The role of lipid signaling components in breast cancer: From early events of epithelial apical polarity loss to estrogen negative invasive carcinoma
Abstract
As of now, there is very little understanding of the mechanisms that initiate breast cancer and permit the design of cancer prevention strategies. Using a cell system that recreates phenotypically normal, basoapically polarized, mammary epithelium we demonstrated that loss of apical polarity is an early change that is necessary for tumor development. With this model we determined that factors involved in modulating breast cancer risk, dietary lipids (ω-6 fatty acids) and the lipid metabolic inflammatory pathway, induced loss of apical polarity. Alterations in apical polarity also involved changes in gene expression of CDS1, the gene that codes for a lipid enzyme, upstream of the oncogenic lipid-dependent PI3K signaling pathway. Therefore, my research hypothesis is that lipid-dependent signaling is linked to apical polarity stability, and such a relationship plays a role in the maintenance of breast epithelial homeostasis. In the first part of my work, I demonstrate that ω-6 arachidonic acid (AA)-induced disruption of apical polarity encompasses the redistribution of the core tight junction proteins, ZO-1, and ZO-2, and of the polarity regulatory proteins, Cx43 and Scrib. Loss of apical polarity is accompanied by changes in cell membrane lipid organization without an accumulation of AA at the cell membranes. Previous observations suggest that PI3K mediates AA disruption of apical polarity. However, the activity of PI3K downstream effector AKT appears necessary for apical polarity maintenance. Finally, breast acini that loose apical polarity after AA treatment enter the cell cycle upon growth factor stimulation, whereas cells that retain apical polarity do not. Overall, AA is able to alter breast epithelial organization, weakening proliferation-arrest and increasing the risk for breast cancer development. In the second part of my work, I investigated the role of the CDS1 gene in breast cancer. CDS1 influences the synthesis of phosphatidylinositols involved in several key cell-signaling processes for breast homeostasis. I have confirmed that CDS1 expression is linked to apical polarity status in cell culture and in breast tissue. Interestingly, CDS1 protein levels are greatly decreased in estrogen negative invasive cancers with adverse prognosis. Yet, de novo expression of CDS1 is not sufficient to revert the cancerous phenotype of aggressive MDA-MB-231 breast cancer cells. A potentially modified form of the CDS1 protein, as shown by a higher molecular weight on western blot obtained from cancer cells, is present in MDA-MB-231 cells transfected with the CDS1 construct. Further analysis of CDS1 expression reveals the possibility of gene silencing through promoter methylation, and a potentially modified form of the protein in cancer cells that remains upon CDS1 transfection. CDS1 is an interesting novel target to pursue for breast cancer research as it could influence early events in breast cancer onset as well as the progression of aggressive forms of cancer.
Degree
Ph.D.
Advisors
Lelievre, Purdue University.
Subject Area
Molecular biology|Cellular biology|Oncology
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.