Depletion of Ras Suppressor-1 (RSU-1) promotes cell invasion of breast cancer cells through a compensatory upregulation of a truncated isoform

Sci Rep. 2019 Jul 11;9(1):10050. doi: 10.1038/s41598-019-46575-0.

Abstract

Extracellular matrix (ECM)-adhesion proteins and actin cytoskeleton are pivotal in cancer cell invasion. Ras Suppressor-1 (RSU-1), a cell-ECM adhesion protein that interacts with PINCH-1, thus being connected to Integrin Linked Kinase (ILK), alpha-parvin (PARVA), and actin cytoskeleton, is up-regulated in metastatic breast cancer (BC) samples. Apart from the originally-identified gene (RSU-1L), an alternatively-spliced isoform (RSU-1-X1) has been reported. We used non-invasive MCF-7 cells, expressing only RSU-1L, and highly invasive MDA-MB-231-LM2 expressing both isoforms and generated stable shRNA-transduced cells lacking RSU-1L, while the truncated RSU-1-X1 isoform was depleted by siRNA-mediated silencing. RSU-1L depletion in MCF-7 cells resulted in complete abrogation of tumor spheroid invasion in three-dimensional collagen gels, whereas it promoted MDA-MB-231-LM2 invasion, through a compensatory upregulation of RSU-1-X1. When RSU-1-X1 was also eliminated, RSU-1L-depletion-induced migration and invasion were drastically reduced being accompanied by reduced urokinase plasminogen activator expression. Protein expression analysis in 23 human BC samples corroborated our findings showing RSU-1L to be upregulated and RSU-1-X1 downregulated in metastatic samples. We demonstrate for the first time, that both RSU-1 isoforms promote invasion in vitro while RSU-1L elimination induces RSU-1-X1 upregulation to compensate for the loss. Hence, we propose that both isoforms should be blocked to effectively eliminate metastasis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / metabolism
  • Adaptor Proteins, Signal Transducing / metabolism
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Cell Movement
  • Extracellular Matrix / metabolism*
  • Humans
  • LIM Domain Proteins / metabolism
  • MCF-7 Cells
  • Membrane Proteins / metabolism
  • Molecular Targeted Therapy
  • Neoplasm Invasiveness
  • Neoplasm Metastasis
  • Protein Isoforms / genetics
  • RNA, Small Interfering / genetics
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Up-Regulation
  • Urokinase-Type Plasminogen Activator / genetics
  • Urokinase-Type Plasminogen Activator / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • LIM Domain Proteins
  • LIMS1 protein, human
  • Membrane Proteins
  • Protein Isoforms
  • RNA, Small Interfering
  • Transcription Factors
  • RSU1 protein, human
  • Urokinase-Type Plasminogen Activator