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Inactivation of the Rb pathway and overexpression of both isoforms of E2F3 are obligate events in bladder tumours

C D Hurst1, D C Tomlinson, S V Williams

  • 1Cancer Research UK Clinical Centre, Leeds Institute of Molecular Medicine, St James's University Hospital, Leeds, UK.

Oncogene
|November 27, 2007
PubMed

Insights

Amplification of the 6p22 region in bladder cancer leads to overexpression of E2F3, inhibiting proliferation. Inactivation of the Retinoblastoma (Rb) pathway is also crucial for tumor development in these cases.

Area of Science:

  • Oncology
  • Molecular Biology
  • Genetics

Background:

  • The 6p22 chromosomal region contains candidate genes E2F3 and CDKAL1, frequently amplified in bladder cancer.
  • E2F3 isoforms (E2F3a and E2F3b) and CDKAL1 expression were investigated in bladder cancer cell lines with 6p22 amplification.

Purpose of the Study:

  • To examine the role of E2F3 and CDKAL1 in bladder cancer proliferation.
  • To investigate the relationship between 6p22 amplification, E2F3 overexpression, and Retinoblastoma (Rb) pathway inactivation in bladder tumors.

Main Methods:

  • shRNA-mediated knockdown of CDKAL1 and E2F3 isoforms in bladder cancer cell lines.
  • Analysis of Rb protein expression and phosphorylation status.
  • Array comparative genomic hybridization (Array-CGH) to detect 6p22.3 amplification in primary bladder tumors.

Main Results:

  • Overexpression of both E2F3 isoforms and CDKAL1 was observed in 6p22-amplified bladder cancer cell lines.
  • Knockdown of E2F3a or E2F3b, particularly together, significantly inhibited proliferation; CDKAL1 knockdown had no effect.
  • A strong correlation was found between 6p22.3 amplification, E2F3 overexpression, and loss of Rb expression in both cell lines and primary tumors.
  • Primary tumors with 6p22.3 amplification showed either loss of RB1 (leading to no Rb protein) or deletion of CDKN2A (leading to inactive Rb protein via p16 loss).

Conclusions:

  • E2F3 overexpression is a key driver of proliferation in a subset of bladder cancers with 6p22 amplification.
  • Inactivation of the Rb pathway, through RB1 loss or CDKN2A deletion, is a necessary co-event for tumor development in these cases.
  • Targeting E2F3 and the Rb pathway presents potential therapeutic strategies for bladder cancer.

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