Sphingosine Kinase Activity and Sphingosine-1 Phosphate Production in Rat Pancreatic Islets and INS-1 Cells

Response to Cytokines

  1. Lucy D. Mastrandrea12,
  2. Shawn M. Sessanna1 and
  3. Suzanne G. Laychock1
  1. 1Department of Pharmacology and Toxicology, The State University of New York, Buffalo, New York
  2. 2Department of Pediatrics, School of Medicine and Biomedical Sciences, The State University of New York, Buffalo, New York
  1. Address correspondence and reprint requests to Suzanne G. Laychock, 102 Farber Hall, The State University of New York at Buffalo, School of Medicine, 3435 Main St., Buffalo, NY 14214. E-mail: laychock{at}buffalo.edu

Abstract

Sphingosine-1 phosphate (S1P) is a bioactive sphingolipid with the potential to mobilize Ca2+, to inhibit apoptosis, and to promote mitogenesis. Sphingosine kinase (SPHK) and S1P were characterized in INS-1 insulinoma cells and isolated rat islets of Langerhans. SPHK activity increased in INS-1 cell homogenates treated with interleukin-1β (IL-1β) or tumor necrosis factor-α (TNF-α), and responses were additive. IL-1β or TNF-α increased islet SPHK activity within 15 min to 1 h; activity remained elevated after 8 h. SPHK2 was the predominant active isoform in INS-1 cells; little or no SPHK1 activity was detected. Cytokines increased endogenous S1P biosynthesis in 32Pi-prelabeled INS-1 cells, and cycloheximide inhibited the response after 8 h, suggesting that protein synthesis mediated the response. There was no [32P]S1P release from cells. Compared with basal values, IL-1β and TNF-α induced increases in SPHK1a mRNA levels relative to 18S ribosomal RNA in INS-1 cells within 1 h; relative SPHK2 mRNA levels were unchanged after cytokine treatment. IL-1β, but not TNF-α, induced relative SPHK1a mRNA expression levels within 1 h in islets, whereas SPHK2 mRNA levels were unchanged. Thus, IL-1β and TNF-α induced an early and sustained increase in SPHK activity in INS-1 cells and isolated islets, suggesting that S1P plays a role in the pathological response of pancreatic β-cells to cytokines.

Footnotes

    • Accepted January 28, 2005.
    • Received August 19, 2004.
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