Many neurodegenerative diseases are characterized by the accumulation of insoluble protein aggregates. In the case of prion related diseases it has been suggested that a conformational change in the prion protein (PrP) might constitute both the basis and maintenance of the diseased state. In an effort to understand how the normal prion protein (PrPC) is converted into its disease related isoform (PrPSc), neuroblastoma cells expressing either PrPC(N2a cells) or PrPSc (ScN2a cells) were examined for their expression of various molecular chaperones. The rationale being that molecular chaperones (many of which are heat shock proteins, hsp) are key components by which proteins acquire their final folded conformation in the cell, and therefore might participate in the conversion of PrPC to PrPSc. while both cell types expressed similar levels of the various molecular chaperones at their normal growth temperature, the ScN2a cells, in contrast to the N2a cells, were unable to mount a typical heat shock response as evidenced by their failure to express the two most highly induced hsp's, hsp 28 and hsp 72. Furthermore in only the ScN2a cells another hsp, hsp 73, was localized within discrete cytoplasmic aggregates and was largely resistant to extraction by nonionic detergents. Hence, we have established a possible connection between a disease hallmarked by the accumulation of an abnormally folded protein with that of a group of proteins, molecular chaperones, which participate in protein folding events.
Our specific aims now include; Determine whether similar alterations in the expression and/or locale of molecular chaperones is a general manifestation of different cell lines which propagate PrPSc; Delineate the basis underlying the observed cytoplasmic aggregates of the hsp 73 molecular chaperones observed in only the ScN2a cells; Decipher the mechanism by which transcription of hsp 28 and hsp 72 is inhibited in only the ScN2a cells; Investigate whether a similar inhibition of stress protein expression occurs in the brains of animals infected with PrPSc, and whether there exists similar large cytoplasmic aggregates of hsp 73 in the brains of infected animals; Examine in vitro whether purified molecular chaperones can affect the conversion of PrPC to PrPSc; Investigate the maturation of PrPC, and in particular define relevant molecular chaperones which participate in PrPC maturation and/or turnover in the N2a cells; and finally, identify possible components, such as molecular chaperones which might feature in the conversion of PrPC to PrPSc in various cell lines capable of propagating the PrPSc isoform. Such studies may reveal more clues regarding the cell biology and biochemistry of prion related diseases and the possible role of """"""""third parties,"""""""" for example molecular chaperones in the conversion of PrPC to PrPSc.
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