Figure 2.

Expression of ST18 is required for tumor maintenance. (A) Hemorrhages initiating from the tumor and extending to the adjacent subcutaneous areas were noticeable 4 hours after ST18 silencing and increased progressively throughout the indicated time course. All experiments were performed using induction of the shST18‐6 hairpin with administration of doxycycline (at time 0) by way of oral gavage. (B) Left: Ex vivo fluorescent imaging of tumors dissected from either untreated recipient mice or 24 hours after doxycycline administration. The fluorescent Venus marker was constitutively expressed from the same TtRMPVIR vector12 expressing doxycycline‐inducible shST18; loss of fluorescence after ST18 knockdown is thus due to loss of the targeted cells. Right: quantification of average radiant efficiency in the same tumors shown at left. **P = 0.0013. (C) Quantitative reverse‐transcription PCR analysis of ST18 mRNA levels in tumors confirmed knockdown 4 hours after shST18 induction. (D) Induction of shST18 induced hemorrhages and necrosis concomitant with a progressive decrease of ST18 expression. Insets denote that in untreated mice, the tumor was composed of highly cohesive atypical cells; in doxycycline‐treated tumors, cells were multifocally less cohesive, arranged in bundles, and spindle‐shaped. Scale bars = 100 μm.