Described is a novel family of cell surface serpentine transmembrane
antigens. Two of the proteins in this family are exclusively or
predominantly expressed in the prostate, as well as in prostate cancer,
and thus members of this family have been termed "STEAP" (Six
Transmembrane Epithelial Antigen of the Prostate). Four particular human
STEAP's are described and characterized herein. The human STEAP's exhibit
a high degree of structural conservation among them but show no
significant structural homology to any known human proteins. The
prototype member of the STEAP family, STEAP-1, appears to be a type IIIa
membrane protein expressed predominantly in prostate cells in normal
human tissues. Structurally, STEAP-1 is a 339 amino acid protein
characterized by a molecular topology of six transmembrane domains and
intracellular N- and C-termini, suggesting that it folds in a
"serpentine" manner into three extracellular and two intracellular loops.
STEAP-1 protein expression is maintained at high levels across various
stages of prostate cancer. Moreover, STEAP-1 is highly over-expressed in
certain other human cancers.