Functional interaction between Sp1 and c‐Jun in phorbol 12‐myristate 13‐acetate‐induced gene expression of cytosolic phospholipase A2α

The functional role of the interaction between c‐Jun and simian virus 40 promoter factor 1 (Sp1) in 12‐myristate 13‐acetate (PMA)‐induced expression of cytosolic phospholipase A 2 α (cPLA 2 α) gene in A549 human lung adenocarcinoma cell was studied. PMA increased the expression of cPLA 2 α in a time‐dependent manner. The effect of PMA on the promoter activation of cPLA 2 α gene was analyzed by using the luciferase fusion vectors. PMA and overexpression of c‐Jun induced the promoter activity of cPLA 2 α in a dose‐ and time‐dependent manner. Transient transfection with series of 5′‐deleted constructs showed that the 5′‐flanking region spanning from −53 to −17 bp from translation starting site played an important role for PMA response. Site‐directed mutagenesis indicated that two non‐classical Sp1 binding sequences residing at −51 to −42 bp and −33 to −24 bp were responsible for the PMA and c‐Jun in activation of human cPLA 2 α gene expression. Furthermore, coimmunoprecipitation and DNA affinity precipitation assay experiments indicated that PMA stimulated interaction between c‐Jun and Sp1 in a time‐dependent manner and binding of c‐Jun/Sp1 to promoter. These results indicate that the interaction between c‐Jun and Sp1 induced by PMA cooperatively activated expression of cPLA 2 α gene.