The CUB1 antibody recognizes CD318 also known as CDCP1, CUB domain containing protein 1, and SIMA135. CD318 is a transmembrane protein containing three CUB domains with a predicted molecular weight of approximately 93 kD. Alternately spliced isoforms have also been reported. CD318 is a marker for immature hematopoietic progenitor cell subsets and is also expressed in mesenchymal stem cells and neural progenitor cell populations. This marker is also widely distributed in a variety of cell types including keratinocytes, skeletal muscle, colon, kidney, lung, small intestine. CD318 is overexpressed in colon and lung tumors and expression level has been shown to correlate with metastatic ability of carcinomas. CD318 interacts with plasminogen, matriptase, and c-Src (phosphorylates residue Y734). The function of CD318 is not well understood although it is thought to be involved in early hematopoiesis. The CUB1 antibody has been shown to be useful for flow cytometry.