Tyrosine phosphorylation of CARM1 promotes its enzymatic activity and alters its target specificity

Area of Science:

• Epigenetics
• Molecular Biology
• Cancer Biology

Background:

• Histone phosphorylation is a key epigenetic mechanism in tyrosine kinase signaling.
• Protein arginine methyltransferases (PRMTs) enzymatic activity is regulated by phosphorylation.
• Coactivator-associated arginine methyltransferase 1 (CARM1) is a target in hematologic malignancies.

Purpose of the Study:

• To investigate the effect of Janus kinase 2 (JAK2) V617F mutation on CARM1 phosphorylation and activity.
• To determine the impact of CARM1 phosphorylation on its substrate specificity and cellular function.
• To evaluate the therapeutic potential of targeting JAK2 and CARM1 in acute myeloid leukemia (AML).

Main Methods:

• Site-directed mutagenesis to create non-phosphorylatable CARM1 mutants.
• In vitro methyltransferase assays to assess CARM1 activity and substrate specificity.
• Cell-based assays to evaluate cell-cycle progression, apoptosis, and gene expression.
• Inhibition studies in AML cell lines with JAK2 and CARM1 inhibitors.

Main Results:

• JAK2-V617F phosphorylates CARM1 at Y149 and Y334, increasing its methyltransferase activity and altering substrate specificity.
• Phospho-CARM1 specifically methylates the RUNX1 transcription factor, unlike non-phosphorylatable CARM1.
• Cells with non-phosphorylatable CARM1 exhibit impaired cell-cycle progression, increased apoptosis, and reduced expression of G2/M and anti-apoptotic genes.
• Dual targeting of JAK2 and CARM1 is more effective than monotherapy in AML cells expressing phospho-CARM1.

Conclusions:

• Phosphorylation of CARM1 by hyperactivated JAK2 regulates its methyltransferase activity and substrate selection.
• CARM1 phosphorylation is essential for the proliferation of malignant myeloid cells.
• Dual JAK2 and CARM1 inhibition represents a promising therapeutic strategy for AML.