Studies on Proteins Influencing Cancer Progression and Regulating Endocytic Lipid Trafficking
Year: 2017
Type: dissertation
Abstract: Endocytosis is a form of active cellular transport by which cells internalize molecules from the extracellular environment. This thesis studies proteins involved in endocytosis that influence the progression of cancers in humans. Two of the three articles summarized here employ cell biological experiments to elucidate the role of the proteins N-muc downstream-regulated gene 1 (NDRG1) and StAR-related lipid transfer protein 3 (StARD3) in the regulation of endocytic trafficking. The third article describes a novel data analysis method and its application to a large data set of breast cancer patients. We studied the effects of NDRG1 protein depletion on cellular cholesterol content and distribution, low-density lipoprotein receptor (LDLR) localization and turn-over, and the morphology of endosomal organelles. We found that depletion of the NDRG1 protein leads to reduced abundance of LDLR on the plasma membrane (PM) and as a result, reduced LDL uptake. When NDRG1 is depleted, LDLR accumulates in multi-vesicular bodies (MVBs), and while LDLR ubiquitination is increased, its degradation is decreased. The PM levels of LDLR and LDL uptake are rescued upon co-depletion of the inducible degrader of the LDL-receptor (IDOL). Our findings identify NDRG1 as regulator of MVB formation and trafficking. We also found that elevated levels of StARD3 protein alter the cholesterol balance and adhesiveness of breast cancer cells. We studied the effects of StARD3 overexpression in cells, as well as the association of StARD3 protein levels with cancer progression markers in Finnish breast cancer patients. We found that in MCF-7 cells, stable StARD3 overexpression altered the morphological features and the cholesterol balance of the cells. In the breast cancer tumor samples from patients, high StARD3 protein levels associated with ERBB2 (receptor tyrosine-protein kinase erbB-2) amplification. High protein levels also associated with proto-oncogene tyrosine-protein kinase Src (Src) activation and increased 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) transcript levels. Our findings suggest that elevated StARD3 levels contribute to breast cancer aggressiveness. Finally, a systematic approach to data analysis was developed and demonstrated by applying it to an existing data set of breast cancer patients. High-throughput molecular level data and clinical data were integrated in the study. This revealed a coamplification of NDRG1 and the gene lysosomal-associated transmembrane protein 4B (LAPTM4B), encoding an endosomal protein that regulates ceramide trafficking, and discovered new genes potentially coregulated with LAPTM4B.
Source: Työväentutkimus Vuosikirja
Author: Boris Vassilev
Language: English
Subfield: Cancer Research
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2615054372