CREB1 and melanoma: To further test the relevance of GCP‐2 and ENA‐78 derived from replicative senescent fibroblasts on CREB phosphorylation in vivo, melanoma tumors established after subcutaneous injection of A375 melanoma cells with either non‐senescent or replicative senescent fibroblasts into SCID mice were analyzed for CREBS133 phosphorylation (Figure 4C).