P53 pathway and cancer: From bench to clinic

p53-mediated G1 arrest requires the induction of both p21 and Killin in human colon cancer cells

The main biological function of the tumor suppressor p53 is to control cell cycle arrest and apoptosis. Among the p53 target genes, p21 has been identified as a key player in p53-mediated G1 arrest, while Killin, via its high DNA binding affinity, has been implicated in S and G2/M arrest. However, whether Killin is involved in G1 arrest remains unclear. This research aimed to explore the role of Killin in p53-mediated G1 arrest. Knockout of killin in human colorectal cells led to a dramatic decrease in p53-mediated G1 arrest upon DNA damage. Moreover, double knockout of killin and p21 completely abolished G1 arrest, similar to that of p53 knockout cells. We further showed that Killin could upregulate p21 protein expression independent of p53 via ubiquitination pathways. Immunoprecipitation studies indicated that Killin may directly bind to proteasome subunits, thereby disrupting proteasomal degradation of p21. Together, these results demonstrate that Killin is involved in multiple cell cycle checkpoint controls, including p53-mediated G1 arrest.

Redox-responsive polymer inhibits macrophages uptake for effective intracellular gene delivery and enhanced cancer therapy

The development of advanced gene delivery carriers with stimuli-responsive release manner for tumor therapeutics is desirable, since they can exclusively release the therapeutic gene via their structural changes in response to the specific stimuli of the target site. Moreover, interactions between macrophages and drug delivery systems (DDSs) seriously impair the treatment efficiency of DDSs, thus macrophages uptake inhibition would to some extent improve the intracellular uptake of DDSs in tumor cells. Herein, a PEGylated redox-responsive gene delivery system was developed for effective cancer therapy. PEG modified glycolipid-like polymer (P-CSSO) was electrostatic interacted with p53 to form P-CSSO/p53 complexes, which exhibited an enhanced redox sensitivity in that the disulfide bond was degraded and the rate the plasmid released from P-CSSO was 2.29-fold that of nonresponsive platform (P-CSO-SA) in 10 mM levels of glutathione (GSH). PEGylation could significantly weaken macrophages uptake, while enhance the accumulation of P-CSSO in tumor cells both in vitro and in vivo. Compared with nonresponsive complexes (P-CSO-SA/p53) (59.2%) and Lipofectamine™ 2000/p53 complexes (52.0%), the tumor inhibition rate of P-CSSO/p53 complexes (77.1%) significantly increased, which was higher than CSSO/p53 complexes (69.9%). The present study indicates that tumor microenvironment sensitive and macrophages uptake suppressive P-CSSO/p53 is a powerful in vivo gene delivery system for enhanced anticancer therapy.