MUC1-C induces MYC expression. (A-B) RPMI8226 (A) and U266 (B) cells were silenced for MUC1 using CRISPR/Cas9. The parental WT and CRISPR cells were analyzed for MYC mRNA levels by qRT-PCR (left). The results (mean ± standard deviation [SD] of 3 determinations) are expressed as relative MYC mRNA levels as compared with that obtained for the WT cells (assigned a value of 1). Forward and reverse primers are listed in supplemental Table 1. Lysates from the WT and CRISPR cells were immunoblotted with the indicated antibodies (right). (C) Schema of the MUC1-C subunit with the 58-aa extracellular domain (ED), the 28-aa transmembrane domain (TM), and the 72-aa cytoplasmic domain (CD). The CD sequence is highlighted at the CQC motif, which is necessary and sufficient for MUC1-C homodimerization, and is targeted by GO-203 and not the control peptide CP-2. Also, highlighted are (1) the site for GSK3β phosphorylation and (2) the region for direct β-catenin binding. (D-E) RPMI8226 (D) and U266 (E) cells were treated with 5 μM CP-2 or GO-203 for 48 hours. The cells were analyzed for MYC mRNA levels by qRT-PCR (left). The results (mean ± SD of 3 determinations) are expressed as relative MYC mRNA levels as compared with that obtained for the CP-2–treated cells (assigned a value of 1). Lysates from the CP-2– and GO-203–treated cells were immunoblotted with the indicated antibodies (right). EGFR, epidermal growth factor receptor; IB, immunoblot; SRC, Src protooncogene, nonreceptor tyrosine kinase.