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Human Embryonic Kidney 293 cells, also often referred to as HEK 293, HEK-293, 293 cells, or less precisely as HEK cells are a specific cell line originally derived from human embryonic kidney cells grown in tissue culture. HEK 293 cells are very easy to grow and transfect very readily and have been widely used in cell biology research for many years. They are also used by the biotechnology industry to produce therapeutic proteins and viruses for gene therapy.
HEK 293 cells were generated in the early 70s by transformation of cultures of normal human embryonic kidney cells with sheared adenovirus 5 DNA in Alex van der Eb's laboratory in Leiden, The Netherlands. The human embryonic kidney cells were obtained from a single apparently healthy fetus legally aborted under Dutch law; the identity of the mother and the reason for the abortion are no longer known. The kidney cells were originally cultured by van der Eb himself; the transformation by adenovirus was performed by Frank Graham in van der Eb's lab and were published in the late 1970s after Graham left Leiden for McMaster University in Canada. They are called HEK since they originated in human embryonic kidney cultures, while the number 293 comes from Graham's habit of numbering his experiments; the original HEK 293 cell clone was simply the product of his 293rd experiment.
Subsequent analysis has shown that the transformation was brought about by an insert consisting of ~4.5 kilobases from the left arm of the viral genome, which became incorporated into human chromosome 19.
For many years it was assumed that HEK 293 cells were generated by transformation of either a fibroblastic, endothelial or epithelial cell all of which are abundant in kidney. However the fact that the cells originated from cultured kidney cells does not say much about the exact cellular origin of the HEK 293, as embryonic kidney cultures may contain small numbers of almost all cell types of the body, including neural crest cells, neurons and glia. In fact Graham and coworkers more recently provided evidence that HEK 293 cells and several other human cell lines generated by adenovirus transformation of human embryonic kidney cells have many properties of immature neurons, suggesting that the adenovirus was taken up and transformed a neuronal lineage cell in the original kidney culture. As a consequence, HEK 293 cells may need to be re-characterized and should not be used as an in vitro model for kidney cell function or studies involving kidney cells.
HEK 293 cells have a very complex karyotype, exhibiting two or more copies of each chromosome and with a modal chromosome number of 64. They are described as hypotriploid, containing less than three times the number of chromosomes of a normal diploid human cell. Chromosomal abnormalities include a total of three copies of the X chromosome and four copies of chromosome 17 and chromosome 22. The presence of multiple X chromosomes and the lack of a Y chromosome suggest that the original fetus was female.
As an experimentally transformed cell line, HEK 293 cells are not a particularly good model for normal cells, cancer cells, or any other kind of cell that is a fundamental object of research. However, they are extremely easy to work with, being straightforward to culture and to transfect, and so can be used in experiments in which the behavior of the cell itself is not of interest. Typically, these experiments involve transfecting in a gene (or combination of genes) of interest, and then analyzing the expressed protein; essentially, the cell is used simply as a test tube with a membrane. The widespread use of this cell line is due to its extreme transfectability by the various techniques, including calcium phosphate method, achieving efficiencies approaching 100%.
An important variant of this cell line is the 293T cell line that contains, in addition, the SV40 Large T-antigen, that allows for episomal replication of transfected plasmids containing the SV40 origin of replication. This allows for amplification of transfected plasmids and extended temporal expression of the desired gene products. Note that any similarly modified cell line can be used for this sort of work; HeLa, COS and Chinese Hamster Ovary cell are common alternatives.
Examples of such experiments include:
A more specific use of HEK 293 cells is in the propagation of adenoviral vectors. Viruses offer an extremely efficient means of delivering genes into cells, since this is what they have evolved to do, and are thus of great use as experimental tools. However, as pathogens, they also present a degree of danger to the experimenter. This danger can be avoided by the use of viruses which lack key genes, and which are thus unable to replicate after entering a cell. In order to propagate such viral vectors, a cell line that expresses the missing genes is required. Since HEK 293 cells express a number of adenoviral genes, they can be used to propagate adenoviral vectors in which these genes (typically, E1 and E3) are deleted, such as AdEasy.
Depending on various conditions, the gene expression of HEK 293 cells may vary. The following proteins of interest (among many others) are commonly found in untreated HEK 293 cells:
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