Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Arzt, L.
The role of the STAT signaling pathway in the regulation of growth and apoptosis in malignant pleural mesothelioma
Doktoratsstudium der Medizinischen Wissenschaft; Humanmedizin; [ Dissertation ] Medical University of Graz; 2014. pp. 103
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Höfler Gerald
- Popper Helmuth
- Samonigg Hellmut
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- Abstract:
- Malignant pleural mesothelioma (MPM) is an aggressive tumor caused by former asbestos exposure with a mean overall survival of 12 months from diagnosis. The knowledge about prognostic factors of outcome is poor and MPM is resistant to conventional therapy. Genetic predisposition even contributes to the development of MPM: BRCA1-associated protein 1 (BAP1) is a tumor suppressor gene that is frequently lost in MPM and germline mutations predispose to several different tumors including MPM. We wanted to know if BAP1 expression could be used as prognostic factor of outcome and we detected a significant effect of BAP1 expression on overall survival time: the higher the BAP1 expression (non-mutated BAP1), the shorter the overall survival. From our recent study and published data we know that the regular rapid progressive type of MPM uses several signaling pathways regulating cell growth and survival. The JAK/STAT signaling pathway is the principal signaling mechanism for lots of cytokines or growth factors in mammalians. Our investigations demonstrate that the STAT (signal transducer and activator of transcription) signaling pathway is totally deregulated. STAT1 is upregulated, phosphorylation of STAT1 on tyrosine 701 is induced by Interferon-gamma treatment and it is very likely that STAT1 functions as an oncogene through the STAT1/survivin pathway. Survivin is highly expressed in MPM and is associated with resistance to chemotherapy. STAT3 is downregulated in MPM and only a very small part is activated by phosphorylation, which indicates that it has no oncogenic function in MPM. The negative regulators SOCS1 (suppressor of cytokine signaling) and SOCS3 were not detected on protein level and therefore STAT1 activation is not terminated. However, it was possible to detect SOCS messengerRNA (mRNA) in MPM cell lines. This means that the translation process is inhibited or affected by something. It is known that protein expression is controlled by non-coding RNAs and microRNAs (miRNA) are one class. They regulate the expression of target mRNAs and are expected to act as oncogenes or tumor suppressors. Therefore we aimed to quantify selected miRNAs in MPM which are thought to be involved in the regulation of the STAT signaling pathway. Four upregulated miRNAs (miR-19b, miR-30b, miR-30c and miR-222) have been identified, possibly targeting SOCS1/3 and we tried to re-express SOCS1/3 in MPM cell lines by knocking down the identified miRNAs using single inhibitors or combinations of inhibitors. With these experiments we aimed to answer if the STAT1/3 signaling cascade can be restored to a physiological level when SOCS proteins are expressed again. Since the knock-down had no effect on SOCS protein expression, it seems that the miRNAs identified by now, are not the (only) reason for the missing expression of SOCS1/3. To clarify if components of the deregulated STAT signaling pathway have potential as therapeutic targets, it was investigated if the knock-down of STAT1 in MPM cell lines leads to an increased expression of apoptosis or cell-cycle related genes. The effect of STAT1 knock-down on the expression of STAT proteins was different in MPM cell lines: while CRL-5915 seems to compensate STAT1 knock-down by an upregulation of STAT5a, MSTO-211H and Hmeso show slightly upregulated expression levels of STAT3. Most of the genes investigated were found to be differentially expressed in all cell lines, but STAT1 knock-down seems to have an effect on cell cycle progression and apoptosis by the upregulation of CDKN1A in all MPM cell lines. However, it is very unlikely that cell cycle and apoptosis are regulated by only one gene especially because no cell growth inhibition was detected microscopically after STAT1 knock-down. Understanding the role of STATs in MPM could be the first step into the development of a targeted therapy for these tumors.