Objective: To investigate the changes of ID1 expression in tumor cells treated with etoposide, cisplatin and ultraviolet (UV) irradiation, and explore the effect of ID1 on chemotherapeutic drug- and UV-induced apoptosis.
Methods: In the present study, upon onset of apoptosis induced by various kinds of inducers such as etoposide, cisplatin and UV irradiation, the expression level of ID1 was detected by Western blot and real-time PCR. We also analyzed the half-life of ID1 protein and stability of ID1 mRNA respectively by cycloheximide inhibition test and RT-PCR. Annexin-V assay was carried out to evaluate the contribution of ID1 protein to chemotherapeutic drug- and UV-induced apoptosis.
Results: ID1 expression presented a profound down-regulation in the HCT116 cells treated with etoposide, cisplatin and UV irradiation(P<0.05 for all). The apoptosis in the UV irradiation group, cisplatin group, etoposide group was (58.70±1.55)%, (35.80±0.92)% and (21.00±0.72)%, respectively, significantly higher than that of the control group(1.10±0.07)%, (1.20±0.13)% and (3.50±0.23)% (P<0.05 for all). Upon etoposide treatment, ID1 expression level was decreased via induction of mRNA instability, but not the protein degradation changes. Additionally, ectopic expression of ID1 in the HCT116 cells alleviated etoposide-, cisplatin- and UV-induced apoptosis. The results of flow eytometry revealed that the percentage of apoptotic cells in the ID1 group under the treatment of etoposide, cisplatin and UV irradiation was (23.80±0.82)%, (17.80±1.34)% and (13.40±0.53)%, respectively, significantly lower than that in the empty vector group (41.10±1.61)%, (30.40±2.67)% and (22.50±3.47)% (P<0.05 for all).
Conclusions: These observations indicate that the treatment with etoposide reduces the amount of ID1 by induction of mRNA instability, and exogenously introduced ID1 protects cells against etoposide-, cisplatin- and UV irradiation-induced apoptosis. Inhibition of the ID1 bioactivity may become a new strategy in cancer treatment.