BASIC SCIENCE: Prions in Yeast, Mice and Man

Applied Genetics News,  Feb, 2000  

• E-mail
• Print
• Link

Results from a number of laboratories have found some interesting properties of prions that may lead to treatments for prion- mediated neurodegenerative diseases such as Creutzfeld-Jacob disease and Alzheimer's disease. It has been found 1) that prions are modular proteins in which one module catalyzes amyloid plaque formation, and 2) that synthetic peptides can reverse plaque formation.

Axonyx, Inc. (825 Third Ave., 40th Floor, New York, NY 10022; Tel: 212/688-4770, Fax: 212/888-4843, Email: info@axonix.com Website: www.axonyx.com), in collaboration with researchers at the Serono Pharmaceutical Research Institute in Geneva and led by Claudio Soto, has shown that the appearance of clinical symptoms was significantly delayed in prion-infected mice treated with a synthetic peptide. This work was published in the January 14 issue of Lancet, and is the result of a research and development agreement with the Swiss biotechnology company Ares-Serono centering on peptide technology. The work has the potential to treat abnormal forms of protein accumulation in Mad Cow Disease, Creutzfeldt-Jakob disease, as well as Alzheimer's disease.

Degenerative diseases of the brain, such as Creutzfeld-Jakob disease, are characterized by the accumulation of an abnormal form of the prion protein, PrPSc, different from the normally occurring protein PrPC (sequence of 250 amino acids). The two PrP forms are very similar, except that regions of the altered prion show an abnormal folding, which is "infectious" in that it induces similar changes in otherwise normal prion proteins, leading to the accumulation of protein plaques that are damaging to the brain.

The Axonix/Serono study shows that the pathological change in shape of the prion protein can be reversed by treatment with a peptide (sequence of 13 amino acids) homologous to a small region of the prion protein. This treatment successfully reversed the abnormal structure of the prion protein to the normal form. In animal studies, the peptide breaker protein decreased infectivity by more than 90 to 95%.

"The ability of a rogue prion protein, without a genetic code, to become infectious and reproduce is a dramatic and revolutionary medical concept," states Marvin S. Hausman, M.D., president and CEO of Axonyx. "The proprietary prion inhibiting peptide technology offers a new therapeutic approach to controlling not only Mad Cow disease, but other diseases involving abnormal protein folding such as in Alzheimer's."

Researchers at the University of Chicago led by Susan Lindquist, in a Science (January 28 issue) paper, describe how prions can pass their particular conformation from one generation to the next without any change in DNA. In its "prion state" the protein can entice other, healthy proteins of the same kind to adopt the misfolded prion form, a kind of protein misfolding chain reaction. Additionally, prion states are both "infectious" and heritable-- they are passed from generation to generation with no change in the nucleic acid sequence.

Lindquist and postdoctoral fellow Liming Li demonstrate the creation of a novel prion by taking the prion-determining part of Sup35, a known yeast prion, and linking it to a mammalian hormone response factor to become prion-like. In a complimentary paper in the January issue of Molecular Cell, Lindquist and graduate student Neal Sondheimer describe a newly discovered yeast prion. "We already know that two of the 6,200 proteins in yeast can be prions," he says. "We wanted to know if there were more."

Sondheimer focused his search on a handful of suspect proteins that possessed regions that looked a lot like the prion- determining regions of known yeast prions Sup35 and Ure2. He used a fluorescent marker called GFP (green fluorescent protein) to label the suspected prion-determining domains of these proteins and looked to see if they aggregated in cells--a sign that they may be misfolding and an indication of prion-like activity. Four of the proteins he studied formed clumps in cells that appeared as large green fluorescent dots.

Sondheimer also looked at the effect of a heat-shock protein, Hsp104, on the proteins. One of the proteins, Rnq1, behaved exactly like a prion in its response to different concentrations of Hsp104. When Hsp104 was removed from the cell, Rnq1 aggregates disassociated. When Hsp104 was added back, Rnq1 formed clumps.

Finally, Sondheimer looked to see whether the prion state of Rnq1 could entice Rnq1 proteins in the normal state to switch to the prion state. "I exposed a cell that had soluble, or non-aggregated Rnq1 to Rnq1 in its misfolded prion state, and the cell would become infected--all the Rnq1 in that cell would be aggregated," he explains. Once he was convinced that Rnq1 was a prion, he took its prion-determining domain and switched it with that of Sup35. The new protein behaved exactly like Sup35. "The punch line of these two papers is that prions are modular," he says. "They are composed of regions that can be swapped with each other like Legos."