tamoxifen resistance have been described and intensively studied, a significant number of patients still become resistant to the treatment and eventually relapse. Tamoxifen therapy has been shown to enrich tumors with cancer stem cells (CSCs), which are naturally resistant, and have self-renewal ability and the potential to form secondary tumors. Metabolic rewiring, altered iron metabolism and upregulation of ATP-binding cassette (ABC) transporters have been shown to be important in the maintenance of CSC phenotype. Therefore, we investigated these mechanisms as possible contributors to tamoxifen resistance in vitro in two tamoxifen resistant (Tam5R) cell lines that we established. We show that Tam5R cells have dramatically disassembled and less active mitochondrial supercomplexes (SCs) and higher level of mitochondrial superoxide, together with a fragmented mitochondrial network. Such dysfunction of mitochondria results in the AMP-activated protein kinase (AMPK) activation and metabolic rewiring towards glycolysis. Importantly, cells lacking functional mitochondria are significantly more resistant to tamoxifen, supporting...

The Hsp70 family of molecular chaperones is essential for protein folding, re-folding misfolded client proteins, clearance of aberrant client proteins, and can also inhibit programmed cell death. There are two major cytosolic members of this family: the constitutive Hsc70, and the inducible Hsp72. Under stress conditions the Hsp70 family protects the cell from protein related damage by the induction of Hsp72. Hsc70 and Hsp72 are highly homologous with minor differences in substrate binding. In cancers, Hsp72 is commonly induced and this induction is thought to aid in cancer cell survival. In these studies we demonstrate the differential regulation of the prosurvival kinase Akt by Hsc70 and Hsp72. We demonstrate that of the two cytosolic forms, Hsp72 is the primary Akt regulator. Using a phenothiazine class inhibitor of Hsp70-family activity, methylene blue, we demonstrate dose dependent decreases in the levels of Akt; produced breast cancer specific cell death. This cell death could be rescued by the use of an Hsp70 family ATPase stimulating compound, SW02. We also demonstrate a similar phenotype with a rhodacyanine class Hsp70 family inhibitor, YM-1, also capable of reducing Akt and causing cancer specific cytotoxicity. The resulting Akt decreases were sufficient to block a tamoxifen-resistance pathway, allowing previously resistant cells to regain sensitivity to tamoxifen. These results demonstrate the capabilities of Hsp70 family inhibitors as potent compounds for the treatment of breast cancer.

No description available.