PLD1
Phospholipase D (PLD) is expressed in
many tissues and stimulated by growth factors and cytokines. However, the role
of PLD in signal transduction is still not well-understood. Human embryonic
kidney (HEK-293) cells exhibit low levels of both PLD1 and PLD2 mRNA, however,
only PLD1 protein was detected by Western blot. When either isoform
of PLD was stably expressed in HEK-293 cells, we observed an increased PLD
activity in a cell-free system and a 12-O-tetradecanoyl-13-phorbol
acetate (TPA)-stimulated increase in PLD activity in intact cells. This system
was then used to elucidate the effects of PLD activity on TPA-stimulated signaling
pathways. Two such pathways, the mitogen-activated
protein kinases (MAPK), extracellular
regulated protein kinase (ERK) and p38 are activated
by growth factors and cellular stress, respectively.
We found that TPA stimulated ERK phosphorylation regardless
of the expression status of PLD. In contrast to ERK kinase,
HEK-293 cells were unable to induce p38 phosphorylation
by TPA stimulation. When HEK-293 cells expressed either PLD1 or PLD2, we
observed elevated p38 phosphorylation in response to
TPA stimulation. The ERK and p38 MAPKs can also
stimulate the expression of both cyclooxygenase-2 (Cox-2) and interleukin-8
(IL-8). We used this system to differentiate the effect of PLD1 or PLD2
activity on the expression of Cox-2 and IL-8. Increased Cox-2 and IL-8
expression was found only in HEK-293 cells expressing PLD1. These data identify
a novel role for the PLD1 isoform in the induction of
gene expression and provide new insight into the differential role of PLD1 and
PLD2 in cells.
PMID: 14984736 [PubMed - in process]