title: Expression cloning identifies transgelin (SM22) as a novel repressor of 92-kDa type IV collagenase (MMP-9) expression.
abstract: The 92-kDa gelatinase (MMP-9) expression is prerequisite for tissue remodeling in physiology and cancer. However, there are few known regulators of MMP-9 expression. Using an expression cloning strategy, we identified transgelin (SM22), a 22-25-kDa actin-binding protein localized to the cell membrane and cytoplasm, as a novel regulator of MMP-9 expression. Overexpression of a SM22 cDNA in HT1080 cells decreased MMP-9 mRNA/protein levels and diminished in vitro invasion of the latter rescued with exogenous MMP-9. Conversely, small interfering RNA-mediated knockdown of SM22 elevated MMP-9 synthesis, and uterus from SM22-null mice showed strong MMP-9 immunoreactivity compared with wild type animals. The ability of SM22 to repress MMP-9 expression required an intact amino terminus calponin homology domain. MMP-9 expression is driven by ERK signaling and SM22 targeted this pathway as evidenced by (a) the transience in MAPK activation and (b) blunted stimulation of the MMP-9 promoter by a constitutively active MEK expression vector. Progressive deletion analysis located the SM22 responsive region of the MMP-9 promoter to the proximal 90-bp region harboring an AP-1 motif subsequently implicated by site-directed mutagenesis. Furthermore, nuclear extract from the SM22 transfectants showed diminished c-Fos binding to this motif and SM22 expression reduced the activity of an AP-1-driven reporter by 75%. Thus, SM22 adds to a short list of repressors of MMP-9 expression, achieving this by reducing AP-1-dependent trans-activation of the gene by way of compromised ERK activation. Diminished transgelin expression in several cancers may thus partly account for the elevated MMP-9 expression evident in these tumors.
authors.affiliation: Department of Cancer Biology, M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Rajesh R
authors.initials: RR
authors.lastname: Nair
authors.forename: Julian
authors.initials: J
authors.lastname: Solway
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Boyd
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008168:Lung / Q000166:cytology; D020935:MAP Kinase Signaling System / Q000502:physiology; D020780:Matrix Metalloproteinase 9 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014599:Uterus / Q000166:cytology / Q000378:metabolism
chemical_list: D000199:Actins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D034741:RNA, Small Interfering; C051615:transgelin; D048049:Extracellular Signal-Regulated MAP Kinases; D020780:Matrix Metalloproteinase 9