title: SARPs: a family of secreted apoptosis-related proteins.
abstract: Quiescent mouse embryonic C3H/10T1/2 cells are more resistant to different proapoptotic stimuli than are these cells in the exponential phase of growth. However, the exponentially growing 10T1/2 cells are resistant to inhibitors of RNA or protein synthesis, whereas quiescent cells die upon these treatments. Conditioned medium from quiescent 10T1/2 cells possesses anti-apoptotic activity, suggesting the presence of protein(s) that function as an inhibitor of the apoptotic program. Using differential display technique, we identified and cloned a cDNA designated sarp1 (secreted apoptosis-related protein) that is expressed in quiescent but not in exponentially growing 10T1/2 cells. Hybridization studies with sarp1 revealed two additional family members. Cloning and sequencing of sarp2 and sarp3 revealed 38% and 40% sequence identity to sarp1, respectively. Human breast adenocarcinoma MCF7 cells stably transfected with sarp1 or infected with SARP1-expressing adenovirus became more resistant, whereas cells transfected with sarp2 displayed increased sensitivity to different proapoptotic stimuli. Expression of sarp family members is tissue specific. sarp mRNAs encode secreted proteins that possess a cysteine-rich domain (CRD) homologous to the CRD of frizzled proteins but lack putative membrane-spanning segments. Expression of SARPs modifies the intracellular levels of beta-catenin, suggesting that SARPs interfere with the Wnt-frizzled proteins signaling pathway.
authors.affiliation: LXR Biotechnology, Inc., 1401 Marina Way South, Richmond, CA 94804, USA. hmelkonyan@lxr.com
authors.forename: H S
authors.initials: HS
authors.lastname: Melkonyan
authors.forename: W C
authors.initials: WC
authors.lastname: Chang
authors.forename: J P
authors.initials: JP
authors.lastname: Shapiro
authors.forename: M
authors.initials: M
authors.lastname: Mahadevappa
authors.forename: P A
authors.initials: PA
authors.lastname: Fitzpatrick
authors.forename: M C
authors.initials: MC
authors.lastname: Kiefer
authors.forename: L D
authors.initials: LD
authors.lastname: Tomei
authors.forename: S R
authors.initials: SR
authors.lastname: Umansky
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D003001:Cloning, Molecular; D017077:Culture Media, Conditioned; D003598:Cytoskeletal Proteins / Q000378:metabolism; D051157:Frizzled Receptors; D015870:Gene Expression; D006801:Humans; D007399:Interphase / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D043562:Receptors, G-Protein-Coupled; D017981:Receptors, Neurotransmitter / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014018:Tissue Distribution; D015534:Trans-Activators; D014162:Transfection; D051176:beta Catenin
chemical_list: C495270:CTNNB1 protein, human; C495267:CTNNB1 protein, mouse; D017077:Culture Media, Conditioned; D003598:Cytoskeletal Proteins; C489742:FZD2 protein, human; D051157:Frizzled Receptors; C489743:Fzd2 protein, mouse; D043562:Receptors, G-Protein-Coupled; D017981:Receptors, Neurotransmitter; D015534:Trans-Activators; D051176:beta Catenin