ETA-1, or Secreted phosphoprotein 1, is a human gene encoded by SPP1. It may also be known as: Osteopontin; Nephropontin; SPP-1; Urinary stone protein; Uropontin; Bone sialoprotein 1; early T-lymphocyte activation 1; BSPI; OPN. The encoded protein has an amino acid length of 314 and a mass of 35.4 kDa. ETA-1 is a member of the Osteopontin family. Homologs of this gene exist in other organisms, including: Mouse.