Figure 1.
Time- and concentration-dependent stimulation of autophagy by rapamycin.
A–B) Western-blot analysis for GAPDH and LC3 of protein lysates obtained from HeLa cells treated with DMSO or 1 µM rapamycin (Rapa) for the indicated time periods (A) (n = 7) or for 5 h with the indicated concentrations (B) (n = 6). One hour before harvesting, 100 nM bafilomycin A1 was added. Upper panels: representative Western blots; lower panels: quantification of the LC3-II/GAPDH ratio. C) GFP-LC3-punctae quantification in HeLa cells treated for 5 h with different concentrations of rapamycin. Left: representative pictures. The scale bar represents 10 µm. Concentrations are mentioned in the right lower corner. Right: Quantification of the number of punctae per cell (n = 3). * p<0.05, repeated measurements ANOVA.
Figure 2.
Rapamycin affects intracellular Ca2+ signaling.
A) Representative measurements (n = 4) of cytosolic Ca2+ signals, displayed as Fura2 ratio (F340/F380), showing the effect of 0.3 µM and 100 µM ATP, 1 µM thapsigargin (Tg) or 10 µM ionomycin (Iono) in intact HeLa cells treated with different concentrations of rapamycin (Rapa) for 5 h. 45 s prior to the addition of ATP, Tg or Iono, EGTA (3 mM) was given to buffer extracellular Ca2+ as indicated. B) Quantification of the average amplitude of the response (F−F0) (n = 4). * p<0.05; ** p<0.01; *** p<0.001, repeated measurements ANOVA. C) Mean resting cytosolic [Ca2+], measured in Fura2-loaded HeLa cells treated with the indicated concentrations of rapamycin for 5 h, as well as in the absence (Ctrl) or presence of DMSO (n = 3). * p<0.05, repeated measurements ANOVA. D) Unidirectional 45Ca2+-flux experiments in permeabilized cells pretreated with 1 µM rapamycin for 5 h or with DMSO (Ctrl). Mean fractional 45Ca2+ release (%/2 min) is shown as a function of time with the effect of 0.7 µM IP3 (circles) or no addition (squares). The horizontal bar indicates the presence of IP3. E) Quantitative analysis of the IP3-induced 45Ca2+ release in cells pretreated for 5 h with 1 µM rapamycin or DMSO (Ctrl) (n = 8). *** p<0.001, paired Student's t-test.
Figure 3.
Rapamycin reduces the ER Ca2+-leak rate.
A–B) Western-blot analysis for luminal Ca2+-binding proteins in HeLa cells treated with the indicated concentrations of rapamycin (Rapa) for 5 h: calreticulin (CRT) (A) and BiP/Grp78 (BiP) (B). Upper panels: representative Western blots; lower panels: quantification of the protein/GAPDH ratio (n = 4). C) Western-blot analysis for SERCA2 in HeLa cells treated with the indicated concentrations of rapamycin for 5 h. Upper panels: representative Western blots; lower panel: quantification of the SERCA2/GAPDH ratio (n = 4). D) Representative plot showing the decrease in ER 45Ca2+ content (logarithmic scale) in a Ca2+-free efflux medium without ATP as a function of time in permeabilized HeLa cells pretreated for 5 h with 1 µM rapamycin or with DMSO. The passively bound Ca2+ was determined by loading the cells with 45Ca2+ in the presence of 10 µM of the Ca2+ ionophore A23187 and then subtracted from the stored 45Ca2+. The ER Ca2+-leak rate can be estimated as the rate of decline of the ER 45Ca2+-store content as a function of time. E) Quantification of the mean 45Ca2+-store content at the beginning of the measurement (t0) (n = 5). F) Quantification of the mean slope of the curve in D after transformation to a linear scale, which is a measure of the 45Ca2+-leak rate (n = 5). * p<0.05; ** p<0.01, paired Student's t-test.
Figure 4.
Changes in Ca2+ signaling are independent of autophagy stimulation and occur upstream of the Atg12-Atg5 complex.
A) Representative Western-blot analysis for Atg12 (showing the autophagic Atg12-Atg5 complex), GAPDH and LC3 of protein lysates obtained from MEF cells pretreated with (+Dox) or without (-Dox) doxycycline and treated with DMSO or 0.1, 1 or 5 µM rapamycin (Rapa) for 5 h (n = 3). B–C) Representative measurements of cytosolic Ca2+ signals, displayed as Fura2 ratio (F340/F380), showing the effect of 1 mM ATP (B) or 10 µM ionomycin (Iono) in intact MEF cells pretreated with or without doxycycline and treated with different concentrations of rapamycin for 5 h. Prior to the addition of ATP or Iono, EGTA (3 mM) was added to chelate the extracellular Ca2+ as indicated. D) Quantification of the average amplitude of the response (F−F0) (n = 3, 4, 5 and 6 for ATP-Dox, ATP+Dox, Iono-Dox and Iono+Dox, resp.) * p<0.05; ** p<0.01; *** p<0.001, repeated measurements ANOVA.
Figure 5.
Rapamycin-induced autophagy is Ca2+-dependent.
Western-blot analysis for GAPDH and LC3 of protein lysates obtained from HeLa cells treated for 5 h with DMSO, 1 µM rapamycin (Rapa), 10 µM BAPTA-AM or both. One hour before harvesting, 100 nM bafilomycin A1 was added. Left: representative Western blots; right: quantification of the LC3-II/GAPDH ratio (n = 6). * p<0.05, repeated measurements ANOVA.