Novel molecular targets in biological processes associated with ovarian cancer metastasis
High grade serous ovarian carcinoma (HGSC) is characterized by an early dissemination of tumor cells and the accumulation of ascites, which provides a unique tumor-supportive microenvironment. Despite decades of research, the mortality rate has not improved, underscoring the need to identify novel t...
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|High grade serous ovarian carcinoma (HGSC) is characterized by an early dissemination of tumor cells and the accumulation of ascites, which provides a unique tumor-supportive microenvironment. Despite decades of research, the mortality rate has not improved, underscoring the need to identify novel targets to improve current therapy.
The present thesis focused on the early metastatic dissemination of HGSC cells and the underlying molecular mechanisms. Genetic analysis of tumor cell spheroids and corresponding solid tumor masses (primary lesions and metastases) showed that HGSC cells acquire few new mutations during progression, except for mutated FAT3 and RAD51A/C, which were enriched in metastases. RNA sequencing revealed increased mesenchymal gene expression in attached HGSC cells both in vivo and in vitro, hinting to an epithelial-mesenchymal-transition. Intriguingly, this switch included upregulation of a specific subset of mesothelial genes, such as podoplanin (PDPN) and calretinin (CALB2), which was associated with a poor clinical outcome. Calretinin-positive cells were seen in spheroids as well as in metastases, with frequent accumulation at the invasive front. Decreased calretinin expression resulted in loss of adherence in all tested primary as well as established HGSC cell lines, revealing calretinin as a potential therapeutic target for interfering with the early adhesion and invasion process.
In the second part of this work, the role of lysophosphatidic acid (LPA), which accumulates in ascites and correlates with poor relapse-free survival, was investigated in detail. Our data show that LPA regulates the transcriptome via ROCK, ERK and PKC to promote cell motility and migration of patient-derived HGSC cells. Mass-spectrometry-based analysis of LPA-induced changes in the phosphoproteome revealed a complex signaling network, where a majority of pathways lead to changes in actomyosin dynamics, with a central role for LPAR1, the trio – ROCK, ERK and PKCδ and their downstream target MYPT1. MYPT1 negatively regulates the phosphorylation of myosin light chain (MLC2) and correlates with poor survival of HSGC patients. LPA induced a contractile phenotype in HGSC cells, concomitant with p-MLC and p-MYPT1 colocalizing with F-actin and p-PKCδ relocating to the cell edges. LPA-induced cell motility and cell-in-cell invasion (entosis) were sensitive to pharmacological inhibition of ROCK, ERK or PKC. In coherence with these findings, downregulation of MYPT1 via siRNA interference hampered cell migration and entosis. These findings suggest that MYPT1 may represent a new promising candidate for therapeutic intervention with HGSC cell migration and invasion. Finally, we identified a novel LPAR2-DOCK7 axis, which is essential for the entotic process and thus may also have translational significance.