SPHINGOSINE 1-PHOSPHATE AND SPHINGOSINE KINASE 1 ARE INVOLVED IN A NOVEL SIGNALING PATHWAY LEADING TO HUMAN SPERM ACROSOMAL EXOCYTOSIS.

SUHAIMAN L; DE BLAS GA; OBEID L; DARSZON A; MAYORGA LS; BELMONTE SA

Charleston Carolina del Sur. USA.

Congreso; 5TH International Charleston Ceramide Conference.; 2009

International Charleston Ceramide Conference

Regulated 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 S1P and pharmacological experiments indicate that the process requires extracellular calcium influx through voltage and store operated calcium channels and efflux from intracellular stores through IP3-sensitive calcium 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. These observations point to a new role of sphingosine 1-phosphate in a signaling cascade that facilitates acrosome reaction providing some clues about new molecules involved in exocytosis.