S-Phase Kinase Associated Protein 1 (SKP1) is a core component of the SKP1-Cullin-F-box (SCF) E3 ubiquitin ligase complex. It is an adaptor protein, connecting cullin and F-box proteins in the complex. SKP1 mediates the ubiquitination of proteins involved in cell cycle progression, signal transduction and transcription. Previous studies have shown that SKP1 protein is associated with Mitochondrial Dna Depletion Syndrome 13 and Parkinson. To test the effect of SKP1 on cell proliferation, A549 cells were seeded into triplicate wells of 96-well plates and allowed to attach, replaced with various concentrations of recombinant human SKP1. After incubated for 72h, cells were observed by inverted microscope and cell proliferation was measured by Cell Counting Kit-8 (CCK-8). Briefly, 10 µl of CCK-8 solution was added to each well of the plate, then the absorbance at 450 nm was measured using a microplate reader after incubating the plate for 1-4 hours at 37 ℃. Cell viability was assessed by CCK-8 assay after incubation with recombinant human SKP1 for 72h. The result was shown in Figure 1. It was obvious that SKP1 significantly decreased cell viability of A549 cells. The ED50 of recombinant human SKP1 is 0.375 μg/ml.