Phosphorylation of serine 523 on XXXX in @entity1 B lymphocytes.

@entity1 @entity1437 @entity1421 @entity4352 @entity8624 @entity1892 @entity48943 @entity855 @entity7410
The key enzyme in @entity4352 (LT) biosynthesis is @entity1437 (5-LO), which is expressed in myeloid cells and in B lymphocytes. There are three phosphorylation sites on 5-LO (Ser271, Ser523 and Ser663). Protein kinase A (PKA) phosphorylates 5-LO on Ser523. In this report, we demonstrate by immunoblotting that native 5-LO in @entity1892 ( @entity1892 ) cells (Granta519, JEKO1, and @entity48943 ) and in primary chronic @entity8624 cells (B-CLL) is phosphorylated on Ser523. In contrast, we could not detect phosphorylation of 5-LO on Ser523 in @entity1 granulocytes or monocytes. Phosphorylated 5-LO was purified from @entity48943 cells, using an @entity855 -agarose column, and the partially purified enzyme could be dephosphorylated with alkaline phosphatase. Incubation of @entity48943 cells with @entity7410 or @entity1421 stimulated phosphorylation at Ser523. Furthermore, FLAG-5LO was expressed in @entity48943 cells, and the cells were cultivated in the presence of @entity7410 . The 5-LO protein from these cells was immunoprecipitated, first with anti-FLAG, followed by anti-pSer523-5-LO. The presence of 5-LO protein in the final precipitate further supported the finding that the protein recognized by the pSer523 antibody was 5-LO. Taken together, this study shows that 5-LO in B cells is phosphorylated on Ser523 and demonstrates for the first time a chemical difference between 5-LO in myeloid cells and B cells.
