STAT5B leukemic mutations, altering SH2 tyrosine 665, have opposing impacts on immune gene programs

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Signal transducer and activator of transcription 5B (STAT5B) is crucial for lymphocyte function.
• Mutations in STAT5B are implicated in human T cell leukemias.
• Understanding the functional impact of specific STAT5B variants is essential for disease insight.

Purpose of the Study:

• To investigate the functional consequences of two STAT5B mutations (Y665F and Y665H) found in human T cell leukemias.
• To determine the pathogenicity and cellular effects of these STAT5B variants using computational and experimental models.
• To elucidate the mechanistic roles of STAT5B mutations in T cell populations and their potential link to hematopoietic malignancies.

Main Methods:

• In silico modeling to predict the energetic effects of STAT5B mutations on homodimerization.
• In vitro studies using primary T cells to assess STAT5B gain- and loss-of-function.
• In vivo studies involving knock-in mice to evaluate the impact of STAT5B mutations on T cell populations and ratios.
• Analysis of STAT5 phosphorylation, DNA binding, and transcriptional activity following cytokine activation.

Main Results:

• STAT5B^Y665F demonstrated a gain-of-function, leading to increased CD8+ effector/memory and CD4+ regulatory T cells in mice, altering CD8+/CD4+ ratios.
• STAT5B^Y665H exhibited a loss-of-function, resulting in diminished CD8+ effector/memory and CD4+ regulatory T cells.
• The STAT5B^Y665F variant showed enhanced STAT5 phosphorylation, DNA binding, and transcriptional activity compared to wild-type STAT5.
• The STAT5B^Y665H variant functioned similarly to a null allele.

Conclusions:

• Combining in silico and in vivo approaches deepens the understanding of disease-associated genetic variants.
• The study identified specific structural determinants responsible for altered STAT5B function.
• A gain-of-function STAT5B variant (Y665F) was identified that impacts T cell populations without directly inducing hematopoietic malignancy.