SPHINGOSINE 1-PHOSPHATE AND SPHINGOSINE KINASE: NEW PLAYERS IN CALCIUM REGULATED EXOCYTOSIS

SUHAIMAN, LAILA; DE BLAS, GERARDO A; OBEID, LINA M; DARSZON, ALBERTO; MAYORGA, LUIS S; BELMONTE, SILVIA A

Holderness, NH, USA.

Conferencia; Gordon Research Conference in Fertilization & Activation of Development; 2009

GRC

SPHINGOSINE 1-PHOSPHATE AND SPHINGOSINE KINASE 1: NEW PLAYERS IN CALCIUM REGULATED EXOCYTOSISLaila Suhaiman1, Gerardo A. De Blas2, Lina M. Obeid3, Alberto Darszon2, Luis S. Mayorga1, and Silvia A. Belmonte1Laboratorio de Biologia Celular y Molecular, Instituto de Histologia y Embriologia (IHEM-CONICET), Facultad de Ciencias Medicas, CC56, Universidad Nacional de Cuyo, 5500, Mendoza, Argentina1; Departamento de Genetica del Desarrollo y Fisiologia Molecular, Instituto de Biotecnologia, Universidad Nacional Autonoma de Mexico, Cuernavaca, Morelos, Mexico2 and, Department of Medicine and Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29425, USA3.e-mail: sbelmont@fcm.uncu.edu.arRegulated secretion is a central issue for the specific function of many cells; for instance, mammalian sperm acrosomal exocytosis is essential for egg fertilization. Sphingosine 1-phosphate is a bioactive sphingolipid that regulates crucial physiological processes. Here we report that this lipid triggers acrosomal exocytosis in human sperm by a mechanism involving a Gi-coupled receptor. Real time imaging showed a remarkable increase of cytosolic calcium upon activation with sphingosine 1-phosphate and pharmacological experiments indicate that the process requires extracellular Ca2+ influx through voltage and store operated calcium channels and efflux from intracellular stores through IP3-sensitive Ca2+ channels. Sphingosine 1-phosphate-induced exocytosis requires phospholipase C, protein kinase A, and protein kinase C activation. We investigated possible sources of the lipid. Western blot indicates that sphingosine kinase 1 is present in spermatozoa. Indirect immunofluorescence showed that phorbol ester-a potent protein kinase C activator that can also trigger acrosomal exocytosis redistributes sphingosine kinase 1 to the acrosomal region. Functional assays indicate that phorbol ester-induced exocytosis depends on the activation of sphingosine kinase 1 (SK). Furthermore, incorporation of 32P to sphingosine demonstrates that cells treated with the phorbol ester increase their SK activity rendering sphingosine 1-phosphate. We present here the first evidence indicating that human spermatozoa produces the sphingolipid when challenged with an exocytic stimulus. These observations point to a new role of sphingosine 1-phosphate in a signaling cascade that facilitates acrosome reaction providing some clues about novel lipid molecules involved in exocytosis.