What is Cyclin-Dependent Kinase?

Karyn Maier
Karyn Maier

Cyclin-dependent kinase, or CDK, is a type of enzymatic protein that resides in eukaryotic cells and plays a key role in cellular metabolism and renewal, a series of biological processes collectively referred to as the cell cycle. Several protein kinases are also classified as genes, making up about 2 percent of all human genes. The mechanism of CDK activity is based on phosphorylation, or the process of contributing phosphate groups to substrate proteins. However, in order for a protein to be modified by phosphorylation, it must form a complex with another kind of protein known as cyclin. This is why this particular specialized protein is termed cyclin-dependent kinase.

The majority of kinases select the amino acids serine and threonine.
The majority of kinases select the amino acids serine and threonine.

Aside from regulating cellular function, the other significant activity associated with cyclin-dependent kinase is providing the pathway for signal transduction. In other words, cells are able to communicate with each other by enlisting CDK enzymes to serve as chemical messengers. While this process may be fascinating to biology enthusiasts, it is of primary interest to the medical community due to its implication in the development of disease. In fact, impaired signal transduction is considered largely responsible for the onset of many diseases, including heart disease, diabetes, cancer, and many auto-immune disorders.

Inhibiting certain CDK proteins may help prevent the hair loss often associated with chemotherapy.
Inhibiting certain CDK proteins may help prevent the hair loss often associated with chemotherapy.

One of the most promising applications regarding the treatment of such diseases is the possibility of intercepting cyclin-dependent kinase activity in cells. In fact, a few medications designed to target and inhibit CDK have been shown to promote apoptosis, or cellular death. This result is particularly significant in terms of combating tumor growth and the spread of cancer. In addition, these drugs appear to affect neutrophil granulocytes, which contribute to the development of chronic inflammatory conditions such as arthritis. However, since these drugs may also impact the cyclin-dependent kinase mediated pathway and lead to unwanted side effects, more research is needed to ensure only receptor cells are targeted.

There are also different kinds of CDK proteins that may be targeted to help prevent a variety of reactions. For example, inhibiting cyclin-dependent kinase 2 may help to deter hair loss that often occurs while being treated with chemotherapy, while manipulating cyclin-dependent kinase 4 may impact the regulation of Rb, a protein linked to tumor suppression.

Protein kinases also work differently toward cellular regulation. While each type initiates phosphorylation by borrowing a phosphate group from adenosine-5-triphosphate (ATP), it must also be able to attach the phosphates to an available hydroxyl group belonging to one of three amino acids. The majority of kinases accomplish this by selecting the amino acids serine and threonine, while others seek out tyrosine. However, there are a few that are compatible with all three.

Karyn Maier
Karyn Maier

Contributing articles to wiseGEEK is just one of Karyn’s many professional endeavors. She is also a magazine writer and columnist, mainly for health-related publications, as well as the author of four books. Karyn lives in New York’s Catskill Mountain region and specializes in topics about green living and botanical medicine.

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Discussion Comments


It's interesting that there are drugs out there that combat tumors by basically causing cellular death of cyclin-dependent kinase. I'm not surprised that these medicines can lead to unwanted side effects though.

It seems like cyclin-dependent kinase has a bunch of different functions and affects a lot of different processes. So if you're going to try and treat a disease by using a medication that affects cyclin-dependent kinase, it makes sense that it would need to be very specifically targeted. Obviously you don't want to get rid of all the cyclin-dependent kinase in the body!


@JaneAir - It is sometimes hard to retain knowledge after you take a class. Unless you're using what you've learned, you're very likely to forget! I too have some memory of learning about cyclin-dependent kinase in school.

I think the thing that really stuck out to me about these proteins is the role they play in disease, like the article said. It's amazing how if one small thing in a cell goes wrong, you can end up with some terrible disease, like a heart disease or an autoimmune disorder.

However, at least they're able to use cyclin-dependent kinase inhibitors to counteract some of these effects. I think it's neat that they've thought to use a cyclin dependent kinase inhibitor to help prevent hair loss from chemotherapy.


I vaguely remember learning about cyclin-dependent kinase and cyclin-dependent kinase inhibitors when I took biology. Let me just say, cells are extremely complex and there was a lot to remember! I probably learned and forgot more stuff in that class than in any other class.

Anyway, let me just point out the eukaryotic are complex cells. So, humans and mammals have eukaryotic cells. There is another type of cell called a prokaryotic cell that is far less complex. As the article said, cyclin-dependent kinase exists in eukaryotic, but not in less complex cells.

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