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Phosphorylation of pRb: mechanism for RB pathway inactivation in MYCN-amplified retinoblastoma

Kathryn G Ewens1, Tricia R Bhatti2,3, Kimberly A Moran1

  • 1Department of Genetics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.

Cancer Medicine
|February 18, 2017
PubMed

Insights

High MYCN amplification can drive retinoblastoma (RB1) tumor growth even without RB1 gene mutations. In these cases, the pRb protein is inactivated by phosphorylation, highlighting RB1 inactivation as crucial for tumor initiation.

Area of Science:

  • Oncology
  • Molecular Biology
  • Genetics

Background:

  • Retinoblastoma (RB1) is a pediatric eye cancer.
  • RB1 gene mutations are common in retinoblastoma.
  • A unique subgroup lacks RB1 mutations but shows MYCN amplification.

Purpose of the Study:

  • Investigate alternative pRb inactivation pathways in retinoblastoma.
  • Determine the role of MYCN amplification in RB1 tumors.
  • Clarify RB1 inactivation mechanisms in retinoblastoma tumorigenesis.

Main Methods:

  • Analyzed RB1 mutation status and MYCN copy number in 245 retinoblastomas.
  • Assessed pRb and phosphorylated pRb (ppRb) levels via immunohistochemistry in five tumors.
  • Correlated MYCN amplification with RB1 mutation status and pRb phosphorylation.

Main Results:

  • 13% of tumors had no detectable RB1 mutations (RB1+/+).
  • Six RB1+/+ tumors exhibited high MYCN amplification (29-110 copies).
  • RB1+/+ and RB1+/- tumors with MYCN amplification showed high pRb and ppRb levels, unlike RB1-/- tumors.

Conclusions:

  • High MYCN amplification occurs in retinoblastoma with or without RB1 mutations.
  • Phosphorylation inactivates pRb in MYCN-amplified retinoblastoma lacking RB1 mutations.
  • RB1 inactivation (mutation or phosphorylation) is essential for retinoblastoma initiation, irrespective of MYCN amplification.
Keywords:
Childhood-onset ocular tumorMYCN amplificationRB1 mutation-negative retinoblastomapRb and ppRb expression in RBpRb inactivation by phosphorylation

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