Annexin A1 (ANXA1)

Annexin A1 is a human protein encoded by the ANXA1 gene. Annexin I belongs to a family of Ca²⁺-dependent phospholipid-binding proteins that have a molecular weight of approximately 35,000 to 40,000 and are preferentially located on the cytosolic face of the plasma membrane. Annexin I protein has an apparent relative molecular mass of 40 kDa, with phospholipase A2 inhibitory activity.

The gene for annexin A1 (ANXA1) is upregulated in hairy cell leukemia. ANXA1 protein expression is specific to hairy cell leukemia. Detection of ANXA1 (by immunocytochemical means) reportedly provides a simple, highly-sensitive and specific assay for the diagnosis of hairy cell leukemia.