title: Transforming growth factor-beta (TGF-beta)-inducible gene TMEPAI converts TGF-beta from a tumor suppressor to a tumor promoter in breast cancer.
abstract: TMEPAI is a transforming growth factor-beta (TGF-beta)-induced transmembrane protein that is overexpressed in several cancers. How TMEPAI expression relates to malignancy is unknown. Here, we report high expression of TMEPAI in estrogen receptor/progesterone receptor-negative and human epidermal growth factor receptor-2-negative breast cancer cell lines and primary breast cancers that was further increased by TGF-beta treatment. Basal and TGF-beta-induced expression of TMEPAI were inhibited by the TGF-beta receptor antagonist SB431542 and overexpression of Smad7 or a dominant-negative mutant of Alk-5. TMEPAI knockdown attenuated TGF-beta-induced growth and motility in breast cancer cells, suggesting a role for TMEPAI in growth promotion and invasiveness. Further, TMEPAI knockdown decreased breast tumor mass in a mouse xenograft model in a manner associated with increased expression of phosphatase and tensin homologue (PTEN) and diminished phosphorylation of Akt. Consistent with the effects through the phosphatidylinositol 3-kinase pathway, tumors with TMEPAI knockdown exhibited elevated levels of the cell cycle inhibitor p27kip1 and attenuated levels of DNA replication and expression of hypoxia-inducible fator 1alpha and vascular endothelial growth factor. Together, these results suggest that TMEPAI functions in breast cancer as a molecular switch that converts TGF-beta from a tumor suppressor to a tumor promoter.
authors.affiliation: Department of Pathology, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229, USA.
authors.forename: Prajjal K
authors.initials: PK
authors.lastname: Singha
authors.forename: I-Tien
authors.initials: IT
authors.lastname: Yeh
authors.forename: Manjeri A
authors.initials: MA
authors.lastname: Venkatachalam
authors.forename: Pothana
authors.initials: P
authors.lastname: Saikumar
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D018270:Carcinoma, Ductal, Breast / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D048708:Cell Growth Processes / Q000235:genetics; D002465:Cell Movement / Q000235:genetics; D005260:Female; D005784:Gene Amplification; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D008819:Mice, Nude; D034741:RNA, Small Interfering / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D008565:Membrane Proteins; C412868:PMEPA1 protein, human; D034741:RNA, Small Interfering; D016212:Transforming Growth Factor beta