Cell expression of a four extra octarepeat mutated PrPC modifies cell structure and cell cycle regulation

RK13 cell lines generated to express bovine PrPC with a four extra octarepeat insertional mutation (Bo-10ORPrPC) show partially insoluble PrPC and lower rates of cell growth when compared to either the same cells expressing wild type Bo-6ORPrPC or the original RK13 cell line. The expression of Bo-10ORPrPC in cell cultures was also associated with changes in cell size and reorganization of the actin cytoskeleton. This last process was reversed by Clostridium difficile toxin-B, a specific inhibitor of small GTPase proteins. Further, in clones expressing Bo-10ORPrPC, increased proportions of cells at cell cycle stage G2/M were observed. Proteasome inhibitors caused a further expansion of G2/M-stage cells that was more marked in cell lines expressing Bo-10ORPrPC than those expressing Bo-6ORPrPC, while this effect was minimal or null in the original RK13 cell line. Hence, the presence of Bo-10ORPrPC in RK13 cells promotes cell cycle arrest at G2/M, and the effect is amplified by proteasome inhibition. These findings suggest a role for PrPC in cell morphology and cell cycle regulation, and open new avenues for understanding the mechanisms underlying PrP mutation-associated diseases.