Annexin A1 (ANXA1; formerly called macrocortin, renocortin, lipomodulin and lipocortin 1) is a 37 kDa protein member of an annexin superfamily which has a binding or annexing property to acidic phospholipid in a calcium dependent manner (Gerk & Moss, 2002). This molecule was independently discovered by four groups of researchers (Flower & Blackwell, 1979; Di Rosa & Persico, 1979; Russo-Marie et al, 1979 and Hirata et al, 1980). The gene encoding human ANXA1 is located on chromosome 19q24 and was first cloned by Wallner and co-workers in 1986. This protein plays an important role in the neuroendocrine system (Bugkingham et al, 2006), cell growth, exocytosis and endocytosis (Gerke and Moss, 2002), apoptosis (Solito et al, 2003), phagocytsis (Arur et al, 2003) and T cell activation and differentiation (D’Acquisto et al, 2007). Structurally, the core C-terminal domain of ANXA1 contains four repeated sequences of 70 amino acids which are similar to other annexin family members and a unique N-terminal domain which comprise of 44 amino acids responsible for glycosylation, acetylation, proteolysis and protein kinase C and tyrosine kinase phosphorylation (John et al, 2004). In rat peritoneal leucocytes, there are three pools of ANXA1, including cytoplasm, intramembrane and on the outer surface of the plasma membrane.
It is well accepted that ANXA1 is not expressed in adult normal neurons. ANXA1-immunoreactive microglial cells were found throughout the brain tissue and strongly expressed in striatum, hypothalamus, hippocampus and cortex (Savchenko et al, 2000). ANXA1–immunoreactive amoeboid microglia were present within the astrocytic envelope of neurons adjacent to or within glial scars in SNc of PD in a post mortem study (Knott et al, 2000). Interestingly, it is reported that cultured microglia secreted ANXA1 (Young et al, 1999).
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