title: Tumor Suppressor Activity of Klotho in Breast Cancer Is Revealed by Structure-Function Analysis.
abstract: Klotho is a transmembrane protein containing two internal repeats, KL1 and KL2, both displaying significant homology to members of the β-glycosidase family. Klotho is expressed in the kidney, brain, and various endocrine tissues, but can also be cleaved and act as a circulating hormone. Klotho is an essential cofactor for binding of fibroblast growth factor 23 (FGF23) to the FGF receptor and can also inhibit the insulin-like growth factor-1 (IGF-1) pathway. Data from a wide array of malignancies indicate klotho as a tumor suppressor; however, the structure-function relationships governing its tumor suppressor activities have not been deciphered. Here, the tumor suppressor activities of the KL1 and KL2 domains were examined. Overexpression of either klotho or KL1, but not of KL2, inhibited colony formation by MCF-7 and MDA-MB-231 cells. Moreover, in vivo administration of KL1 was not only well tolerated but significantly slowed tumor formation in nude mice. Further studies indicated that KL1, but not KL2, interacted with the IGF-1R and inhibited the IGF-1 pathway. Based on computerized structural modeling, klotho constructs were generated in which critical amino acids have been mutated. Interestingly, the mutated proteins retained their tumor suppressor activity but showed reduced ability to modulate FGF23 signaling. These data indicate differential activity of the klotho domains, KL1 and KL2, in breast cancer and reveal that the tumor suppressor activities of klotho can be dissected from its physiologic activities.
  
  
  CONCLUSIONS
  These findings pave the way for a rational design of safe klotho-based molecules for the treatment of breast cancer.
authors.affiliation: The Oncology Division, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel. Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Hagai
authors.initials: H
authors.lastname: Ligumsky
authors.affiliation: The Oncology Division, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel.
authors.forename: Tami
authors.initials: T
authors.lastname: Rubinek
authors.affiliation: The Oncology Division, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel. Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Keren
authors.initials: K
authors.lastname: Merenbakh-Lamin
authors.affiliation: Bioinformatics Unit, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Adva
authors.initials: A
authors.lastname: Yeheskel
authors.affiliation: Bioinformatics and Biological Computing Unit, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Rotem
authors.initials: R
authors.lastname: Sertchook
authors.affiliation: The Oncology Division, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel. Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Shiri
authors.initials: S
authors.lastname: Shahmoon
authors.affiliation: Department of Pathology, Talpiot Medical Leadership Program, Chaim Sheba Medical Center, Ramat Gan, Israel.
authors.forename: Sarit
authors.initials: S
authors.lastname: Aviel-Ronen
authors.affiliation: The Oncology Division, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel. Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel. idow@tlvmc.gov.il.
authors.forename: Ido
authors.initials: I
authors.lastname: Wolf
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005966:Glucuronidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D064593:Heterografts; D006801:Humans; D000090265:Klotho Proteins; D061986:MCF-7 Cells; D008297:Male; D051379:Mice; D008819:Mice, Nude; D008958:Models, Molecular; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: C000717427:FGF23 protein, human; C000717428:Fgf23 protein, mouse; D000089703:Fibroblast Growth Factor-23; D005966:Glucuronidase; D000090265:Klotho Proteins