Interactions between the IGF system and cholesterol metabolism in breast cancer

Abstract

Dyslipidemia and obesity are associated with an increased risk of breast cancer. Several obesity-related host factors involved in systemic metabolism can influence tumor initiation, progression, and/or response to therapy.
Insulin like growth factor (IGF) signalling and levels of cholesterol, particularly low-density lipoprotein cholesterol (LDL-C) and its oxysterol metabolite 27-hydroxycholesterol (27OHC) are frequently up-regulated in obese women. Although high expression of LDL and 27OHC have been reported in breast cancer, their role remains to be elucidated. Triple negative breast cancer (TNBC) accounts for 50% of all deaths as they have a high affinity to metastasize to other organs. TNBC are associated with a poorer outcome because there is no specific target for therapy, such as progesterone receptor (PR), the estrogen receptor (ER)-α, or human epidermal growth factor receptor 2 (HER-2) receptor, that are expressed by other sub-types of breast cancer. The major problem for the failure of breast cancer treatment in TNBCs is the development of resistance to chemotherapy.
In this study, we examined the effect of cholesterol and its metabolite on breast cancer cell proliferation, migration and invasion and the association of the IGF axis and cholesterol metabolism. Human epithelial like estrogen receptor-α (ERα)-positive MCF-7 and T47D and ERα-negative MDA-MB-231 and Hs758T, breast cancer cells were used in this study. Crystal Violet (CV) proliferation assays were employed to detect cell growth and the changes in cell migration were determined using a trans-well migration assay followed by crystal violet staining. Western immunoblotting was used to determine changes in protein abundance. Secreted levels of IGF-I were measured using a radioimmunoassay.
We found that LDL promotes cell growth and migration, and this action was mediated through CYP27A1 in both ERα-positive and ERα-negative breast cancer cells. Treatment with 27OHC also increased cell growth in ERα-positive breast cancer cells and this effect was mediated through ERα. 27OHC was able to promote breast cancer cell migration and invasion in all cell lines, and in the ERα-positive cells, silencing the ERα did not affect this and we found that in ERα-negative cells this action was mediated through estrogen receptor β (ERβ). The addition of LDL increased the production of IGF-I and the abundance of the IGF-IR in MCF-7 and MDA-MB-231 cells. Inhibition of the insulin-like growth factor receptor using a tyrosine kinase inhibitor, AG1024, blocked the effects of cholesterol on cell growth and migration of MCF-7 and MDA-MB-231 cells. The inhibition of insulin-like growth factor-1 receptor attenuated cholesterol-induced AKT and MAPK activation. We also found that chemotherapy treatment such as doxorubicin was less effective in inducing cell death in the presence of 27OHC or LDL in, MDA-MB-231, TNBC cells.
In conclusion, 27OHC functions as a biochemical mediator of the effects of LDL on breast cancer cell growth and migration. 27OHC promotes cell proliferation through ERα, but increased cell migration and invasion through ERβ, and this resulted in intrinsic activation of oncogenes such as IGF-1, which can bind to the IGF-1R and activate MAPK/ PI3K/AKT signalling pathways. Our data also suggest that 27OHC or LDL can act as survival factors in TNBC. The results suggest that using cholesterol lowering drugs such as, statins, may sensitize cells to existing targeted therapies and improve the effectiveness of chemotherapy.

Date of Award	11 May 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Claire M Perks (Supervisor), Jeffrey Holly (Supervisor) & Hanna Zielinska (Supervisor)