title: Nuclear-targeted deleted in liver cancer 1 (DLC1) is less efficient in exerting its tumor suppressive activity both in vitro and in vivo.
abstract: BACKGROUND
  Deleted in liver cancer 1 (DLC1) serves as an important RhoGTPase activating protein (RhoGAP) protein that terminates active RhoA signaling in human cancers. Increasing evidence has demonstrated that the tumor suppressive activity of DLC1 depends not only on RhoGAP activity, but also relies on proper focal adhesion localization through its interaction with tensin family proteins. Recently, there are reports showing that DLC1 can also be found in the nucleus; however, the existence and the relative tumor suppressive activity of nuclear DLC1 have never been clearly addressed.
  
  
  RESULTS
  We herein provide new evidence that DLC1 protein, which predominantly associated with focal adhesions and localized in cytosol, dynamically shuttled between cytoplasm and nucleus. Treatment of cells with nuclear export blocker, Leptomycin B (LMB), retained DLC1 in the nucleus. To understand the nuclear entry of DLC1, we identified amino acids 600-700 of DLC1 as a novel region that is important for its nuclear localization. The tumor suppressive activity of nuclear DLC1 was directly assessed by employing a nuclear localization signal (NLS) fusion variant of DLC1 (NLS-DLC1) with preferential nuclear localization. In SMMC-7721 HCC cells, expression of NLS-DLC1 failed to suppress colony formation and actin stress fiber formation in vitro. The abrogated tumor suppressive activity of nuclear DLC1 was demonstrated for the first time in vivo by subcutaneously injecting p53(-/-) RasV12 hepatoblasts with stable NLS-DLC1 expression in nude mice. The injected hepatoblasts with NLS-DLC1 expression effectively formed tumors when compared with the non-nuclear targeted DLC1.
  
  
  CONCLUSIONS
  Our study identified a novel region responsible for the nuclear entry of DLC1 and demonstrated the functional difference of DLC1 in different cellular compartments both in vitro and in vivo.
authors.affiliation: Department of Pathology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong.
authors.forename: Lo-Kong
authors.initials: LK
authors.lastname: Chan
authors.forename: Frankie Chi Fat
authors.initials: FC
authors.lastname: Ko
authors.forename: Karen Man-Fong
authors.initials: KM
authors.lastname: Sze
authors.forename: Irene Oi-Lin
authors.initials: IO
authors.lastname: Ng
authors.forename: Judy Wai Ping
authors.initials: JW
authors.lastname: Yam
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005434:Flow Cytometry; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D007150:Immunohistochemistry; D008113:Liver Neoplasms / Q000378:metabolism / Q000628:therapy; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008856:Microscopy, Fluorescence; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C112352:DLC1 protein, human; D005231:Fatty Acids, Unsaturated; D020690:GTPase-Activating Proteins; D025521:Tumor Suppressor Proteins; C038753:leptomycin B