Ki67

By Jamshed Arslan Pharm.D.

CD31/PECAM-1, or platelet endothelial cell adhesion molecule 1, is a 130-kDa glycoprotein expressed on vascular and hematopoietic cells.  Depending on the cell type, CD31/PECAM-1 expression can be largely localized to cell junctions, playing a role in cell adhesion.  Aside from its role in cellular adhesion, CD31/PECAM-1 is also a large player in a variety of signaling pathways, such as angiogenesis, cell migration, leukocyte transmigration and more.  Specifically, the association and indication of angiogenesis in breast cancer is of interest, given that extensive research shows an

Ki67, also known as MKI67, is best known as the leading marker of cellular proliferation. Ki67 is regulated by a balance between synthesis and degradation, and often carries a very short half-life.  First discovered to be located to dividing cells, Ki67 has since been specifically localized to the G1, S, G2 and M phases of mitosis. Soon after, it was discovered that there was a high correlation of Ki67 alongside the p53 (tumor suppressing protein 53), suggesting an implication in cancer. What’s more, the expression of Ki67 is higher in malignant cells versus control cells.

Ki-67/MKI67 is an antigen which is expressed during G1, S, G2, and M phases of the cell cycle (mitotically active cells), but not during G0 phase (resting cells). It is a large protein with expected molecular weight of about 395 kDa, and it has a very complex localization pattern within the nucleus, one which changes during cell cycle progression. During interphase, Ki-67 antigen can be exclusively detected in the nucleus, whereas in mitotic phase, most of Ki67 pool gets relocated to the chromosomal surface.

Keratins, also called cytokeratins, are a family of filamentous structural proteins that form the intermediate filaments within epithelial cells. Keratins are differentially expressed depending on both the epithelial cell origin and degree of differentiation. An antibody to any given keratin is useful either as a stand-alone or part of an antibody panel to help identify or clarify tissue origin. Cytokeratin 18 (CK18) is a 45 kD normal constituent of the hepatocyte cytoskeleton and is expressed in combination with cytokeratin 8.

The Ki67 antigen is a prototypic cell cycle-related protein expressed by proliferating cells in all phases of the active cell cycle (G1, S, G2 and M). It is a non-histone nuclear protein originally identified in a Hodgkin's lymphoma-derived cell line. Ki67 interacts with KIF15 and MKI67IP, and is approximately 395 kD. It exhibits a complex nuclear localization pattern that is cell cycle-dependent - expression peaks during late G1, S, G2, and M phases, but is undetectable in G0.

The MK167, or Ki67 antibody recognizes a nuclear protein encoded by the MK167 gene. Ki167 is involved with RNA transcription and essential to cellular proliferation, being expressed by proliferating cells at all stages of the active cell cycle; it is exclusively used as a marker for cellular proliferation.