Characterization of distinct heat shock- and thapsigargin-induced cytoprotective proteins in FRTL-5 thyroid cells

Phosphorylation of heat shock protein-90 by TSH in FRTL-5 thyroid cells

CONTEXT

Although it is well established that thyrotropin (TSH) initiates signal transduction systems resulting in protein kinase(s) activation, the phosphorylated targets have not been fully characterized.

OBJECTIVE/DESIGN

In FRTL-5 thyroid cells, we used two-dimensional (2D) gel images of silver-stained proteins isolated from FRTL- 5 thyroid cells following TSH stimulation to identify potential phosphorylation targets.

RESULTS

We characterized a 90 kDa protein that had undergone a pH shift and subsequently identified it as heat shock protein-90 (hsp-90) following in-gel trypsin digestion and mass spectroscopy. This was confirmed by Western blot using a monoclonal antibody against hsp-90. Western blot analysis of the 2D gel images using a polyclonal antibody directed at phosphoserine/threonine sites showed that TSH induced the phosphorylation of hsp-90. Western blotting of hsp-90 following stimulators of the signal transduction systems mediated by TSH indicated that TSH-mediated hsp-90 phosphorylation occurs through protein kinases A and C.

CONCLUSION

In summary, we have demonstrated that TSH action stimulates the phosphorylation of hsp-90 in FRTL-5 thyroid cells. Abnormalities of hsp-90 phosphorylation may be a mediator in the development of thyroid disease.

N(omega)-nitro-L-arginine inhibits inducible HSP-70 via Ca(2+), PKC, and PKA in human intestinal epithelial T84 cells

The nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine (L-NNA) inhibits heat stress (HS)-induced NO production and the inducible 70-kDa heat shock protein (HSP-70i) in many rodent organs. We used human intestinal epithelial T84 cells to characterize the inhibitory effect of L-NNA on HS-induced HSP-70i expression. Intracellular Ca(2+) concentration ([Ca(2+)](i)) was measured using fura-2, and protein kinase C (PKC), and PKA activities were determined. HS increased HSP-70i mRNA and protein in T84 cells exposed to 45 degrees C for 10 min and allowed to recover for 6 h. L-NNA treatment for 1 h before HS inhibited the induction of HSP-70i mRNA and protein, with an IC(50) of 0.0471 +/- 0.0007 microM. Because the HS-induced increase in HSP-70i mRNA and protein is Ca(2+) dependent, we measured [Ca(2+)](i) after treating cells with L-NNA. L-NNA at 100 microM significantly decreased resting [Ca(2+)](i). Likewise, treatment with 1 microM GF-109203X or H-89 (inhibitors of PKC and PKA, respectively) for 30 min also significantly decreased [Ca(2+)](i) and inhibited HS-induced increase in HSP-70i. GF-109203X- or H-89-treated cells failed to respond to L-NNA by further decreasing [Ca(2+)](i) and HSP-70i. L-NNA effectively blocked heat shock factor-1 (HSF1) translocation from the cytosol to the nucleus, a process requiring PKC phosphorylation. These results suggest that L-NNA inhibits HSP-70i by reducing [Ca(2+)](i) and decreasing PKC and PKA activity, thereby blocking HSF1 translocation from the cytosol to the nucleus.