EF-hand motif found in phosphoinositide phospholipase C delta 4 (PI-PLC-delta4)
PI-PLC-delta4, also termed 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase delta-4 (PLCD4), or phospholipase C-delta-4 (PLC-delta-4), is expressed in various tissues with the highest levels detected selectively in the brain, skeletal muscle, testis and kidney. It plays a significant role in cell growth, cell proliferation, tumorigenesis, and in an early stage of fertilization. PI-PLC-delta4 may function as a key enzyme in the regulation of PtdIns(4,5)P2 levels and Ca2+ metabolism in nuclei in response to growth factors, and its expression may be partially regulated by an increase in cytoplasmic Ca2+. Moreover, PI-PLC-delta4 binds glutamate receptor-interacting protein1 (GRIP1) in testis and is required for calcium mobilization essential for the zona pellucida-induced acrosome reaction in sperm. Overexpression or dysregulated expression of PLCdelta4 may initiate oncogenesis in certain tissues through upregulating erbB1/2 expression, extracellular signal-regulated kinase (ERK) signaling pathway, and proliferation in MCF-7 cells. PI-PLC-delta4 contains an N-terminal pleckstrin homology (PH) domain, four atypical EF-hand motifs, a PLC catalytic core domain, and a C-terminal C2 domain. The PLC catalytic core domain is a TIM barrel with two highly conserved regions (X and Y) split by a highly degenerate linker sequence. Unlike PI-PLC-delta 1 and 3, a putative nuclear export sequence (NES) located in the EF-hand domain, which may be responsible transporting PI-PLC-delta1 and 3 from the cell nucleus, is not present in PI-PLC-delta4.