The Use of Nucleic Acid Aptamers to Inhibit the Uptake of Iron by Transferrin Receptors

Siri Manjunath, Transferrin Receptor, RNA N40B

The Use of Nucleic Acid Aptamers to Inhibit the Uptake of Iron by Transferrin Receptors

Abstract:

            Iron is found in both the body cells of humans and freely floating in blood plasma.¹ Most of the iron in the body is found in erythroid cells where it is used in the production of hemoglobin.¹ The transferrin receptor, along with its ligand, transferrin, play a pivotal role in the uptake of iron into human body cells. Additionally, transferrin receptors are also a focal point of targeted drug delivery as increased numbers of receptors are present on the surface of cancer cells and show high expression on the blood-brain barrier.²

Transferrin is a glycoprotein found in plasma that binds to iron and then attaches to the transferrin receptor on cell surfaces. This results in receptor mediated endocytosis, a process in which the transferrin and iron complex are engulfed into the cell in a vesicle.³ The iron then detaches from the transferrin and is available for the cell’s utilization.  In some cases, excessive levels of iron are taken into proliferating cells causing a decrease in the amount of iron present in the blood. This abnormality can be attributed to a malfunction of the IRE/IRP mechanism responsible for regulating transferrin receptors, where larger levels of iron in the plasma results in increased iron uptake by transferrin receptors and lower iron levels in the blood plasma results in decreased uptake.³

Though it is difficult to altogether prevent such a malfunction from occurring, the error can be dealt with in the manner of competitively preventing transferrin from binding its receptor. Such competitive binders can be found in the form of RNA aptamers that are specifically selected to bind to the transferrin receptor.

If these aptamers prove specific to the transferrin receptors, then they will competitively bind to the receptors thus preventing transferrin from binding and preventing iron from being absorbed into cells. This will compensate for the problem of increased iron uptake by the transferrin receptor meaning that there will be more iron present in the blood plasma. An application of such an aptamer could imply a possible solution for anemia, a condition in which there is a decreased amount of red blood cells and hemoglobin in the blood, a direct result of a deficiency in iron.  

Specific Aim 1: Perform SELEX to select for an aptamer that specifically binds to the transferrin receptor. Specific aptamer binding for the transferrin receptor is a diagnostic tool that would label cells that are rapidly dividing as rapidly dividing cells have more transferrin receptors. Additionally, an aptamer that binds specifically to the transferrin receptor would prevent iron-uptake into cells and keep iron levels stable in the blood plasma, and provide a solution to anemia.

Specific Aim 2: Perform in vitro analysis to determine whether the aptamer binds to transferrin receptor protein in place of the transferrin ligand.

                                    

Figure 1: The aptamer specific for the transferrin receptor will competitively bind to the receptor thereby preventing iron uptake into the cell and the effects of such increased iron uptake as well as providing a diagnostic tool for recognizing rapidly dividing cells. As the figure may not show up, here is a link to view it: http://www.google.com/imgres?um=1&hl=en&biw=1366&bih=667&tbm=isch&tbnid=U9SF4tMJsau1lM:&imgrefurl=http://www.umassd.edu/cas/chemistry/facultyampstaff/maolinguo/&imgurl=http://www.umassd.edu/media/umassdartmouth/chemistrybiochemistry/faculty/guo3.jpg&w=500&h=315&ei=Xd5GUJ_WLsTbyAHeooHQCg&zoom=1&iact=hc&vpx=177&vpy=163&dur=2722&hovh=178&hovw=283&tx=165&ty=118&sig=107027876474457036578&page=1&tbnh=123&tbnw=196&start=0&ndsp=20&ved=1t:429,r:0,s:0,i:73

Transferrin receptor (CAT # 30R-AT025) can be obtained at Fitzgerald Industries International (http://www.fitzgerald-fii.com/transferrin-receptor-protein-concentrate-30r-at025.html) at a price of $59.50 for 100ug.⁴

References:

1.      "Transerrin and Iron Transport Physiology." Information Center for Sickle Cell and Thalassemic Disorders. Harvard University, 29 Jan. 2001. Web. 06 Apr. 2012. <http://sickle.bwh.harvard.edu/iron_transport.html>.

2.      Wilner, Samantha E., Brian Wengerter, Keith Maier, Maria De Lourdes Borba Magalhães, David Soriano Del Amo, Supriya Pai, Felipe Opazo, Silvio O. Rizzoli, Amy Yan, and Matthew Levy. "An RNA Alternative to Human Transferrin: A New Tool for Targeting Human Cells." Nature (2012): 1-2. American Society of Gene and Cell Therapy, 2012. Web. 03 Sept. 2012. <https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2>.

3.      Ponka, P., and CN Lok. "The Transferrin Receptor: Role in Health and Disease." The International Journal of Biochemistry and Cell Biology 31.10 (1999): 1. Pubmed. Web. 3 Sept. 2012. <http://http://www.ncbi.nlm.nih.gov/pubmed/10582342>.

4.      "Transferrin Receptor Protein (concentrate) ( 30R-AT025 )." Transferrin Receptor Protein (concentrate). Fitzgerald Industries International, n.d. Web. 04 Sept. 2012. <http://www.fitzgerald-fii.com/transferrin-receptor-protein-concentrate-30r-at025.html>.
Full Proposal

This is the link to my first progress report: https://www.dropbox.com/sh/ysxasm5b3r15kws/0yn5tUdtmZ/Manjunath_Siri-Progress%20report%201.docx
This is the link to my second progress report:
https://www.dropbox.com/sh/ysxasm5b3r15kws/9Tw1GJfI6g/Manjunath_Siri-Progress%20report%202.docx
This is the link to my final report:
https://www.dropbox.com/sh/ysxasm5b3r15kws/loZEgdSn9h/Manjunath_Siri_FinalReport.docx