Understanding STAT3 in cystic fibrosis better – Interview with PD Dr. Frauke Stanke

BREATH scientist PD Dr. Frauke Stanke and her working group at Hannover Medical School, in a project started in 2016, investigated what role the protein STAT3 plays in the formation of cystic fibrosis transmembrane conductance regulator (CFTR) channels in the cell. The STAT3 gene has been described in previous work as the modifying gene for cystic fibrosis. The coded protein from the gene, STAT3, acts as a transcription factor, which controls in the cell the extent to which the approx. 20,000 human genes are expressed. In the meantime, however, it is known that STAT3 is at the same time also involved in signal cascades, which influence the immune response.

Preliminary work in the project had shown that STAT3 is a modified cystic fibrosis gene and influences the CFTR residual activity gene in F508del-CFTR homozygous patients. The aim of the project started in 2016 was therefore initially the role of STAT3 as a transcription factor and  the effect of STAT3 on the expression of mature, completely glycosylated CFTR protein. We have spoken with Frauke Stanke about the results of the project.
Frauke Stanke’s team published the results of the project in the specialist journal „Human Molecular Genetics“ and gave an interview to the Mukoviszidose e.V. about the ongoing research. 

Which question(s) should your project answer?

Transcription factors tell the cell which genes can be transcribed and translated into proteins and which genes, or their proteins, are not currently required. When researchers talk about gene expression, they mean the transcription and production of the coded protein in the gene. There are many different transcription factors. Even the expression of the cystic fibrosis gene CFTR is regulated  via transcription factors.  So far, so good – but at the start of the project it was not known whether the transcription factor STAT3 is able to directly influence the expression of the gene’s CFTR and thus the production of the CFTR channel. The CFTR protein acts as a chloride and bicarbonate channel on the outward-facing cell surface of airway cells and other surface cells and regulates the liquid film in the airways. The project aims to show whether a procedure in the cell to reduce the effect of STAT3, also leads to a reduction of CFTR protein.

Could all experiments be carried out as planned?

Yes, they could – but unfortunately the planned cell culture experiments which we carried out then prompted further questions. We were only able to show the predicted effect „less STAT3 function leads to less CFTR protein“  for one of the two cell lines examined, which we were unable to explain. In order to find an answer, we have added a retrospective clinical observation study to establish whether more or less STAT3 is good for cystic fibrosis patients. For this observational study we have retrospectively looked at the clinical course of approximately 140 cystic fibrosis patients (all F508del homozygous), who were treated at the Cystic Fibrosis Center in Hannover. In addition, information on the STAT3 genes from earlier studies was also available for these patients. We were thus able to connect the documented clinical data with the genetic information in STAT3. The amount of STAT3 formed in the cells can be derived in all people with the help of this genetic marker.
What answers does the project provide?

With the cell culture experiments and the clinical data we have been able to show that, in the pulmonary epithelial cells less STAT3 leads to more CFTR protein. However: the observation of cystic fibrosis patients, born between 1959 and 1994 and treated at the Cystic Fibrosis Center in Hannover, showed that this is not a disadvantage. On the contrary: in patients born before 1970, those who could produce a large amount of STAT3 had an advantage.

What do your results mean for CF patients?

We interpret our data as follows: the role of STAT3 in the respiratory tract surface cell is important for the amount of CFTR protein, where it applies that less STAT3 is good for more CFTR protein. In other somatic cells – e.g. in immunologically relevant cells – less STAT3 is not particularly helpful, since less STAT3 may perhaps weaken the immune response and possibly ease infections. Thus, less STAT3 for patients born before 1970 could even be harmful. In patients who were born later than 1970 – that is at a time when good therapeutic countermeasures against infections were possible – the genetic predisposition of STAT3 is not crucial for the clinical outcome. The influence of STAT3 on the disease process in cystic fibrosis is now better understood – even if the results now call rather for restraint, whereas at the start of the project STAT3 was perhaps still considered to be the therapeutic objective to improve the CFTR production. This is still the case for CFTR-expressing epithelial cells, but a systemic therapeutic approach – which would also affect immune cells – is not the main target.
From our investigations, however, we also learn that studies in which the clinical course spans a very long period of time, must also always include the changes in CF therapy.

Are there restrictions in the interpretation of your results?

It is possible that the therapy has an influence on whether the transcription factor STAT3 has a clinically relevant effect on CFTR – at least in the patient cohort in Hannover, which we have examined in the observational study, everything pointed to this. The results cannot, however, be generalized for all cystic fibrosis patients.

What are your further research plans on this issue?

We are currently evaluating the data on patient pairs from Europe in order to ascertain whether the observed effect can also be seen in other patient collectives. In addition, we would like to name which immune cells are responsible for a high STAT3 expression being advantageous for patients born before 1970. The genetic marker in STAT3 records the predisposition very reliably and is also particularly suited to look into this question. These results could help to better understand the role of STAT3 in cystic fibrosis for CFTR-expressing epithelial cells and immune cells and be able to provide more targeted therapy.

For this project, Mukoviszidose e.V. has provided a grant and research material for an experimental doctoral thesis. For further questions, the German Center for Lung Research (DZL) will provide finance so that PD Dr. Stanke and her team can continue their cystic fibrosis research in the long term at the Hannover site.

Text: Mukoviszidose e.V.

Photo: privat

PD Dr. Frauke Stanke

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PD Dr. Frauke Stanke