PKC- and PI3K-dependent but ERK-independent proliferation of murine splenic B cells stimulated by chondroitin sulfate B

High molecular weight polyanions such as dextran sulfate are known to be weak polyclonal activators of murine B cells, but the molecular mechanism of their mitogenic activitiy is not fully elucidated. Although chondroitin sulfate A (CSA), B (CSB) and C (CSC) are highly charged polyanions, little is known about their effects on the proliferation of B cells. In this study, we demonstrated that CSB stimulated proliferation of murine B cells as markedly as did anti-IgM antibody, more markedly than did dextran sulfate and much more markedly than did CSA, CSC, heparin and hyaluronic acid. CSB caused translocation of protein kinase C (PKC) isoform beta from cytosol to membrane fractions and increased phosphorylation of Akt but not phosphorylation of extracellular signal-regulated kinase (ERK) of B cells. CSB-induced B cell proliferation was almost completely blocked by either the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 or the PKC inhibitor GF109203X but was not significantly inhibited by the ERK kinase inhibitor PD98059. The mitogenic effect of anti-IgM was significantly inhibited by all the three inhibitors, while the mitogenic effect of LPS was inhibited only by LY294002. These findings indicate that CSB stimulated proliferation of murine B cells more markedly than did dextran sulfate and suggest that PKC and PI3K are crucial but that ERK is less important for the mitogenic activity of CSB, the signaling pathways of which may be at least partly distinct from those of anti-IgM and LPS.