From cell surface to nucleus:Unraveling cancer metastasis and the role of nucleophosmin in breast cancer
Year: 2013
Type: dissertation
Abstract: The most deadly aspect of cancer is its ability to spread from its original location to other sites in the body and grow as distant metastases. Formation of metastases is a multistep process and metastases can form even decades after the removal of the primary tumor. Cell surface proteins are known to play central roles in the adhesive contacts and molecular interactions between the tumor cell and the stroma during various stages of metastasis. In addition, they mediate important signals to intracellular proteins. As the detailed mechanisms of metastasis are still unclear, the aim of this thesis was to discover novel metastasis-associated cell surface proteins for further investigation. This thesis established an optimized method for the isolation of biotinylated cell surface proteins for proteomic identification. This method was applied to compare the cell surface proteins isolated from an isogenic pair of human MDA-MB-435 cancer cell line with opposite metastatic phenotypes. We found 29 differentially expressed proteins and analyzed the molecular pathways they were involved in. Of these proteins expression of CD109 was shown to mark metastatic melanoma cells and invasive breast cancer cells. Nucleophosmin (NPM) is a multitasking protein with both oncogenic and tumor suppressive functions. In our comparative proteomics analysis we discovered NPM to be expressed on the surface of the non-metastatic subclone of the MDA-MB-435 cells. We showed that NPM was detected at different localizations in the non-metastatic and metastatic cells most likely due to the expression of novel NPM splice variants discovered in this thesis work. In addition, we showed that expression level of NPM is one mechanism affecting its localization. In regards to patient prognosis, we revealed that high levels of NPM were expressed in the luminal epithelial cells of histologically normal breast tissue and that high levels independently associated with good prognosis in the luminal A breast cancer subtype. On the contrary, novel granular staining pattern and Threonine199 phosphorylation of NPM (NPMpThr199) correlated with aggressive characteristics, basal subtype and poor prognosis of human breast cancer. In brief, this study provides several novel metastasis associated cell surface proteins for future investigation. By using breast cancer tumor microarrays from two large breast cancer patient cohorts and cellular models this thesis demonstrates for the first time, that different NPM forms play divergent and opposite roles in breast cancer.
Source: Työväentutkimus Vuosikirja
Author: Piia‐Riitta Karhemo
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1527100301