title: Involvement of small ArfGAP1 (SMAP1), a novel Arf6-specific GTPase-activating protein, in microsatellite instability oncogenesis.
abstract: Small ArfGAP1 (stromal membrane-associated protein 1, SMAP1), a GTPase-activating protein specific for ADP-ribosylation factor 6 (Arf6), which is a small GTPase acting on membrane trafficking and actin remodeling, is frequently mutated in various tumors displaying microsatellite instability (MSI), notably in MSI colorectal cancers (CRC). Genotyping of 93 MSI CRCs (40 stage II, 32 stage III and 21 stage IV) allowed us to underscore that SMAP1 mutation frequency was inversely correlated with disease stage (P=0.01). Analysis of 46 cancer cell lines showed that SMAP1 mutations occurred only in MSI tumors, and consisted exclusively in short insertion or deletion in the coding 10-adenine repeat, generating a premature termination codon located downstream the ArfGAP domain. SMAP1 transcript levels were significant decreased (P=0.006), and truncated SMAP1 protein could not be detected in cells displaying biallelic SMAP1 mutations, owing to its sensitivity to proteasome degradation. To investigate the role of SMAP1 mutations, we used the SMAP1-null HCT116 cell line and we established three isogenic SMAP1-complemented clones. Cell proliferation was first assessed in vivo using subcutaneous xenografts into immunodeficient mice. Tumors developed in all animals regardless of the cell line injected, but tumor volumes were significantly smaller for both SMAP1-complemented clones compared with HCT116 (P<0.0001, at the time of killing). In vitro, SMAP1 mutations also increased cell clonogenicity (P=0.02-0.04), cell proliferation (P=0.008) by shortening the G2/M phase and decreased cell invasiveness (P=0.03-0.003). In keeping, SMAP1-complemented HCT116 gained several mesenchymal markers (Snail, Slug and vimentin) considered as a hallmark of epithelial-to-mesenchymal transition. These observations are reminiscent of some clinical characteristics of MSI CRCs, notably their larger size and lower rate of metastasis. Our observations suggest that SMAP1 loss-of-function mutations in MSI CRC may contribute to the emerging oncogenic pathway involving abnormal Arf6 regulation.
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: F
authors.initials: F
authors.lastname: Sangar
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: A-S
authors.initials: AS
authors.lastname: Schreurs
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: C
authors.initials: C
authors.lastname: Umaña-Diaz
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: A
authors.initials: A
authors.lastname: Clapéron
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: C
authors.initials: C
authors.lastname: Desbois-Mouthon
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: C
authors.initials: C
authors.lastname: Calmel
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: O
authors.initials: O
authors.lastname: Mauger
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: A
authors.initials: A
authors.lastname: Zaanan
authors.affiliation: Department of Pathology, Sainte-Anne Hospital, University Paris Descartes, Paris, France.
authors.forename: C
authors.initials: C
authors.lastname: Miquel
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France [3] Department of Pathology, Saint-Antoine Hospital, AP-HP, Paris, France.
authors.forename: J-F
authors.initials: JF
authors.lastname: Fléjou
authors.affiliation: 1] INSERM, UMR_S 938, Saint-Antoine Research Center, Paris, France [2] UPMC Univ Paris 06, UMR_S 938, Saint-Antoine Research Center, Paris, France.
authors.forename: F
authors.identifier: 0000000253538889
authors.initials: F
authors.lastname: Praz
mesh_terms: D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000378:metabolism*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D063646:Carcinogenesis / Q000378:metabolism*; D002465:Cell Movement; D049109:Cell Proliferation; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D004252:DNA Mutational Analysis; D005260:Female; D020690:GTPase-Activating Proteins / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D045325:HCT116 Cells; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D053842:Microsatellite Instability; D008875:Middle Aged; D009154:Mutation; D009368:Neoplasm Transplantation; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D047368:Tumor Burden; D014746:Vimentin / Q000235:genetics / Q000378:metabolism
chemical_list: D000089982:ADP-Ribosylation Factor 6; D020690:GTPase-Activating Proteins; D008565:Membrane Proteins; C107022:SMAP1 protein, human; C553893:SMAP2 protein, human; C000604407:SNAI1 protein, human; C000604449:Snai2 protein, mouse; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors; D014746:Vimentin; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; C000715727:Arf6 protein, mouse