The membrane-associated transient receptor potential vanilloid channel is the central heat shock receptor controlling the cellular heat shock response in epithelial cells

Abstract

The heat shock response (HSR) is a highly conserved molecular response to various types of stresses, including heat shock, during which heat-shock proteins (Hsps) are produced to prevent and repair damages in labile proteins and membranes. In cells, protein unfolding in the cytoplasm is thought to directly enable the activation of the heat shock factor 1 (HSF-1), however, recent work supports the activation of the HSR via an increase in the fluidity of specific membrane domains, leading to activation of heat-shock genes. Our findings support the existence of a plasma membrane-dependent mechanism of HSF-1 activation in animal cells, which is initiated by a membrane-associated transient receptor potential vanilloid receptor (TRPV). We found in various non-cancerous and cancerous mammalian epithelial cells that the TRPV1 agonists, capsaicin and resiniferatoxin (RTX), upregulated the accumulation of Hsp70, Hsp90 and Hsp27 and Hsp70 and Hsp90 respectively, while the TRPV1 antagonists, capsazepine and AMG-9810, attenuated the accumulation of Hsp70, Hsp90 and Hsp27 and Hsp70, Hsp90, respectively. Capsaicin was also shown to activate HSF-1. These findings suggest that heat-sensing and signaling in mammalian cells is dependent on TRPV channels in the plasma membrane. Thus, TRPV channels may be important drug targets to inhibit or restore the cellular stress response in diseases with defective cellular proteins, such as cancer, inflammation and aging.

Figure 1. Capsaicin and capsazepine effects on heat shock protein expression in HEK293e, MLE-12, MCF-7 and HT-29 cells.

Representative immunoblot analysis of Hsp70, Hsp90 and Hsp27 abundances. Hsp70, Hsp90 and Hsp27 were detected in HEK293e (Panel A), MLE-12 cells (Panel B), HT-29 (Panel C) and MCF-7 (Panel D). Cells in culture were incubated with 0.01% DMSO, 32 µM of capsaicin (Caps) for 1 hr, 32 µM of capsaicin (Caps) for 1 hr with the addition of 100 µM capsazepine (CPZ) or 100 µM capsazepine alone at 37°C. Cells were treated with either heat shock at 42°C for 3 hrs, heat shock at 42°C for 3 hrs with the addition of 100 µM capsazepine. Cells were treated with 32 µM of capsaicin with the addition of 5 mM EGTA, 5 mM EGTA alone at 37°C or heat shock at 42°C for 3 hrs with the addition of 5 mM EGTA. 15 µg of total protein/lane were separated on 9% SDS-PAGE gel.

Figure 2. TRPV1 mRNA and protein abundances in HEK-293e cells.

A. Semi-quantitative RT-PCR for TRPV1. Upper left panel: mRNA levels from PC3 prostate cancer cells: non treated cells, cells treated with 32 µM capsaicin for 1 hr and cells treated with heat shock at 42°C for 3 hrs. Lower right panel: mRNA levels of GAPDH as well as densitometric. Upper right panel: mRNA levels from HEK-293e cells: non treated cells, cells treated with 32 µM capsaicin for 1 hr (Caps), cells treated with heat shock at 42°C for 3 hrs, and cells treated with heat shock at 42°C for 3 hrs with the addition of 32 µM capsaicin. Lower right Panel: mRNA levels of GAPDH as well as densitometry. B. Representative immunoblot analysis of TRPV1 abundance. TRPV1 was detected in HEK-293e cells. Cells in culture were incubated with 0.01% DMSO or treated with 4 µM, 16 µM or 32 µM of capsaicin for 1 hr. C. Representative immunoblot analysis of TRPV1 and Hsp90 abundances in HEK-293e cells. Cells were treated with 32 µM capsaicin for 0 hr, 1 hr, 4 hrs and 6 hrs.

Figure 3. Capsazepine inhibits HSF-1 expression and nuclear translocation.

A. Representative immunoblot analysis of nuclear HSF-1 and phospho-HSF-1 abundances. Intra-nuclear HSF-1 and Phospho-HSF-1 were detected in HEK-293e cells. Cells were incubated with 4 µM, 16 µM or 32 µM of capsaicin for 1 hr. HEK-293e cells were treated as indicated with heat shock at 42°C for 3 hrs, heat shock at 42°C for 3 hrs with the addition of 5 mM EGTA, heat shock at 42°C for 3 hrs with the addition of 100 µM capsazepine or 100 µM capsazepine with the addition of capsaicin. B. Semi-quantitative RT-PCR for HSF-1. Upper panel: mRNA levels from non treated HEK293e cells (control), cells treated with 32 µM capsaicin for 1 hr (Caps), cells treated with heat shock at 42°C for 3 hrs, cells treated with heat shock at 42°C for 3 hrs with the addition of 100 µM capsazepine. Lower Panels: GAPDH mRNA levels from HEK293e cells as indicated above as well as densitometric analysis (Right panel). C. Electrophoretic mobility shift assay for HSF-1 DNA binding activity. Nuclear protein isolated from HEK-293e cells treated with 4 µM, 16 µM or 32 µM of capsaicin for 1 hr. Cells treated as indicated with heat shock at 42°C for 3 hrs, heat shock at 42°C for 3 hrs with the addition of 5 mM EGTA, heat shock at 42°C for 3 hrs with the addition of 100 µM capsazepine or 100 µM capsazepine with the addition of capsaicin. 10 µg of nuclear protein incubated for 20 min at room temperature with a ³²P-labeled double-stranded DNA oligonucleotide containing a consensus –HSF-1 binding site. Right panel indicates densitometric analysis.

Figure 4. Effect of various TRPV1 agonists and antagonists on heat shock protein expression.

