A-kinase anchor protein 4 (AKAP4)

A-kinase anchor protein 4 (AKAP4) is a scaffold protein of the AKAP family that binds and anchors protein kinase A (PKA) to the fibrous sheath of the sperm flagellum, orchestrating compartmentalized cAMP-dependent and cAMP-independent signaling essential for sperm motility and male fertility. AKAP4 is processed from a precursor (proAKAP4) during sperm maturation and is highly conserved among mammals. Loss of AKAP4 disrupts fibrous sheath formation and leads to male infertility due to immotile sperm. As a member of the cancer/testis antigen family, AKAP4 is aberrantly expressed in several human cancers (including colon, breast, cervical, lung, and multiple myeloma), making it a candidate biomarker and immunotherapeutic target. AKAP4 is not a receptor, enzyme, ion channel, or transporter, but a molecular scaffold coordinating interactions mainly between PKA, PKC, ERK1/2, and other kinases; it plays important roles in both spermatogenesis and cancer cell biology.

Other names

AKAP4AKAP82AKAP-4AKAP 82hAKAP82HIPRKA4p82Fsc1CT99Major sperm fibrous sheath proteinCancer/testis antigen 99Epididymis secretory sperm binding proteinProtein kinase A anchoring protein 4Testis-specific gene HI