Analysis of phosphorylation of pRB and its regulatory proteins in breast cancer

J Clin Pathol. 1997 May;50(5):407-12. doi: 10.1136/jcp.50.5.407.

Abstract

Aim: In order to study the role of retinoblastoma protein (pRB) in breast cancer, the phosphorylation of pRB and the expression of its related proteins-such as cyclin E, cyclin dependent kinase 2 (Cdk2), and p21/Cdk interacting protein 1 (Cip1)-were examined in 30 breast cancers in which pRB overexpression was confirmed immunohistochemically.

Methods: The phosphorylation of pRB for 30 tumours was investigated with western blotting. The expression of pRB, Cdk2/Cdc2, cyclin E, and p21/Cip1 was identified by immunohistochemistry and western blotting.

Results: The expression of pRB was confirmed in 52 of 70 tumours (74%) by immunostaining. Western blotting for pRB showed that 25 of 30 representative cancers (83%) were underphosphorylated, while only five tumours showed the hyperphosphorylated form of pRB. However, cyclin E and Cdk2-which promote phosphorylation of pRB-were expressed in all tumours. On the other hand p21/Cip1, a Cdk2 inhibitor, was expressed in 18 of 25 tumours with underphosphorylated pRB, while four of the five tumours with hyperphosphorylated pRB showed no expression of p21/Cip1. Examination of the relation between pRB phosphorylation and clinicopathological variables showed that the underphosphorylated group was characterised by low risk of lymph node metastasis (p < 0.01).

Conclusions: The phosphorylation of pRB appears to be regulated mainly by p21/Cip1 through the suppression of cyclin E and Cdk2 in breast cancer. The underphosphorylated form of pRB may be useful as a prognostic factor.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Biomarkers, Tumor / metabolism*
  • Blotting, Western
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • CDC2-CDC28 Kinases*
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclin-Dependent Kinases / metabolism
  • Cyclins / metabolism
  • Female
  • Humans
  • Lymphatic Metastasis
  • Middle Aged
  • Neoplasm Proteins / metabolism*
  • Phosphorylation
  • Protein Serine-Threonine Kinases / metabolism
  • Retinoblastoma Protein / metabolism*
  • Tumor Cells, Cultured

Substances

  • Biomarkers, Tumor
  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Neoplasm Proteins
  • Retinoblastoma Protein
  • Protein Serine-Threonine Kinases
  • CDC2-CDC28 Kinases
  • CDK2 protein, human
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases