DC projects

Research project

Diving deep into the biology of STAT3 regulation and -signaling

Rationale and Objectives

For patients with loss-of-function mutations in STAT3 the only currently available cure is hematopoietic stem cell transplantation (HSCT). However, HSCT comes along with a considerable mortality during treatment, especially in adults (expected to be around 20%). Therefore, gene therapy has been suggested as a possible alternative. One option for gene therapy is to inactivate the mutated allele, which however renders the patient STAT3 haplo(in)sufficient. Another approach is to replace both STAT3 alleles with a cassette for STAT3-cDNA expression, eliminating however, alternative STAT3 transcripts.

STAT3 (encoding the signal transducer and activator of transcription-3) represents a paradigm of the highly complex JAK-STAT signal transduction network, which comprises four Janus kinases, seven STAT molecules and additional splice variants. The transcription factor STAT3 is involved in both, the pro-inflammatory IL-6 pathway and the anti-inflammatory IL-10 signaling. Although intensively investigated, the mechanisms by which STAT3 signaling differentiates between pro-and anti-inflammatory signals, remains enigmatic.

STAT3 is the lineage-defining transcription factor for so-called Th17 cells. Hence, reduced STAT3 signaling leads to recurrent infections. In contrast, increased STAT3 signaling leads to autoimmunity and cancer.

In humans, STAT3 is expressed in two isoforms (the alpha and the beta variant) resulting from alternative splicing. The beta version lacks parts of the transactivation (TA) domain of the alpha version, and instead harbors seven unique amino acids. In addition to forming homodimers (and mixed alpha and beta homodimers), STAT3 forms heterodimers with STAT1 and STAT5. However, the conditions under which these heterodimers are being formed and their biological role are still unclear.

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DC4 will focus on addressing the following important topics related to STAT3 signaling biology:

1) study the importance of STAT1/3 splice variant expression on lymphocytes and mononuclear cells with and without stimulation and its impact on gene regulation and downstream gene expression;

2) analyze the impact of various stimuli on the heterodimerformation of STAT molecules and their consequences on gene regulation and downstream gene expression including chromatin accessibility; and

3) design and test a STAT3 gene therapy protocol with an expression cassette replacing the most frequent dominant-negative mutations in the gene STAT3.

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Expected results

Our proposal offers to study in detail the effect of STAT3 haplo(in)sufficiency on distinct immune cells, and explores the importance of STAT3 alternative splicing for the STAT3 biology. Moreover, we will address the enigmatic issue of STAT3 heterodimer formation for STAT3 signaling and will thereby evaluate the best possible strategy to perform gene therapy in STAT3-mutated Job patients. PhD thesis, publication.

Planned secondments

RFHMO (Stepensky/Schejter) to optimise sample preparation and recruitment, m10-m12 (2 months); IJC to perform epigenetic analyses, m13-m15 (2 months); IRB (Geiger) to peform proteomic analyses, m15-m17 EMBL (2 months); EMBL (Zaugg) to learn multi-omic data analysis, m22-m23 (1 month). Finally, the DC will do a secondment at qGenomics to learn cfDNA-seq analyses, m30-31 (1 month).

PhD programme

PhD in Biology, Albert-Ludwig Freiburg University, Germany