Antigen KI-67, also known as Ki-67, Ki-67 or MKI67 (Marker Of Proliferation Ki-67), is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

that in humans is encoded by the ''MKI67''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

(antigen identified by monoclonal antibody Ki-67).

Function

Antigen KI-67 is a nuclear protein that is associated with cellular proliferation. Altering Ki-67 expression levels did not significantly affect cell proliferation in vivo. Ki-67 mutant mice developed normally and cells lacking Ki-67 proliferated efficiently. Furthermore, it is associated with

ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...

transcription. Inactivation of antigen KI-67 leads to inhibition of ribosomal RNA synthesis.

Use as a marker of proliferating cells

The Ki-67 protein (also known as MKI67) is a cellular marker for proliferation, and can be used in

immunohistochemistry Immunohistochemistry (IHC) is the most common application of immunostaining. It involves the process of selectively identifying antigens (proteins) in cells of a tissue section by exploiting the principle of antibodies binding specifically to an ...

. It is strictly associated with cell proliferation. During

interphase Interphase is the portion of the cell cycle that is not accompanied by visible changes under the microscope, and includes the G1, S and G2 phases. During interphase, the cell grows (G1), replicates its DNA (S) and prepares for mitosis (G2). A c ...

, the Ki-67

antigen In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

can be exclusively detected within the

cell nucleus The cell nucleus (pl. nuclei; from Latin or , meaning ''kernel'' or ''seed'') is a membrane-bound organelle found in eukaryotic cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, h ...

, whereas in

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

most of the protein is relocated to the surface of the

chromosomes A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

. Ki-67 protein is present during all active phases of the

cell cycle The cell cycle, or cell-division cycle, is the series of events that take place in a cell that cause it to divide into two daughter cells. These events include the duplication of its DNA (DNA replication) and some of its organelles, and sub ...

(G₁, S, G₂, and mitosis), but is absent in resting (quiescent) cells (G₀). Cellular content of Ki-67 protein markedly increases during cell progression through S phase of the cell cycle. In breast cancer Ki67 identifies a high proliferative subset of patients with ER-positive breast cancer who derive greater benefit from adjuvant chemotherapy

Antibody labeling

Ki-67 is an excellent marker to determine the growth fraction of a given cell population. The fraction of Ki-67-positive

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

cells (the ''Ki-67 labeling index'') is often correlated with the clinical course of

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

. The best-studied examples in this context are

prostate The prostate is both an Male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, ...

, brain and

breast carcinoma Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a ...

s, as well as

nephroblastoma Wilms' tumor or Wilms tumor, also known as nephroblastoma, is a cancer of the kidneys that typically occurs in children, rarely in adults.; and occurs most commonly as a renal tumor in child patients. It is named after Max Wilms, the German surg ...

and neuroendocrine tumors. For these types of tumors, the prognostic value for survival and tumor recurrence have repeatedly been proven in uni- and multivariate analysis.

MIB-1

Ki-67 and MIB-1 monoclonal antibodies are directed against different epitopes of the same proliferation-related antigen. Ki-67 and MIB-1 may be used on fixed sections. MIB-1 is used in clinical applications to determine the ''Ki-67 labelling index''. One of its primary advantages over the original Ki-67 antibody (and the reason why it has essentially supplanted the original antibody for clinical use) is that it can be used on formalin-fixed paraffin-embedded sections, after heat-mediated antigen retrieval (see next section below). File:Positive immunohistochemistry of KI-67 in invasive breast cancer.jpg, High Ki-67 expression in an invasive

breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, milk rejection, fluid coming from the nipple, a newly inverted nipple, or a re ...

, with cancer nuclei being stained (brown). There is tumor cell positivity in 70% of the cells:
''Ki-67 labelling index'' = 70% File:Counting Ki-67 index in immunohistochemistry.jpg, Counting positive versus negative nuclei with Ki-67 labeling, in this case in a neuroendocrine tumor of the small intestine. To count as positive, a nucleus should be at least half within the field of view, be large enough, and not be located in the stroma. Otherwise, even weakly positive nuclei count as positive.

Original Ki-67 antibody

The Ki-67 protein was originally defined by the prototype monoclonal

antibody An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

Ki-67, which was generated by immunizing mice with nuclei of the

Hodgkin lymphoma Hodgkin lymphoma (HL) is a type of lymphoma, in which cancer originates from a specific type of white blood cell called lymphocytes, where multinucleated Reed–Sternberg cells (RS cells) are present in the patient's lymph nodes. The condition wa ...

cell line L428. The name is derived from the city of origin (

Kiel Kiel () is the capital and most populous city in the northern Germany, German state of Schleswig-Holstein, with a population of 246,243 (2021). Kiel lies approximately north of Hamburg. Due to its geographic location in the southeast of the J ...

, Germany) and the number of the original clone in the 96-well plate.

Interactions

Ki-67 (protein) has been shown to

interact Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...

with

CBX3 Chromobox protein homolog 3 is a protein that is encoded by the ''CBX3'' gene in humans. At the nuclear envelope, the nuclear lamina and heterochromatin are adjacent to the inner nuclear membrane. The protein encoded by this gene binds DNA and is ...

Additional images

File:Mouse NT antibody NF Ki67.jpg, Immunofluorescent antibody staining against neurofilament (green) and Ki-67 (red) in a mouse embryo 12.5 days after fertilization. The proliferating cells are in the ventricular zone in the

neural tube In the developing chordate (including vertebrates), the neural tube is the embryonic precursor to the central nervous system, which is made up of the brain and spinal cord. The neural groove gradually deepens as the neural fold become elevated, a ...

and therefore colored red. File:Ki-67 protein.jpg, Protein Ki-67 in human MCF-7 cells File:Ki67-Tubulin.jpg, Ki-67 protein (red),

tubulin Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytoske ...

(green) and DNA (blue) in HeLa cells. Dividing cells show strong Ki-67 staining in cell nuclei while all cells contain large amounts of tubulin, the major component of

microtubules Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 an ...

. Antibodies, cell staining and image courtesy of

EnCor Biotechnology EnCor Biotechnology is a United States company that manufactures monoclonal and polyclonal antibodies with a focus on reagents targeting neural proteins. EnCor was founded in 1999 as a spin-off from the University of Florida by Gerry Shaw, a ...

References

External links

* *http://www.pathologyoutlines.com/topic/stainski67.html * {{PDB_Gallery, geneid=4288 Cell biology Proteins Cell cycle