Visit our Expo - Redox and Inflammation signaling 2012

Session XVII : Cell signaling in health and disease Poster XVII, 53
HSP90 INHIBITION BY GELDANAMYCIN UPREGULATES EXPRESSION OF
HEAT SHOCK PROTEINS IN PC-12 CELLS.
Christina B. Wiegand 1, Madhavi J. Rane3, Leroy R. Sachleben Jr 2, Rachel Wu 3 and
Evelyne Gozal 1,2
Depts of Pharm. & Tox.1, Pediatrics2, Medicine3, University of Louisville, Louisville,
KY
Heat shock proteins (Hsps) play a role in cellular injury, proteins repair and ubiquitination, or
induction of apoptosis when cells are beyond repair. Hsp90 regulates the function of its client
proteins and can bind Akt kinase or heat shock factor (HSF). Upon cellular stress HSF is
released to the nucleus to induce Hsps transcription. Geldanamycin (GA) binds Hsp90 ATPbinding
site, inhibiting its ATPase function and disrupting protein associations. We
previously showed that 6h sustained hypoxia (SH; 0.1% O2) increased Akt-Hsp90 binding
and Akt phosphorylation in PC-12 cells, without altering cell survival. However, 24h SH
decreased Akt phosphorylation, coinciding with the onset of cell death. GA induced cell death
and decreased Akt expression in a dose dependent manner, with higher toxicity in normoxia
(RA; 21% O2) than in SH, and disrupted Hsp90-Akt association without affecting SHinduced
Akt phosphorylation. Because of Hsps dual function in cellular repair and apoptosis,
we hypothesized that GA may affect cell survival by disrupting Hsp90 binding with
additional Hsps or with HSF. To determine whether GA modulates Hsps expression, GAtreated
cells were exposed to 6h, 12h, and 24h RA or SH. GA increased Hsp25, Hsp70 and
Hsp90 expression independently from FiO2, while Akt/Hsp90 binding was differentially
altered in SH and RA. Thus, increased Hsps expression observed in GA-treated PC-12 cells
may result from the dissociation of HSF from Hsp90 and its subsequent translocation
independently from the hypoxic stress. Increased Hsps expression may initially protect cells
from cytotoxic effects of low GA concentrations, as suggested by GA dose-dependent effect
on cell survival. However, longer GA exposures may increase cell death resulting from
accumulating damaged proteins or SH-related energy depletion. We are currently
investigating changes in HSF association with the Hsp90 complex in SH and RA GA-treated
cells. These findings suggest that disruption of Hsp90 chaperone functions by GA leads to
inactivation of survival pathways, alterations in the protein associations of Hsp90 complexes,
and induction of stress proteins targeting cells to apoptosis. NIH F30-NS051998-01, HL-
074296, 2 P20 RR15576-06, and AHA 0335278N.
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