(a) Tumorsphere cultures of MECs expressing NICD/shLuc or NICD/shPar3 in the presence or absence of 25μM JNK inhibitor (SP600125, Sigma). (b) Quantification of tumorsphere sizes from (a), n=3. (c and d) Immunoblots of NICD/shLuc and NICD/shPar3 tumorsphere lysates (c) or co-expressing dominant negative HA-Rac1T17N (d). Antibodies used were rabbit anti-Par3 (Macara lab12), mouse anti-Myc (1:1000, McGill hybridoma facility), rabbit anti-HA (1:1000, McGill hybridoma facility), rabbit anti-pJNK (pThr183/Tyr185, 1:1000, Cell Signaling Technology), mouse anti-a-tubulin as a loading control (1:5000, Sigma). (e) NICD/shLuc and NICD/shPar3 mammary tumor sections were stained for phospho-JNK (1:100). (f) Quantification of cells with nuclear phospho-JNK from (e). Two regions from each of 3 tumors were analyzed for each. p-values were calculated using the ANOVA with Tukey HSD post-hoc test (b) or student’s t-test (f). Error bars represent sd (e) or sem (f). Scale bars = 1mm (a) and 20μm (e).