Proliferation Marker Antibodies

Introduction

Ki-67

The Ki67 is a 360 kD protein and the prototypic cell cycle related nuclear protein, expressed by proliferating cells in all phases of the active cell cycle (G1, S, G2 and M phase). It is absent in resting (G0) cells. In G1 phase the Ki-67 antigen is predominantly localized in the perinucleolar region, in the later phases of the cell cycle the antigen is also detected throughout the nuclear interior, being predominantly localized in the nuclear matrix. In mitosis, the Ki-67 antigen is present on all chromosomes and appears in a reticulate structure surrounding the metaphase chromosomes. Because Ki-67 immunostalning rapidly decreases during anaphase and telophase, it has been concluded that the antigen is degraded with a biological half-life of the detectable antigen of less than one hour, as estimated in postmitotic cells during stathmokinesis induced by vinblastine. In contrast to many other cell cycleassociated proteins like PCNA, the Ki-67 antigen is consistently absent in quiescent cells and is not detectable during DNA repair processes. Thus, the presence of the Ki-67 antigen is strictly associated with the cell cycle and confined to the nucleus, suggesting an important role of this structure in the maintenance and/or regulation of the cell division cycle.

PCNA

Expression of the 36 kD proliferating cell nuclear antigen (PCNA) is elevated in the nucleus during late G1 phase immediately before the onset of DNA synthesis, becoming maximal during S-phase and declining during G2 and M phases. Its level correlates directly with rates of cellular proliferation and DNA synthesis. PCNA may act as an auxiliary protein of DNA polymerase-delta to play a fundamental role in the initiation of cell proliferation. A major drawback for PCNA as a proliferation marker for diagnostics is the fact that it is also detectable in almost all quiescent cells adjacent to some tumors and, presumably due to its long biological half-life, is also noticed in many quiescent tumor cells of different entities. A possible reason for the occurrence of PCNA in quiescent cells is its involvement, together with enzymes of the DNA replication machinery, in nucleotide excision repair mechanisms, as demonstrated in quiescent cells after ultra-violet irradiation in vitro and in vivo.

p105

The p105 protein, found in all human cells in a dimeric form (105 kD) and monomeric form (41 kD), is a proliferation-associated nuclear antigen that is absent in non-cycling cells in the G0 phase. This protein is important in the synthesis and transport of RNA in the cell regulation cycle. During G2 and mitosis, this protein is increased possibly due to the unmasking of nucleolar antigens, resulting in large accumulations of this protein in the mitotic cytoplasm.

IPO-38

IPO-38 antigen is present in the nuclei of proliferating cells such as Hodgkin’s disease and non-Hodgkin’s lymphomas, different forms of leukemias, breast and colorectal carcinomas, and PHA-stimulated lymphocytes. It is not expressed in the cells of non-stimulated lymphocytes and granulocytes. IPO-38 can be a useful marker of cell proliferation during monitoring of tumor progression.

Antibody Tools for Detection of Proliferating Cells

Antibodies are available for all markers listed above. These products are suitable for various applications like immunhistochemistry, Western blotting, immunoprecipitation or ELISA.

Fig.1: Staining of human small intestine using SM1421P PCNA antibody on paraffin sections

Fig.2: Staining of human tonsil using R1174 IPO-38 antibody on paraffin sections

Available Antibody Panel to Proliferation Markers

Anti- Ki-67 (Ki67), PCNA (Proliferating Cell Nuclear Antigen), p105 (Proliferation Associated Nuclear Antigen, PANA) , IPO-38 (IPO38)