title: FOXP3 is a novel transcriptional repressor for the breast cancer oncogene SKP2.
abstract: S-phase kinase-associated protein 2 (SKP2) is a component of the E3 ubiquitin ligase SKP1-Cul1-Fbox complex. Overexpression of SKP2 results in cell cycle dysregulation and carcinogenesis; however, the genetic lesions that cause this upregulation are poorly understood. We recently demonstrated that forkhead box P3 (FOXP3) is an X-linked breast cancer suppressor and an important repressor of the oncogene ERBB2/HER2. Since FOXP3 suppresses tumor growth regardless of whether the tumors overexpress ERBB2/HER2, additional FOXP3 targets may be involved in its tumor suppressor activity. Here, we show that mammary carcinomas from mice heterozygous for a Foxp3 mutation exhibited increased Skp2 expression. Ectopic expression of FOXP3 in mouse mammary cancer cells repressed SKP2 expression with a corresponding increase in p27 and polyploidy. Conversely, siRNA silencing of the FOXP3 gene in human mammary epithelial cells increased SKP2 expression. We also show that Foxp3 directly interacted with and repressed the Skp2 promoter. Moreover, the analysis of over 200 primary breast cancer samples revealed an inverse correlation between FOXP3 and SKP2 levels. Finally, we demonstrated that downregulation of SKP2 was critical for FOXP3-mediated growth inhibition in breast cancer cells that do not overexpress ERBB2/HER2. Our data provide genetic, biochemical, and functional evidence that FOXP3 is a novel transcriptional repressor for the oncogene SKP2.
authors.affiliation: Department of Surgery, Section of General Surgery, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Tao
authors.initials: T
authors.lastname: Zuo
authors.forename: Runhua
authors.initials: R
authors.lastname: Liu
authors.forename: Huiming
authors.initials: H
authors.lastname: Zhang
authors.forename: Xing
authors.initials: X
authors.lastname: Chang
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Lizhong
authors.initials: L
authors.lastname: Wang
authors.forename: Pan
authors.initials: P
authors.lastname: Zheng
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D044842:Cullin Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D051858:Forkhead Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D020868:Gene Silencing; D050172:Genes, X-Linked; D006579:Heterozygote; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008817:Mice, Mutant Strains; D015513:Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D011003:Ploidies; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D044786:S-Phase Kinase-Associated Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D044842:Cullin Proteins; D051858:Forkhead Transcription Factors; D015513:Oncogene Proteins; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D012097:Repressor Proteins; D044786:S-Phase Kinase-Associated Proteins; D025521:Tumor Suppressor Proteins; C100318:Cullin 1; C418974:FOXP3 protein, human; C498833:Foxp3 protein, mouse; C524056:Erbb2 protein, mouse