Enhancement of sphingosine kinase 1 catalytic activity by deletion of 21 amino acids from the COOH-terminus.

Sphingosine kinase 1 (SphK1) responds to a variety of growth factor signals by increasing catalytic activity as it translocates to the plasma membrane (PM). Several studies have identified amino acids residues involved in translocation yet how SphK1 increases its catalytic activity remains to be elucidated. Herein, we report that deletion of 21 amino acids from the COOH-terminus of SphK1 (1-363) results in increased catalytic activity relative to wild-type SphK1 (1-384) which is independent of the phosphorylation state of Serine 225 and PMA stimulation. Importantly, HEK293 cells stably expressing the 1-363 protein exhibit enhanced cell growth under serum-deprived cell culture conditions. Together the evidence indicates that the COOH-terminal region of SphK1 encompasses a structural element that is necessary for the increase in catalytic activity in response to PMA treatment and that its deletion renders SphK1 constitutively active with respect to PMA treatment.