Specific polypeptide differences in normal versus malignant breast tissue by two‐dimensional electrophoresis

Abstract

High resolution two‐dimensional polyacrylamide gel electrophoresis (2D‐PAGE) in combination with computer‐assisted densitometry was used to analyze 800–1000 silver stained postmitochrondrial and 600–800 cytosolic polypeptides extracted from malignant and nonmalignant human breast tissues. The 2D‐PAGE patterns of polypeptides from malignant and normal tissues were similar, although both qualitative and quantitative polypeptide differences were noted. Six cytosolic poly peptides (pI/ molecular mass X 10⁻³), 5.20/80, 5.75/43, 6.20/40, 5.43/35, 5.46/34.5, and 5.50/34 were detected exclusively in malignant tissues. One constitutive poly peptide, p52 (7.25/52), was not detected in tumor samples. Marked quantitative differences in spot density were noted in polypeptides localized mainly in the molecular weight ranges of 22–40 kDa and pI of 5.65–7.00. An overall increase in polypeptide expression was noted in this region of 2D‐PAGE gels of malignant tissues as compared to normal. Twenty‐two acidic and 19 polypeptides separated under nonequilibrium isoelectric focusing conditions were significantly increased in tumor samples while one polypeptide was decreased. One polypeptide, p24 (6.15/24), was expressed in greatest concentrations in tumors which also expressed the greatest estrogen receptor content. Expression of p24 was markedly reduced in normal tissue and in malignant tissues expressing low levels of estrogen and progesterone receptors. No significant differences in the expression of the Yb and Ya subunits of glutathione S‐transferases (GST)‐A, ‐B and ligandin were observed between normal and malignant breast tissue. None of the Yp subunits of the placental isoform of GST were detected in either normal or malignant breast tissues.