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. Author manuscript; available in PMC: 2013 Jul 15.
Published in final edited form as: Clin Cancer Res. 2012 May 15;18(14):3889–3900. doi: 10.1158/1078-0432.CCR-11-3182

Figure 4. DARPP-32 promotes TRAIL resistance by up-regulating BCL-xL through activation of Src/STAT3 signaling.

Figure 4

A) Two clones of MKN-28/DARPP-32 and MKN-28/pcDNA3 cells were treated with vehicle, 200 ng/ml TRAIL, TRAIL in combination with 5 µM PP1, a specific Src inhibitor, or PP1 alone for 24h and subjected to clonogenic survival assay. B) The quantification of surviving colonies indicated that DARPP-32 significantly promoted cell survival in response to TRAIL, as compared to control. However, as shown, TRAIL in combination with PP1 completely reversed the effect of DARPP-32 on cell survival. C) MKN-28/DARPP-32 and MKN-28/pcDNA3 cells were treated with vehicle, TRAIL, TRAIL in combination with PP1, or PP1 as described in panel A. qRT-PCR results showed that BCL-xL mRNA level was significantly higher in DARPP-32-expressing cells than in control cells, following treatment with vehicle (p<0.01) or TRAIL (p<0.001), respectively. However, treatment with PP1 alone or in combination with TRAIL abrogated DARPP-32-induced increase in BCL-xL mRNA level. D) Western blot analysis demonstrated DARPP-32-dependent increase in BCL-xL protein expression that was associated with increased levels of p-Src(Y416) and p-STAT3(Y705) proteins. Treatment with TRAIL in combination with PP1 reversed the pro-survival effect of DARPP-32 as shown by a notable decrease in protein levels of p-Src(Y416), p-STAT3(Y705), and BCL-xL; and evidenced by cleavage of caspase-3.