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. 2011 Sep 12;6(11):1198–1204. doi: 10.1021/cb200292c

Figure 4.

Figure 4

(a) Protection of a destabilized variant of HRP (apo-HRP) and stable wild-type HRP (wt-HRP) from degradation by macrophage lysosomes (6 h incubation at 37 °C; pH 4.5). Inhibitors added as indicated at a final concentration of 5 μM. Only CPI protects the unstable variant apo-HRP (lane 4). Cystatin C (lane 3) and pepstatin A (lane 5) offer only partial protection against degradation of this destabilized protein. wt-HRP is largely stable in the presence of macrophage lysosomes (lanes 7–11). (b) CPI arrests EGF receptor downregulation and sustains signaling. COS7 cells were stimulated with EGF for up to 90 min following a preincubation in the presence or absence of CPI or cystatin C (15 μM final concentration). The downregulation of the EGF receptor (top panel) was assayed by Western blotting along with levels of phospho-Erk1/2 (p42/44 MAP kinase; bottom panel) and Rsk2 to assess total cellular protein loading (middle panel). (c) EGFR abundance throughout the treatment time course relative to t = 0 (left panel); phosphorylated p42/44 abundance throughout the treatment time course relative to t = 20 min (right panel).