Extracellular nucleotides induce migration of renal mesangial cells by upregulating sphingosine kinase-1 expression and activity.
Background and purpose:Extracellular nucleotides act as potent mitogens for renal mesangial cells (MC). In this study we determined whether extracellular nucleotides trigger additional responses in MCs and the mechanisms involved.Experimental approach:MC migration was measured after nucleotide stimulation in an adapted Boyden-chamber. Sphingosine kinase-1 ( SK-1) protein expression was detected by Western blot analysis and mRNA expression quantified by real-time PCR. SK activity was measured by an in vitro kinase assay using sphingosine as substrate.Key results:Nucleotide stimulation caused biphasic activation of SK-1, but not SK-2. The first peak occurred after minutes of stimulation and was followed by a second delayed peak after 4-24 h of stimulation. The delayed activation of SK-1 is due to increased SK-1 mRNA steady-state levels and de novo synthesis of SK-1 protein, and depends on PKC and the classical MAPK cascade. To see whether nucleotide-stimulated cell responses require SK-1, we selectively depleted SK-1 from cells by using small-interference RNA (siRNA). MC migration is highly stimulated by ATP and UTP; this is mimicked by exogenously added S1P. Depletion of SK-1 by siRNA drastically reduced the effect of ATP and UTP on cell migration but not on cell proliferation. Furthermore, MCs isolated from SK-1-deficient mice were completely devoid of nucleotide-induced migration.Conclusions and implications:These data show that extracellular nucleotides besides being mitogenic also trigger MC migration and this cell response critically requires SK-1 activity. Thus, pharmacological intervention of SK-1 may have impacts on situations where MC migration is important such as during inflammatory kidney diseases.British Journal of Pharmacology (2007) 150, 271-280. doi:10.1038/sj.bjp.0706983; published online 2 January 2007.[1]References
- Extracellular nucleotides induce migration of renal mesangial cells by upregulating sphingosine kinase-1 expression and activity. Klawitter, S., Hofmann, L.P., Pfeilschifter, J., Huwiler, A. Br. J. Pharmacol. (2007) [Pubmed]
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