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Cdc42 and Ras cooperate to mediate cellular transformation by intersectin-L

Jian-Bin Wang1, Wen Jin Wu, Richard A Cerione

  • 1Department of Molecular Medicine, Veterinary Medical Center, Cornell University, Ithaca, New York 14853, USA.

The Journal of Biological Chemistry
|April 13, 2005
PubMed

Insights

The study reveals that a specific intersectin-L protein fragment (SH3A-C2) transforms cells by cooperating with Ras, not by altering epidermal growth factor receptor (EGFR) signaling. This finding clarifies mechanisms of cellular transformation involving Cdc42.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Oncology

Background:

  • Cdc42 (a Ras-related GTP-binding protein) regulates key cellular processes including actin cytoskeleton organization, membrane trafficking, cell-cycle progression, and malignant transformation.
  • Previous work demonstrated that a fast-cycling Cdc42 mutant (Cdc42(F28L)) transforms NIH 3T3 cells by disrupting epidermal growth factor receptor (EGFR)-Cbl interactions and subsequent EGFR down-regulation.

Purpose of the Study:

  • To investigate the relationship between Cdc42 hyperactivation and its impact on EGFR signaling, leading to cellular transformation.
  • To elucidate the role of different intersectin-L protein domains in modulating Cdc42 activity and cellular transformation.

Main Methods:

  • Expression of various intersectin-L protein fragments in fibroblasts.
  • Assessing guanine nucleotide exchange factor (GEF) activity of intersectin-L fragments on Cdc42.
  • Evaluating cellular transformation phenotypes, including growth in low serum and colony formation in soft agar.
  • Analyzing effects on EGFR levels and epidermal growth factor (EGF)-coupled signaling through ERK.

Main Results:

  • A truncated intersectin-L fragment (SH3A-C2) containing DH, PH, and C2 domains exhibited significant GEF activity, strongly activating Cdc42.
  • SH3A-C2 potently stimulated cell growth in low serum and colony formation in soft agar, indicating potent transforming activity.
  • Unlike the Cdc42(F28L) mutant, SH3A-C2 did not significantly alter EGFR levels or the duration of EGF-induced ERK signaling.
  • SH3A-C2 mediated cellular transformation primarily through cooperation between Ras and Cdc42, rather than through EGFR pathway modulation.

Conclusions:

  • The intersectin-L SH3A-C2 fragment transforms fibroblasts through a mechanism involving Ras-Cdc42 cooperation.
  • This pathway of cellular transformation is distinct from the EGFR-dependent mechanism observed with the fast-cycling Cdc42(F28L) mutant.
  • These findings highlight the diverse roles of intersectin-L in regulating cell signaling and transformation.

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