Erythropoietin
Extra credit report (699 word count)
Introduction to Biochemistry
Michael Prentice
April 26, 2017
Erythropoietin (EPO) is naturally occurring protein hormone the body uses every day, however, its abuse
in synthetic form is a type of blood doping that has been the subject of many recent sporting fraud
cases, most notably, multiple Tour de France winner Lance Armstrong, but has also been abused in other
sporting venues, particularly the Olympic games (1).
Erythropoietin is a type I cytokine protein hormone which is created primarily in the kidney but also less
so in the liver (2). Endogenous EPO was first isolated in 1977, and its gene was first cloned in 1985.The
gene for human erythropoietin is located at chromosome 7q11-22. It is composed of four introns and
five exons, resulting in a post-transcriptional single polypeptide of 193 amino acids. This single amino
acid backbone undergoes post-translational modification whereby one O-glycosylation and three
N-glycosylation sites are added and 28 amino acids are removed. This results in the final primary
structure of mature EPO containing 165 amino acids in a polypeptide chain with a molecular mass
estimated to be 30 kilodaltons (3).
EPO primary structure (4)
EPO folds into a globular three-dimensional structure consisting of four amphipathic α helices connected
by loops that lack secondary structure. The structure is stabilized by a disulphide bridge between the
amino-terminal and carboxy-terminal helices (5).
EPO ribbon structure (6)
EPO acts on erythrocytes, commonly known as red blood cells, which are disc-shaped cells that are
responsible for carrying oxygen via embedded hemoglobin throughout the body (7). When oxygen is
inhaled through the lungs, it is delivered to red blood cells and carried to cells for use in metabolism, and
the resulting carbon dioxide is then returned to the lungs for exhalation via the same red blood cells (8).
Erythrocyte (9)
Red blood cells are created in the bone marrow and in order to manufacture these red blood cells the
body uses EPO. EPO specifically targets erythroid progenitors in the bone marrow to cause maturation
into erythrocytes (3). EPO is a component of blood plasma and has a half-life of approximately 7 to 8
hours. It binds to receptors that are present in relatively small numbers (approximately 1000/cell) on the
surface of the erythroid progenitor cells. The EPO signal transduction pathway follows the classical
transduction pathway where EPO binds to an EPOR homo-dimer leading to activation of the signaling
cascade. The main signaling pathways activated by EPO are the JAK2/STAT5 pathway, protein kinase C
(PKC) pathway, RAS/MAP kinase pathway, and the phosphatidylinositol 3-kinase (PI3K) pathway (10).
EPO transduction pathway (10)
If the body does not create enough red blood cells, a condition called anemia ensues. Anemia can be
caused by several factors, one of which is low EPO production. An artificially synthesized form of EPO,
recombinant erythropoietin, can be administered via injection in patients suffering from anemia.
Recombinant erythropoietin is categorized as an erythropoietin-stimulating agent (ESA). Patients
undergoing chemotherapy or suffering from renal (kidney) failure are the most common recipients of
this drug, although other patients, such as those who refuse blood transfusions, also receive EPO
treatments (8).
EPO – erythrocyte cycle (11)
Similar to anemic patients, athletes use EPO in order to increase the number of oxygen carrying
erythrocytes circulating in their body. This increases their ability to metabolize the delivered oxygen and
gives them an unfair advantage over their competition (12).
References
1.
doping-technology (Accessed April 26, 2017)
2. (Accessed April 26, 2017)
3. John, M. J., Jaison, V., Jain, K., Kakkar, N., & Jacob, J. J. (2012). Erythropoietin use and abuse. Indian
Journal of Endocrinology and Metabolism, 16(2), 220–227.
4. Lappin, T. (2003). The Cellular Biology of Erythropoietin Receptors. The Oncologist 2003; 8:15-18;
doi:10.1634/theoncologist.8-suppl_1-15
5. Bunn, H. F. (2013). Erythropoietin. Cold Spring Harbor Perspectives in Medicine, 3(3), a011619.
6.
ime (Accessed April 26, 2017)
7. (Accessed April 26, 2017)
8. (Accessed April 26,
2017)
9. (Accessed April 26, 2017)
10. Debeljak, N., Solár, P., & Sytkowski, A. J. (2014). Erythropoietin and Cancer: The Unintended
Consequences of Anemia Correction. Frontiers in Immunology, 5, 563.
11.
(Accessed April 26, 2017)
12. (Accessed April 26, 2017)
