title: GM3 suppresses anchorage-independent growth via Rho GDP dissociation inhibitor beta in melanoma B16 cells.
abstract: Ly-GDI, Rho GTPase dissociation inhibitor beta, was found to be expressed parallel to the GM3 level in mouse B16 cells whose GM3 contents were modified by B4galt6 sense, B4galt6 antisense cDNA, or St3galt5 siRNA transfection. Ly-GDI expression was increased on GM3 addition to these cells and decreased with D-PDMP treatment, a glucosylceramide synthesis inhibitor. Suppression of GM3 or Ly-GDI by RNAi was concomitantly associated with an increase in anchorage-independent growth in soft agar. These results clearly indicate that GM3 suppresses anchorage-independent growth through Ly-GDI. GM3 signals regulating Ly-GDI expression was inhibited by LY294002, siRNA against Akt1 and Akt2 and rapamycin, showing that GM3 signals are transduced via the PI3K/Akt/mTOR pathway. Either siRNA towards Rictor or Raptor suppressed Ly-GDI expression. The Raptor siRNA suppressed the effects of GM3 on Ly-GDI expression and Akt phosphorylation at Thr(308) , suggesting GM3 signals to be transduced to mTOR-Raptor and Akt-Thr(308) , leading to Ly-GDI stimulation. siRNA targeting Pdpk1 reduced Akt phosphorylation at Thr(308) and rendered the cells insensitive to GM3 stimulation, indicating that Akt-Thr(308) plays a critical role in the pathway. The components aligned in this pathway showed similar effects on anchorage-independent growth as GM3 and Ly-GDI. Taken together, GM3 signals are transduced in B16 cells through PI3K, Pdpk1, Akt(Thr308) and the mTOR/Raptor pathway, leading to enhanced expression of Ly-GDI mRNA, which in turn suppresses anchorage-independent growth in melanoma B16 cells.
authors.affiliation: Laboratory of Tumor Biology and Glycobiology, Department of Life Sciences, Shenyang Pharmaceutical University, Shenyang, China.
authors.forename: Pu
authors.initials: P
authors.lastname: Wang
authors.forename: Su
authors.initials: S
authors.lastname: Xu
authors.forename: Yinan
authors.initials: Y
authors.lastname: Wang
authors.forename: Peixing
authors.initials: P
authors.lastname: Wu
authors.forename: Jinghai
authors.initials: J
authors.lastname: Zhang
authors.forename: Toshinori
authors.initials: T
authors.lastname: Sato
authors.forename: Sadako
authors.initials: S
authors.lastname: Yamagata
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Yamagata
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005679:G(M3) Ganglioside / Q000502:physiology*; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000235:genetics / Q000502:physiology*; D008546:Melanoma, Experimental / Q000473:pathology*; D051379:Mice; D015778:Minor Histocompatibility Antigens; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000502:physiology; D062949:rho Guanine Nucleotide Dissociation Inhibitor beta; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
chemical_list: D064413:3-Phosphoinositide-Dependent Protein Kinases; D005679:G(M3) Ganglioside; D020730:Guanine Nucleotide Dissociation Inhibitors; D015778:Minor Histocompatibility Antigens; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D062949:rho Guanine Nucleotide Dissociation Inhibitor beta; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; C569659:Arhgdib protein, mouse; C546843:mTOR protein, mouse; C578564:Pdpk1 protein, mouse