Fig. 5: MC1R signaling through MC1R-cAMP-CREB contributes to the accelerated G1-S transition in breast cancer cells.

a–c. MC1R-KD T-47d cells were synchronized to the G1 phase by a double-thymidine block and then released with or without treatment with 25 μM FSK. (a) Mean ± SEM percentage of cells in the G1, S, and G2 phases at 0, 3, 6, 9, and 12 h post-release. *p < 0.05 (unpaired Student’s t-test). (b) Mean ± SEM percentage of cells in the S phase across time. *p < 0.05 (one-way ANOVA with Dunnett’s multiple comparisons). (c) Representative western blot showing Cyclin D1, Cyclin E1, Ser780 p-Rb, Rb, and GAPDH (loading control). Western blot quantification plots are shown in Supplementary Fig. 4d. d–f. WT T-47d cells were treated with 0.2 μM NDP-MSH or 0.2 μM NDP-MSH + 5 μM 666-15 (CREBi) or left untreated after releasing from a double-thymidine block. (d) Mean ± SEM percentage of cells in the G1, S, and G2 phases at 0, 3, 6, 9, and 12 h post-release. *p < 0.05 (unpaired Student’s t-test). (e) Mean ± SEM percentage of cells in the S phase across time. *p < 0.05 (one-way ANOVA with Dunnett’s multiple comparisons). (f) Representative western blot showing Cyclin D1, Cyclin E1, Ser780 p-Rb, Rb, and GAPDH (loading control). Western blot quantification plots are shown in Supplementary Fig. 4e.