Loss of giant obscurins from breast epithelium promotes epithelial-to-mesenchymal transition, tumorigenicity and metastasis

Oncogene. 2015 Aug 6;34(32):4248-59. doi: 10.1038/onc.2014.358. Epub 2014 Nov 10.

Abstract

Obscurins, encoded by the single OBSCN gene, are giant cytoskeletal proteins with structural and regulatory roles. The OBSCN gene is highly mutated in different types of cancers. Loss of giant obscurins from breast epithelial cells confers them with a survival and growth advantage, following exposure to DNA-damaging agents. Here we demonstrate that the expression levels and subcellular distribution of giant obscurins are altered in human breast cancer biopsies compared with matched normal samples. Stable clones of non-tumorigenic MCF10A cells lacking giant obscurins fail to form adhesion junctions, undergo epithelial-to-mesenchymal transition and generate >100-μm mammospheres bearing markers of cancer-initiating cells. Obscurin-knockdown MCF10A cells display markedly increased motility as a sheet in 2-dimensional (2D) substrata and individually in confined spaces and invasion in 3D matrices. In line with these observations, actin filaments redistribute to extending filopodia where they exhibit increased dynamics. MCF10A cells that stably express the K-Ras oncogene and obscurin short hairpin RNA (shRNA), but not scramble control shRNA, exhibit increased primary tumor formation and lung colonization after subcutaneous and tail vein injections, respectively. Collectively, our findings reveal that loss of giant obscurins from breast epithelium results in disruption of the cell-cell contacts and acquisition of a mesenchymal phenotype that leads to enhanced tumorigenesis, migration and invasiveness in vitro and in vivo.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Biopsy
  • Blotting, Western
  • Breast / metabolism*
  • Breast / pathology
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Cadherins / genetics
  • Cadherins / metabolism
  • Cell Adhesion / genetics
  • Cell Line
  • Cell Movement / genetics
  • Cell Transformation, Neoplastic / genetics*
  • Cell Transformation, Neoplastic / metabolism
  • Epithelial Cells / metabolism
  • Epithelial-Mesenchymal Transition / genetics*
  • Epithelium / metabolism
  • Female
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Intercellular Junctions / metabolism
  • Microscopy, Confocal
  • Neoplasm Metastasis
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins p21(ras)
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Rho Guanine Nucleotide Exchange Factors / genetics*
  • Rho Guanine Nucleotide Exchange Factors / metabolism
  • Transplantation, Heterologous
  • Vimentin / genetics
  • Vimentin / metabolism
  • ras Proteins / genetics
  • ras Proteins / metabolism

Substances

  • Cadherins
  • KRAS protein, human
  • Proto-Oncogene Proteins
  • RNA, Small Interfering
  • Rho Guanine Nucleotide Exchange Factors
  • Vimentin
  • OBSCN protein, human
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins p21(ras)
  • ras Proteins