title: Hypoxic conversion of SMAD7 function from an inhibitor into a promoter of cell invasion.
abstract: Smad7 is an inhibitor of the transforming growth factor-beta-activated signaling pathway. Under well-oxygenated conditions, Smad7 is a potent inhibitor of carcinoma cell invasion. Paradoxically, however, the expression of Smad7 is upregulated across several cancers and may promote cancer progression. Hypoxia, which is frequently met in solid tumors, is an enhancer of carcinoma cell invasion and cancer progression. Here, we report that hypoxia activates the expression of Smad7 in a hypoxia-inducible factor- and von Hippel-Lindau protein-dependent manner. As expected, in normoxia, the forced expression of Smad7 inhibited carcinoma cell invasion. In contrast with the normoxic condition, the inhibitory effect of Smad7 was lost under hypoxia. The block in carcinoma cell invasion by forced expression of Smad7 was released by hypoxia in two invasive carcinoma cell lines. Moreover, the noninvasive HaCaT keratinocytes become invasive upon simultaneous hypoxia and transforming growth factor-beta stimulus. The hypoxia-activated invasion was attenuated by inhibiting Smad7 expression by short interfering RNA. Finally, the increased Smad7 expression in human carcinomas correlated with hypoxic gene expression. The data provide evidence that hypoxia could convert Smad7 function from an invasion inhibitor into an activator of invasion. Furthermore, they might shed light as to why increased Smad7 expression is detected in cancers.
authors.affiliation: Department of Otorhinolaryngology, Turku Centre for Biotechnology, Turku University and Abo Akademi University, School of Biological Sciences and Medicity Research Laboratories, Turku University Hospital, Turku, Finland.
authors.forename: Pekka T
authors.initials: PT
authors.lastname: Heikkinen
authors.forename: Marika
authors.initials: M
authors.lastname: Nummela
authors.forename: Terhi
authors.initials: T
authors.lastname: Jokilehto
authors.forename: Reidar
authors.initials: R
authors.lastname: Grenman
authors.forename: Veli-Matti
authors.initials: VM
authors.lastname: Kähäri
authors.forename: Panu M
authors.initials: PM
authors.lastname: Jaakkola
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000378:metabolism* / Q000473:pathology*; D015687:Cell Hypoxia / Q000502:physiology; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D006258:Head and Neck Neoplasms / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism; D015603:Keratinocytes / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D010766:Phosphorylation; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051896:Smad Proteins, Receptor-Regulated / Q000037:antagonists & inhibitors / Q000378:metabolism; D051906:Smad7 Protein / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; D051896:Smad Proteins, Receptor-Regulated; D051906:Smad7 Protein; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human; C497806:SMAD7 protein, human