title: Tumor promoting effect of podoplanin-positive fibroblasts is mediated by enhanced RhoA activity.
abstract: There is growing evidence that stromal fibroblasts can promote tumor progression via several mechanisms. We previously reported that podoplanin (PDPN) expressed on stromal fibroblasts is functionally protein responsible for the promotion of tumor formation in mouse subcutaneous tissue. The purpose of the present study was to reveal the molecular mechanism by which PDPN on stromal fibroblasts promotes tumor formation. The subcutaneous co-injection of the human lung adenocarcinoma cell line A549 and human fibroblasts (hFbs) overexpressing wild-type podoplanin (WT-PDPN) promoted subcutaneous tumor formation, compared with the co-injection of A549 and control hFbs (64% vs 21%). On the other hand, hFbs expressing PDPN mutant in which the cytoplasmic domain of PDPN was deleted (PDPN-Del.IC), resulted in a relatively lower level of tumor formation (33%). Since PDPN reportedly regulates RhoA activity through its cytoplasmic domain, we measured the activation state of RhoA in hFbs expressing WT-PDPN. RhoA activity was 2.7-fold higher in WT-PDPN expressing hFbs than in control hFbs. Furthermore, the subcutaneous co-injection of hFbs expressing constitutive active RhoA (G14VRhoA) and A549 cells enhanced tumor formation compared with the co-injection of the same cell line and control hFbs. These results indicate that enhanced RhoA activity in hFbs expressing PDPN may be one of the mechanisms resulting in the promotion of tumor formation, suggesting that biomechanical remodeling of the microenvironment by stromal fibroblasts may play important roles in tumor progression.
authors.affiliation: Laboratory of Cancer Biology, Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Suguru
authors.initials: S
authors.lastname: Ito
authors.forename: Genichiro
authors.initials: G
authors.lastname: Ishii
authors.forename: Ayuko
authors.initials: A
authors.lastname: Hoshino
authors.forename: Hiroko
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Shinya
authors.initials: S
authors.lastname: Neri
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kuwata
authors.forename: Morihiro
authors.initials: M
authors.lastname: Higashi
authors.forename: Kanji
authors.initials: K
authors.lastname: Nagai
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ochiai
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009369:Neoplasms / Q000201:enzymology / Q000473:pathology*; D017434:Protein Structure, Tertiary / Q000235:genetics; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D000098853:Podoplanin
chemical_list: D008562:Membrane Glycoproteins; D020742:rhoA GTP-Binding Protein; C117468:PDPN protein, human; D000098853:Podoplanin; C066737:RHOA protein, human