Figure 4. Withdrawal of BRAF^V600E expression leads to thyroid cancer cell apoptosis.

(A) Representative FFPE sections of thyroid tissues from Tg-rtTA/tetO-BRAF^V600E fed dox for 1 week (on) and then regular chow (off) for the indicated times, assayed by TUNEL (top) and cleaved caspase-3 (bottom). There was a modest increase in apoptotic cells at 1 week on dox, which were scattered throughout the thyroid tumor specimen. In contrast, the brown-red staining cells were localized within the center of the cancer cell clusters 72 hours after dox withdrawal. Original magnification, ×400 (top panels); ×400 (bottom panels). (B and C) Quantification of TUNEL and cleaved caspase-3 (+) cells at the indicated times. Data are shown as mean ± SEM and correspond to manual counting of 3 high-power fields/mouse (n = 6).