Fig. 6: MDC1 is a target of chemosensitization for irinotecan therapy in colorectal cancer.
a WB of HCT116 cells transfected with indicated siRNA and treated with 100 nM SN-38 for 1 h. b Same as (A), except SN-38 was treated for 24 h to assess c-FLIP expression. Quantification of c-FLIPL levels: n = 3 from three biological replicates, mean ± s.d. ****P < 0.0001, ***P < 0.001, two-way ANOVA. c WB of HCT116 cells transfected with siRNA MDC1#3 and treated with 100 nM SN-38 for indicated times. d Flow cytometry analysis of Annexin V staining in HCT116 cells transfected with indicated siRNA and treated with 100 nM SN-38 for 48 h. n = 3 from three biological replicates, mean ± s.d. **P < 0.01, ns: not significant, two-way ANOVA. e Working model depicting TIPIN’s roles in regulating replication fork dynamics and the DNA damage response. a The TIM-TIPIN complex is required for efficient replication fork progression. TIM acts as a scaffold of the replisome to interact with the CMG helicase while TIPIN stabilizes TIM. b At stalled forks caused by replisome uncoupling (e.g., HU), TIPIN interacts with RPA to recruit CLASPIN and promote ATR-dependent CHK1 phosphorylation. c In response to replication-associated DSBs (e.g., CPT, SN-38), TIPIN amplifies ATM-CHK2 checkpoint signaling, while TIPIN phosphorylation recruits MDC1 to promote ATM-dependent NF-κB signaling that establishes TIS and upregulates c-FLIP, which sustains cell survival by inhibiting caspase-8 activation. Accordingly, targeting MDC1 or potentially its interaction with TIPIN would act as a way to chemosensitize cells in cytotoxic anticancer therapy. Image created with Biorender.com.
