Growth arrest-specific 6, also known as GAS6, is a gamma-carboxyglutamic acid (Gla) domain-containing protein thought to be involved in the stimulation of cell proliferation. It has been reported that both PC-3 and DU 145 human prostate cancer cell lines are stimulated to proliferate by Gas6, however, this proliferative response strictly correlates with the expression of the Axl receptor, being higher in DU 145 cells. To test the proliferative effect of Gas6, DU 145 cells were seeded into triplicate wells of 96-well plates at a density of 2,000 cells/well and allowed to attach overnight, then the medium was replaced with serum-free standard DMEM prior to the addition of various concentrations of GAS6. After incubated for 72h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10µL of CCK-8 solution was added to each well of the plate, then measure the absorbance at 450nm using a microplate reader after incubating the plate for 1-4 hours at 37oC.
Cell proliferation of DU145 cells after incubation with GAS6 for 72h observed by inverted microscope was shown in Figure 1.

The dose-effect curve of GAS6 was shown in Figure 2. It was obvious that GAS6 significantly promoted cell proliferation of DU145 cells. The ED50 for this effect is typically 0.77~38.08ng/mL.