Mutation-Driven S100A8 Overexpression Confers Aberrant Phenotypes in Type 1 CALR-Mutated MPN

Area of Science:

• Molecular Biology
• Hematology
• Oncology

Background:

• Myeloproliferative neoplasms (MPN) are driven by mutations in genes like Calreticulin (CALR).
• Specific CALR exon 9 mutations, such as type 1 (CALR^DEL) and type 2 (CALR^INS), are most common.
• The reasons for diverse clinical phenotypes despite shared MPN pathobiology remain unclear.

Purpose of the Study:

• To investigate the molecular mechanisms underlying differential gene expression in MPN based on specific CALR mutations.
• To identify specific genes and pathways affected by CALR^DEL versus CALR^INS mutations.
• To explore the functional and clinical relevance of identified molecular differences.

Main Methods:

• RNA sequencing and protein/mRNA level validation in MPN model cells.
• Luciferase reporter assays and inhibitor treatments to study gene regulation.
• Pyrosequencing for epigenetic analysis of promoter regions.
• Functional assays assessing cellular proliferation and apoptosis.
• Clinical validation of gene expression in patient cohorts.

Main Results:

• S100A8 was specifically enriched in CALR^DEL MPN model cells, but not in CALR^INS cells.
• STAT3 was identified as a regulator of S100A8 expression, with hypomethylation in the CALR^DEL promoter region.
• S100A8 contributed to accelerated proliferation and reduced apoptosis in CALR^DEL cells.
• Clinical data showed higher S100A8 expression in CALR^DEL MPN patients, correlating with less prominent thrombocytosis.

Conclusions:

• Distinct CALR mutations differentially regulate specific gene expression, such as S100A8.
• Epigenetic alterations in the S100A8 promoter may contribute to divergent S100A8 levels.
• S100A8 plays a functional role in MPN pathogenesis and influences clinical presentation.