Figure 4.

FKBP51 stabilizes tau. A, HeLa cells stably overexpressing V5-tagged wild-type human tau were transiently transfected with FKBP51, FKBP52, or a vector control DNA harvested after 48 h. Western blot shows that FKBP51-transfected cells increase total tau (V5) and phospho-tau (pS212) compared to vector-containing cells. B, HeLa cells stably overexpressing V5-tagged wild-type human tau were transiently transfected with FKBP51, Flag Hsp90, and/or HA-ubiquitin. Co-IP with V5 antibody revealed that FKBP51 overexpression reduces ubiquitination of tau independent of Hsp90. C, HeLa cells stably overexpressing V5-tagged wild-type human tau were transiently transfected with FKBP51 plasmid or FKBP51 siRNA and tau was coimmunoprecipitated from these lysates after 48 h (for overexpression) or 72 h (for siRNA). Binding of endogenous Aha1 and P23, two well characterized Hsp90 cochaperones, was assessed. The association of Aha1 with tau was reduced or increased when FKBP51 was overexpressed or knocked down, respectively. P23 only associated with tau when FKBP51 was knocked down. Hsp90 binding to tau was increased by FKBP51 overexpression, and reduced slightly by FKBP51 knockdown. D, HeLa cells stably overexpressing V5-tagged wild-type human tau were transiently transfected with FKBP51 or empty vector for 48 h and treated with 100 nm okadaic acid (OA; +) or vehicle (−) for 30 min. Co-IP of these lysates with V5 antibody shows increased FKBP51 and Hsp90 binding to tau with OA treatment. Total tau levels were measured with anti-V5.