Isolating and Characterizing the mRNAs That Bind FMRP

With $60,000 in grants from FRAXA Research Foundation from 1998-1999, Dr. Robert Denman and his team at the New York State Institute for Basic Research explored how how FMRP possibly functions.

Robert Denman, PhD
$60,000 Grant

Robert Denman, PhD
Principal Investigator

Natalia Dolzhanskaya, PhD
FRAXA Postdoctoral Fellow

New York State Institute for Basic Research
1998-1999 FRAXA Research Grant
$60,000 over 2 Years 

by Robert Denman, 1/1/2003

All cells are composed of a variety of specialized structures and compartments. These structures and compartments perform the myriad of functions that we define as living. The master plan for each cell, that is, the general instructions that must be carried out for the cell to “live” and the auxiliary instructions it must carry out to perform specialized functions, is encoded in the cell’s genetic information (DNA). For cells to perform these tasks, the genetic information is copied into messages (mRNA) that are in turn translated into proteins, which actually do the functioning.

We have identified some of the messages that may be responsible for the diverse behavioral features of Fragile X syndrome. These messages bind to the protein FMRP, the Fragile X mental retardation protein, which is absent in people with this syndrome. We call these messages the targets of FMRP.

We have gone on to show in several select cases that FMRP acts as a restrictor valve on the cell’s protein synthesis machinery to regulate the normal levels of the proteins produced from these messages. When FMRP is present, the messages are fed slowly through the restrictor, and the corresponding proteins are made in low to moderate amounts. In the absence of FMRP, much greater amounts of the proteins are produced. Because protein levels are finely balanced, or tuned, in cells to orchestrate the many functions they perform, too much or too little of a particular protein may not be beneficial. FMRP alone may regulate more than 500 messages; therefore, its loss causes a significant disturbance to the normal balance of proteins.

We are attempting to answer the questions:

  • How does FMRP bind particular messages? Since not all messages bind to FMRP, what enables this protein to bind one message and not another?
  • Do the interactions between FMRP and these messages change over time, and if they do, what is responsible for these changes?
  • How do the answers to the above two questions add to our understanding of the role FMRP plays in cells? Can we make a model of how FMRP works that will allow us to predict what is going wrong in individuals with Fragile X syndrome?

We have found that two proteins (called PRMT and CK2) that communicate signals from outside the cell to information processing centers inside the cell can modify one of FMRP’s message-binding sites and, in so doing, influence its ability to regulate the messages it binds.

No one before has ever modified FMRP in cells and found that doing so changes its basic properties. We have shown that altering one of FMRP’s message binding sites dictates whether a particular message binds to it. Our results provide a framework for understanding how FMRP functions, i.e., how specific messages interact and are regulated.

Now that we know that PRMT and CK2 can potentially modify several sites in FMRP, we must identify which of these sites is the major site of modification and determine whether it changes when cells are perturbed in different ways.
REFERENCE

Sung, Y-J., Dolzhanskaya, N., Nolin, S., Brown, W. T., and Denman, R.B.: The Fragile X Mental Retardation Protein FMRP Binds Elongation Factor lA mRNA and Negatively Regulates its Translation in vivo. (2003) Journal of Biological Chemistry 278, 15669-15678.

Dolzhanskaya, N., Merz, G., Aletta, J., and Denman, R. B.: Methylation Regulates its Intracellular Protein-Protein and Protein RNA Interactions of FMRP. (2006) Journal of Cell Science 119, 1933-1946.

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