Tetraspanin 8 is a novel regulator of ILK-driven β1 integrin adhesion and signaling in invasive melanoma cells

Oncotarget. 2017 Mar 7;8(10):17140-17155. doi: 10.18632/oncotarget.15084.

Abstract

Melanoma is well known for its propensity for lethal metastasis and resistance to most current therapies. Tumor progression and drug resistance depend to a large extent on the interplay between tumor cells and the surrounding matrix. We previously identified Tetraspanin 8 (Tspan8) as a critical mediator of melanoma invasion, whose expression is absent in healthy skin. The present study investigated whether Tspan8 may influence cell-matrix anchorage and regulate downstream molecular pathways leading to an aggressive behavior. Using silencing and ectopic expression strategies, we showed that Tspan8-mediated invasion of melanoma cells resulted from defects in cell-matrix anchorage by interacting with β1 integrins and by interfering with their clustering, without affecting their surface or global expression levels. These effects were associated with impaired phosphorylation of integrin-linked kinase (ILK) and its downstream target Akt-S473, but not FAK. Specific blockade of Akt or ILK activity strongly affected cell-matrix adhesion. Moreover, expression of a dominant-negative form of ILK reduced β1 integrin clustering and cell-matrix adhesion. Finally, we observed a tumor-promoting effect of Tspan8 in vivo and a mutually exclusive expression pattern between Tspan8 and phosphorylated ILK in melanoma xenografts and human melanocytic lesions. Altogether, the in vitro, in vivo and in situ data highlight a novel regulatory role for Tspan8 in melanoma progression by modulating cell-matrix interactions through β1 integrin-ILK axis and establish Tspan8 as a negative regulator of ILK activity. These findings emphasize the importance of targeting Tspan8 as a means of switching from low- to firm-adhesive states, mandatory to prevent tumor dissemination.

Keywords: ILK; integrin; matrix; melanoma; tetraspanin 8.

MeSH terms

  • Animals
  • Blotting, Western
  • Cell Adhesion / genetics
  • Cell Line, Tumor
  • Cell Movement / genetics
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Integrin beta1 / genetics*
  • Integrin beta1 / metabolism
  • Male
  • Melanoma / genetics*
  • Melanoma / metabolism
  • Melanoma / pathology
  • Mice, Nude
  • Microscopy, Confocal
  • Mutation
  • Neoplasm Invasiveness
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / genetics*
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism
  • RNA Interference
  • Signal Transduction / genetics*
  • Tetraspanins / genetics*
  • Tetraspanins / metabolism
  • Transplantation, Heterologous

Substances

  • Integrin beta1
  • TSPAN8 protein, human
  • Tetraspanins
  • integrin-linked kinase
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt