Received for publication August 11, 2004.
Revised November 9, 2004.
Accepted for publication November 9, 2004.

PHOSPHOLIPASE D SIGNALING AND EXTRACELLULAR SIGNAL-REGULATED KINASE (ERK)-1 AND 2 PHOSPHORYLATION (ACTIVATION) ARE REQUIRED FOR MAXIMAL PHORBOL ESTER-INDUCED TRANSGLUTAMINASE ACTIVITY, A MARKER OF KERATINOCYTE DIFFERENTIATION

Abstract

Protein kinase C (PKC)-activating 12-O-tetradecanoylphorbol 13-acetate (TPA) stimulates phospholipase D (PLD) activity in primary mouse epidermal keratinocytes. PLD catalyzes the hydrolysis of phosphatidylcholine to yield phosphatidic acid (PA), which can be dephosphorylated to produce PKC-activating diacylglycerol. In the presence of small amounts of a primary alcohol, PLD can instead produce novel phosphatidylalcohols at the expense of PA and diacylglycerol. Here we have demonstrated that inhibiting PLD signal generation with 1-butanol reduced TPA-stimulated transglutaminase activity, a marker of keratinocyte differentiation. On the other hand, the structurally related tertiary alcohol, tert-butanol, which cannot be utilized by PLD, had no effect on TPA-induced transglutaminase activity. Since TPA activates all conventional and novel PKC isoforms directly, yet cannot overcome 1-butanol-mediated inhibition, this result suggests that PLD mediates its effects on transglutaminase activity (and keratinocyte differentiation) through an effector enzyme system distinct from the conventional or novel PKC isoenzymes. Data in the literature suggest that PA can recruit Raf-1 to the membrane, where it can be activated and initiate the mitogen-activated protein kinase cascade that culminates in activation of extracellular signal-regulated kinase-1 and -2 (ERK-1/2). Indeed, we found that inhibition of ERK-1/2 phosphorylation (activation) inhibited TPA-induced transglutaminase activity. However, inhibition of PLD-mediated signal generation had only a small effect on TPA-elicited ERK-1/2 phosphorylation (activation) while inhibition of ERK-1/2 did not affect PLD activation, suggesting that these two pathways likely operate largely in parallel. Thus, our results suggest the independent involvement of the PLD and ERK-1/2 pathways in mediating transglutaminase activity and keratinocyte differentiation.

Key words: 12-O-tetradecanoylphorbol 13-acetate, diacylglycerol, mitogen-activated protein kinase, phosphatidic acid, skin, tumorigenesis

This article has been cited by other articles:

				P. Bayo, A. Sanchis, A. Bravo, J. L. Cascallana, K. Buder, J. Tuckermann, G. Schutz, and P. Perez Glucocorticoid Receptor Is Required for Skin Barrier Competence Endocrinology, March 1, 2008; 149(3): 1377 - 1388. [Abstract] [Full Text] [PDF]

				S. Krisanaprakornkit, P. Chotjumlong, P. Kongtawelert, and V. Reutrakul Involvement of phospholipase D in regulating expression of anti-microbial peptide human -defensin-2 Int. Immunol., January 1, 2008; 20(1): 21 - 29. [Abstract] [Full Text] [PDF]

				K. J. Fogle, A. K. Lyashchenko, H. K. Turbendian, and G. R. Tibbs HCN Pacemaker Channel Activation Is Controlled by Acidic Lipids Downstream of Diacylglycerol Kinase and Phospholipase A2 J. Neurosci., March 14, 2007; 27(11): 2802 - 2814. [Abstract] [Full Text] [PDF]

				C. Lee, H.-K. Lim, J. Sakong, Y.-S. Lee, J.-R. Kim, and S.-H. Baek Janus Kinase-Signal Transducer and Activator of Transcription Mediates Phosphatidic Acid-Induced Interleukin (IL)-1beta and IL-6 Production Mol. Pharmacol., March 1, 2006; 69(3): 1041 - 1047. [Abstract] [Full Text] [PDF]