Mrc1 is a conserved checkpoint mediator protein that transduces the replication stress signal to the downstream effector kinase. Mrc1 and its vertebrate homologue Claspin serve as a mediator for replication stress checkpoint signaling, receiving the signal from Mec1/Rad3/ATR sensor kinase and transmitting it to the effector Rad53/Cds1/Chk1 kinase. The loss of mrc1 checkpoint activity results in the aberrant activation of late/dormant origins in the presence of hydroxyurea. Tumor-associated macrophages (TAMs) expressing the multi-ligand endocytic receptor mannose receptor (CD206/MRC1) contribute to tumor immunosuppression, angiogenesis, metastasis, and relapse.