AnxA9

Annexin A9 (ANXA9) is a member of the annexin protein family and participates in membrane-associated biological processes through phospholipid interactions, although it differs structurally from most annexins because all four conserved type II calcium-binding sites contain substitutions that abolish canonical calcium coordination^[1][2]. Mechanistically, this structural divergence results in atypical biochemical behavior, as ANXA9 exhibits phospholipid binding only at relatively high calcium concentrations and its membrane association is not regulated in the same manner as classical annexins^[2]. Consistent with a specialized membrane-related function, ANXA9 interacts with periplakin and has been implicated in membrane-cytoskeleton organization and epidermal differentiation processes^[3][4]. In disease-related studies, increased ANXA9 expression has been associated with tumor progression, invasion, and metastatic behavior in several cancer types, particularly colorectal cancer, where expression levels correlate with invasion depth and lymphatic metastasis^[5][6]. Experimental evidence further indicates that ANXA9 can promote colorectal cancer cell proliferation through regulation of Wnt signaling, supporting a functional role in cancer-associated signaling networks^[6]. Compared with related annexin isoforms that retain conserved calcium-binding activity, ANXA9 represents a divergent annexin family member with reduced calcium responsiveness but preserved membrane-binding capability, highlighting distinct biological functions within the annexin superfamily^[1][2]. Currently, no widely established selective ANXA9 agonists or inhibitors have been reported, and most studies employ gene-expression analyses or genetic manipulation approaches to investigate its biological roles and disease relevance^[5][6].

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