Intranuclear Nucleolin Distribution during Cell Cycle Progression in Human Invasive Ductal Breast Carcinomas in Relation to Estrogen Receptor Status

Abstract

Background: Nucleolin (NU) can be found in the nucleus in aggregates and in a diffused form. The expression and distribution of these two intranuclear pools of nucleolin was compared in estrogen receptor (ER)-positive and -negative invasive ductal breast carcinomas in relation to cell cycle phases. Materials and Methods: Using a laser scanning cytometer NU was measured within the whole nucleus, within nucleolin aggregates (NUA) and within the NUA-free karyoplasm. The G₁-, S- and G₂M-phase cell subpopulations were distinguished on DNA histograms. Results: The nuclei of ER-positive and ER-negative breast carcinomas in the G₂M-phase differed in the expression of NU in the NUA and in the NUA-free karyoplasm, whereas in the S-phase they only differed in the NUA-free karyoplasm expression. In ER-positive carcinomas NU levels rose from G₁ to G₂M in both the NUA and the NUA-free karyoplasm, whereas in ER-negative carcinomas the NU levels increased only between G₁/S in the NUA and between S/G₂M in the NUA-free karyoplasm. Conclusion: There are significant differences in nucleolin expression and localization during cell cycle progression depending on ER status.