CD315, also known as prostaglandin F2 receptor negative regulator, is an approximately 135 kDa transmembrane glycoprotein, which associates with actin cytoskeleton, and with CD9 and CD81, but not with other tetraspanins. It seems to be involved in regulation of cell polarity and motility. CD315 is expressed mainly by keratinocytes, activated monocytes, and a subset of B cells, but it can be also used for distinguishing between strongly positive colon cancer and fibrosarcoma cells, and their negative normal cell counterparts.