STEAP1 blocking peptide

The six-transmembrane epithelial antigen of prostate (STEAP) protein was identified in advanced prostate cancer and is up-regulated in multiple cancer cell lines, including prostate, bladder, colon, ovarian, and Ewing sarcoma. STEAP1 was described as a suitable antigen for T-cell-based or antibody-based immunotherapy. We have investigated the expression of STEAP1 in 40 human tumor types - brain, epithelial, lymphoid and in their normal tissue counterparts using publicly available gene expression data, including the Oncomine Cancer Microarray database. STEAP1 was found significantly overexpressed in 11 cancers. In addition, high STEAP1 expression was associated with poor overall survival in colorectal cancer, diffuse large B cell lymphoma, acute myeloid leukemia and multiple myeloma. Taken together, these data suggest that STEAP1 is a potential therapeutic target for T-cell based immunotherapy or antibody therapy in a large panel of cancers. (C) 2012 Elsevier Inc. All rights reserved.

Six-transmembrane epithelial antigen of the prostate 3 (Steap3) is the major ferric reductase in developing erythrocytes. Steap family proteins are defined by a shared transmembrane domain that in Steap3 has been shown to function as a transmembrane electron shuttle, moving cytoplasmic electrons derived from NADPH across the lipid bilayer to the extracellular face where they are used to reduce Fe3+ to Fe2+ and potentially Cu2+ to Cu1+. Although the cytoplasmic N-terminal oxidoreductase domain of Steap3 and Steap4 are relatively well characterized, little work has been done to characterize the transmembrane domain of any member of the Steap family. Here we identify high affinity FAD and iron biding sites and characterize a single b-type heme binding site in the Steap3 transmembrane domain. Furthermore, we show that Steap3 is functional as a homodimer and that it utilizes an intrasubunit electron transfer pathway through the single heme moiety rather than an intersubunit electron pathway through a potential domain-swapped dimer. Importantly, the sequence motifs in the transmembrane domain that are associated with the FAD and metal binding sites are not only present in Steap2 and Steap4 but also in Steap1, which lacks the N-terminal oxidoreductase domain. This strongly suggests that Steap1 harbors latent oxidoreductase activity.