JAK2V617F promotes replication fork stalling with disease-restricted impairment of the intra-S checkpoint response

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Cancers arise from accumulated genetic lesions, but early-stage cellular consequences of driver mutations are not fully understood.
• The JAK2 V617F mutation is an early event in myeloproliferative neoplasms (MPNs), offering a model for studying early tumorigenesis.
• JAK2V617F impacts DNA replication and activates the intra-S checkpoint via PI3K signaling.

Purpose of the Study:

• To investigate the cellular consequences of the JAK2V617F mutation in early tumorigenesis.
• To analyze replication fork progression and intra-S checkpoint activation in MPN erythroblasts.
• To explore disease-specific differences in DNA damage response in polycythemia vera (PV) and essential thrombocythemia (ET).

Main Methods:

• Analysis of clonally derived JAK2V617F-positive erythroblasts from MPN patients.
• Assessment of replication fork progression and replication protein A (RPA) foci.
• Evaluation of intra-S checkpoint response and gamma-H2Ax (γ-H2Ax) double-strand breaks following p53 inhibition.

Main Results:

• JAK2V617F expression impairs replication fork progression in primary MPN cells.
• Intra-S checkpoint response was impaired in polycythemia vera (PV) erythroblasts but not in essential thrombocythemia (ET) erythroblasts.
• Inhibition of p53 in PV erythroblasts led to increased γ-H2Ax foci compared to ET erythroblasts, indicating higher DNA damage.

Conclusions:

• Oncogene-induced replication stress occurs in primary MPN cells.
• Disease-specific differences in intra-S checkpoint activation exist within MPNs.
• Defective intra-S checkpoint function in PV, coupled with attenuated p53 signaling, may increase DNA damage and influence clonal evolution.