SK promotes endothelial cell survival. (A) Levels of mRNA for SK as measured by RT-PCR. HUVECs were transfected with siRNA for SK (SK1) or control nonsilencing siRNA (C). The results from 1 experiment representative of 3 performed. (B) Levels of SK activity in 1 experiment of 3 performed and (panel C) cell survival after siRNA treatment (as given in panel A) measured by MTS at time of plating and after 2 days. The absorbance at 490 nM reflects the number of viable cells. □ represents control; ▪, SK. The mean ± SEM of quadruplicate determinations from 1 experiment representative of 3 performed. *P less than 0.05 compared with C. (D) SK activity in HUVECs infected with 1 pfu/cell or 50 pfu/cell of adenoviral supernatant carrying SK or control EV are shown as the composite analysis of 2 separate endothelial cell lines assayed in duplicate and normalized to control. *P less than .001 SK compared with EV at equivalent pfu/cell. Bars represent 95% confidence intervals. (E) The survival of ECs^SK (▪) or ECs^EV (□) as reflected by the optical density at 490 nm in the absence of fetal calf serum (SF) and in the absence of both fetal calf serum and attachment to extracellular matrix (suspension). The SF data represent the pooled data of 43 observations derived from 9 separate experiments, and the suspension data show the pooled data of 10 observations from 2 separate experiments. The cell number at day 2 normalized to day 0 = 1 is given. *P less than .001 compared with ECs^EVat day 0. NS indicates no significant difference compared with ECs^SK at day 0. Bars represent 95% confidence intervals. (F) Cyclin D1 and E expression by Western blot under unstimulated conditions (Nil) and after stimulation with growth factor (GF) for 24 hours. The membrane was counter-blotted with antibody to fetal liver tyrosine kinase 1 (Flt-1) as a loading control.