A. Capsaicin & Capsazepine: Representative immunoblots analysis of Hsp70, Hsp90 and Hsp27 abundances. Hsp70, Hsp90 and Hsp27 were detected in MLE-12 (Panel a), HEK-293e (Panel b) cells. Hsp70 was detected in Cells in L3 – primary cells isolated from human lung tumors (Panel d). Cells culture were incubated with 0.01% DMSO, 4 µM, 16 µM or 32 µM of capsaicin (Caps) for 1 hr. 15 µg of total protein/lane were separated on 9% SDS-PAGE gel. (Panel c) represents Hsp70 and Hsp90 levels in control HEK-293e cells, HEK-293e cells treated with 32 µM of capsaicin for 1 hr, heat shock treatment for 3 hrs at 42°C and cells treated with both 32 µM of capsaicin for 1 hr and heat shock for 3 hrs at 42°C.B. RTX & AMG-9810: Representative immunoblot analysis of Hsp70, Hsp90. Hsp70, Hsp90 were detected in MLE-12 and HT-29 cells. Cell cultures were incubated with 0.01% DMSO, 10 nM, 40 nM, 50 nM or 80 nM of RTX for 1 hr, 80 nM RTX with the addition of 5 µM of AMG-9810 for 1 hr, 5 µM AMG-9810 at 37°C for 1 hr or 10–50 µM AMG-9810 at 42°C for 3 hrs. 15 µg of total protein/lane were separated on 9% SDS-PAGE gel.

Figure 5. TRPV1 expression in HEK293e cells.

A. Left panel: Double immunofluorescence staining of TRPV1 and Hsp70 in HEK-293e cells treated with 32 µM capsaicin for 1 hr. TRPV1 visualized in green, Hsp70 in red and DAPI (Nuclei) in blue. White arrows indicate Hsp70 abundance (left picture) and co-localization (right picture). B. Right panel: Immunofluorescence staining of Hsp70 in HEK-293e cells in non-treated cells, treated cells with 32 µM of capsaicin for 1 hr, heat shock treated cells for 3 hrs at 42C and cells transfected with 200 nM TRPV1 siRNA and treated with heat shock for 3 hrs at 42C.

Figure 6. HEK293e cells versus HEK cells and S2 KO cells – TRPV1 & TRPV4 expressions.

A. Representative immunoblot analysis of Hsp70 and TRPV1 in HEK with or without the transfection of the TRPV1 gene (HEK, HEK+V1) and S2 drosophila cells lacking the TRPV1 gene (S2). B. Semi-quantitative RT-PCR for TRPV4. Upper panel: mRNA levels from HEK and PC3 prostate cancer cells: non treated cells (DM), cells treated with 32 µM capsaicin for 1 hr (Cps) and cells treated with heat shock at 42°C for 3 hrs (HS) or with heat shock at 42°C for 3 hrs with the addition of capsaicin (Cps+HS). Lower panels: mRNA levels from HEK-293e cells: non treated cells (DM), cells treated with 32 µM capsaicin for 1 hr (Cps), cells treated with heat shock at 42°C for 3 hrs (HS), and cells treated with heat shock at 42°C for 3 hrs with the addition of 32 µM (Cps+HS) and mRNA levels of GAPDH.

Figure 7. TRPV1 membrane receptor activates the HSR.

A. Hsp70 co-localized in MCF-7 cell membrane. Immunofluorescence staining of Hsp70 in MCF-7 cells treated with 32 µM capsaicin for 1 hr. Hsp70 visualized in red and DAPI (Nuclei) in blue. White arrows indicate co-localization of Hsp70 to the membrane (right picture). B. Hsp70 expression in MCF-7 cells. Immunofluorescence staining of Hsp70 in MCF-7 cells in non treated cells compared to treated cells with 32 µM capsaicin for 1 hr. C. TRPV1 expression in lung homogenate in vivo. Representative immunoblot analysis of TRPV1 and Hsp70 abundances. TRPV1 and Hsp70 were detected in lungs of untreated rats (T0), septic rats treated with PBS (2CLPPBS) or septic rats treated with adenovirus vector over-expressing Hsp70 (2CLPAdHSP). The numbers (1, 2) represent repeated experiments. D. Co-IPs studies in lung homogenates treated with adenoviral vector over-expressing Hsp70 in-vivo. 100 µg of lung homogenates were Co-IPed with TRPV1. Representative immunoblot analysis of TRPV1 and Hsp70 abundances.

Figure 8. TRPV1 siRNA assay.

Upper panels: A. TRPV1 siRNA – sequence No. 1: Knockdown of TRPV1, using siRNA, in HEK-293 and HT-29 cells resulted in inhibition of Hsp90, and Hsp70 expression. HEK293 & HT-29 cells were treated with either oligofectamine alone, heat shock at 42°C for 3 hrs, heat shock at 42°C for 3 hrs with the transfection of 100 nM TRPV1 siRNA or with the transfection of 200 nM TRPV1 siRNA. Cells were transfected with TRPV1 siRNA for 72 hrs, prior to heat shock. Lanes grouped by curly brackets represent repeated RNAi experiments. B. TRPV1 siRNA – sequence No. 2 & scrambled siRNA: Knockdown of TRPV1, using a second sequence of siRNA and 200 nM of scrambled siRNA in HEK-293 and HT-29 cells, resulted in inhibition of Hsp90, and Hsp70 expression.Lower panel: Representative immunoblot of TRPV1 abundance. TRPV1 was detected in HEK-293 cells treated with heat shock at 42°C for 3 hrs with the transfection of either 100 nM TRPV1 siRNA or 200 nM TRPV1 siRNA. Lanes grouped by curly brackets represent repeated RNAi experiments.