Loss of S-phase was consistently associated with an increase in the percentage of cells in G1 but no change in the percentage of cells in G2/M. Thus, we conclude that the proliferation defects in HUVECs R428 Axl inhibitor following YAP knockdown are the result of significant blockages in the G1 and/or S phases of the cell cycle. DAVID bioinformatics resource database and gene set enrichment analysis revealed that the loss of YAP negatively affected the expression of multiple genes critical to cell cycle, DNA replication and DNA damage repair processes. Specifically, we found that the expression of several genes involved in replication origin ICI 182780 function and homologous recombination were negatively affected in YAP-KD mutants. Additional genes critical to origin licensing and firing as well as homologous recombination were identified as YAP targets when the fold change threshold was lowered to 1.2 fold. We confirmed that many of these targets were down-regulated at the transcript level by qPCR. Furthermore, western blotting with commercially available antibodies for two of the replication origin function factors also showed decreased expression of these proteins in YAP-depleted cells. Thus, the HUVEC proliferation defects observed following YAP knockdown are associated with decreased expression of genes involved in DNA replication origin function and DNA repair. Consistent with prior studies with mesothelioma cells, we found that YAP is required for cell cycle progression in human primary endothelial cells. BrdU analysis of YAP-KD HUVECs suggested that YAP is required during S-phase, and two sets of APH arrest experiments were conducted to distinguish the role of YAP in this process. The short-term APH arrest assessed the ability of YAP-KD mutants to reinitiate stalled S-phase. As both control and mutants groups recovered from the arrest with similar kinetics, we conclude that HUVECs can progress through S-phase independent of YAP. By contrast, YAP-KD cells were unable to begin S-phase following long-term APH block. Taken together, these APH synchronization experiments demonstrate that YAP controls cell proliferation at least partly by facilitating a G1-to- S transition. It is worth noting the variety and context-dependency of Hippo pathway target genes that have been reported. Muramatsu et al. identified BIRC5 and CDKN2A/p21 as two significant targets of YAP that are responsible for modulating the survival and proliferation in KYSE170 cells. In addition, the Hippo pathway target CTGF may also function as a driver of YAPinduced colon cell tumorigenesis.