A crosstalk between NF-κB and STAT1 signal transduction pathways in ischemic and proliferative diseases

by Sana Mumtaz Sheikh
Doctoral thesis
Date of Examination:2023-08-16
Date of issue:2024-07-08
Advisor:Prof. Dr. Thomas Meyer
Referee:Prof. Dr. Dieter Kube
Referee:Prof. Dr. Niels Voigt
Referee:Prof. Dr. Frauke Alves
Referee:Prof. Dr. Oliver Wirths
Referee:PD Dr. Antje Ebert
Persistent Address: http://dx.doi.org/10.53846/goediss-10601

 

 

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Abstract

English

The cytokine-driven transcription factor STAT1 (signal transducer and activator of transcription 1) executes anti-microbial and pro-apoptotic functions, while loss-offunction mutations in the STAT1 gene are associated with an increased susceptibility to microbial infections. Transgenic mice expressing a truncated STAT1 protein lacking its amino-terminal domain frequently develop splenomegaly due to the formation of a non-Hodgkin lymphoma. Histopathological examination revealed that the expression of the recombinant STAT1-N variant frequently resulted in the disruption of the normal splenic architecture by malignant tumor cells with a positive immunostaining for both tyrosine-phosphorylated STAT1 and STAT3. Immunoblotting of lysates from isolated tumor cells confirmed the cytokine-independent hyperphosphorylation of the two STAT proteins, whereas the expression level of NF-κB was significantly reduced. Gel-shift assays demonstrated an elevated DNA-binding activity of STAT1-N as compared to the wild-type protein. The elevated level of tyrosine-phosphorylated STAT1 did not increase further upon stimulation of the isolated tumor cells with either interferon-γ (IFNγ), lipopolysaccharide (LPS), or a combination of both. Since the mutant STAT1 was unable to accumulate in the nucleus upon cytokine stimulation, real-time PCR data from tumor tissue as well as from IFNγ/LPS-treated lymphoma cells demonstrated significantly reduced STAT1-regulated target gene expression despite its observed hyperactivation. The nuclear import defect of tyrosine-phosphorylated STAT1-N was associated with an elevated tyrosine-phosphorylation level of its antagonistic homolog STAT3, which is a known oncogene. To further address the putative beneficial effect of early immune inflammation, the effects of LPS pretreatment by peritoneal administration was tested in the transgenic STAT1 mice model with a loss-of-function mutant resulting from the deletion of its amino terminus. Results showed a significant decrease in tyrosine phosphorylation of STAT1 in isolated splenocytes from LPSpretreated mice stimulated ex vivo with interferon-γ (IFNγ) as compared to the untreated mice. In contrast, tyrosine phosphorylation of STAT3 remained unaltered. Furthermore, a significant decrease in the expression of STAT1-regulated target genes in LPS-pretreated mice was observed. Thus, the data reveal that the lack of STAT1 nuclear accumulation interferes with the functional balance between STAT1 and STAT3, thereby promoting tumorigenesis. Since repeated fecal microbiota transplantation (FMT) had adverse hemodynamic effects in wild-type mice as 11 compared to saline-treated mice with myocardial infarction, it will be interesting to characterize this mutant in the setting of a comorbid ischemic and infectious disease.
Keywords: tyrosine-phosphorylated; hyperactivation; expression