Transkriptionsregulation der Pyruvatdehydrogenase-Kinase 4 (PDK4), einem zentralen Schalter des Glukosestoffwechsels, durch Zelladhäsion und onkogene Signalwege beim humanen Ovarialkarzinom

Ovarian cancer is the most lethal of all gynecologic malignancies mainly due to the passive dissemination of cancer cells within the peritoneal cavity. Thereby tumor cells detach as single cells or multicellular spheroids from the solid tumor nodules and spread via the peritoneal fluid to form metastases. Matrix detachment is therefore of high clinical relevance and thus warrants further investigations of the molecular mechanisms. The present work identified PDK4 as a gene that is strongly upregulated in primary human ovarian cancer cells and the ovarian carcinoma cell line SKOV-3 upon detachment. Moreover, the induction of PDK4 could be linked to the glycolytic metabolism in these cells consistent with the known function PDKs to inactivate pyruvate dehydrogenase and thereby suppress oxidative phosphorylation. It is also shown that interactions between components of the extracellular matrix and integrins regulate adhesion-dependent PDK4 expression. Therefore, a main part of this work focuses on a detailed interrogation of transcriptional control mechanisms acting on the PDK4 gene and the identification of signaling pathways controlled by adherent or non-adherent conditions in SKOV-3 cells. Following pharmacological modulation of different signaling pathways or siRNA-mediated silencing of specific signaling proteins, the phosphorylation of critical signaling components, chromatin binding and transcriptional PDK4 activity were determined. These studies showed that multiple pathways might cooperate in PDK4 induction upon detachment, including the SRC-PI3K-AKT-pathway, the GSK3-β-Catenin pathway, the estrogen receptor, the transcription factor C/EBPβ and cytoskeletal rearrangements. Beyond PDK4 regulation under different adhesion conditions this work revealed a complex transcriptional control of PDK4 expression by oncogenic signaling in ovarian cancer cells. Thus, activation of the adenylyl cyclase-PKA-cAMP pathway, inhibition of the SRC-PI3K-AKT pathway as well as estrogen, glucocorticoids and cell-cell contacts were found to induce PDK4 expression. Taken together, the complex regulation of PDK4, including its induction by oncogenic pathways, and its central position in glucose metabolism point to a pivotal role of PDK4 in tumor metabolism and its potential as a therapeutic target for ovarian carcinoma.