Regulation of the expression of group IIA and group V secretory phospholipases A(2) in rat mesangial cells.

Rat mesangial cells synthesize and secrete a secretory phospholipase A(2) upon stimulation of the cells with cytokines, like IL-1beta and TNF and with cAMP elevating agents like forskolin. This enzyme was previously characterized to belong to group IIA sPLA(2). The discovery of several other low molecular weight phospholipases, like group IIC in murine testis and group V in human and rat heart, prompted investigations on the presence of group IIC and group V sPLA(2) in rat mesangial cells. This was done by isolating the RNA from stimulated cells and performing RT-PCR, using primers specific for group IIC and V sPLA(2). The results indicate that rat mesangial cells upon stimulation express next to group IIA also group V sPLA(2). No indications were obtained for the expression of group IIC sPLA(2). The regulation of the expression of group V sPLA(2) at the mRNA level was further investigated by examining the time-dependent expression, the influence of dexamethasone and the signaling route of the IL-1beta stimulation. The results show that the IL-1beta induced expression of group V sPLA(2) mRNA was time dependent and, similar to that of group IIA sPLA(2) mRNA, involves activation of NF-kappaB. However, in contrast to the group IIA sPLA(2), the expression of group V sPLA(2) was not influenced by the presence of dexamethasone. The expression of both phospholipases was also examined at the protein level in stimulated mesangial cells. Western blot analysis shows that stimulated mesangial cells synthesize both group IIA and group V sPLA(2) protein but the expression of group V is lower compared to that of group IIA sPLA(2). In addition, the extent of secretion into the medium appears to be considerably higher for group IIA than for group V sPLA(2).