The ever-lengthening arm of p53

Evaluation of Coupled Nuclear and Cytoplasmic p53 Dynamics

The tumor suppressor protein p53 predominantly serves as a sequence specific transcription factor that may be activated upon exposure to diverse stimuli. One potent death inducer, p53-upregulated mediator of apoptosis (PUMA), is transcriptionally induced by p53. Once released into the cytoplasm, PUMA can lead to the activation of Bcl-2 apoptotic network. The cytoplasmic proapoptotic roles of p53 have recently been discovered, and these findings have placed p53 into the chemical interaction network with Bcl-2 family members. PUMA can also relieve p53 from the sequestration of antiapoptotic members. Released p53 further enters the nucleus and induces PUMA expression. We proposed that this positive feedback loop could lead to bistability. Further sensitivity analysis suggested that the system which covers the interactions between p53 and BCL-2 family members is considerably sensitive to p53 production rate. Meanwhile, downstream network components are much more affected by certain parameters than upstream effectors. Therefore, this newly discovered positive feedback loop might play critical roles in apoptotic network.

Simvastatin prevents skeletal metastasis of breast cancer by an antagonistic interplay between p53 and CD44

Substantial data from clinical trials and epidemiological studies show promising results for use of statins in many cancers, including mammary carcinoma. Breast tumor primarily metastasizes to bone to form osteolytic lesions, causing severe pain and pathological fracture. Here, we report that simvastatin acts as an inhibitor of osteolysis in a mouse model of breast cancer skeletal metastasis of human mammary cancer cell MDA-MB-231, which expresses the mutant p53R280K. Simvastatin and lovastatin attenuated migration and invasion of MDA-MB-231 and BT-20 breast tumor cells in culture. Acquisition of phenotype to express the cancer stem cell marker, CD44, leads to invasive potential of the tumor cells. Interestingly, statins significantly decreased the expression of CD44 protein via a transcriptional mechanism. shRNA-mediated down-regulation of CD44 markedly reduced the migration and invasion of breast cancer cells in culture. We identified that in the MDA-MB-231 cells, simvastatin elevated the levels of mutated p53R280K, which was remarkably active as a transcription factor. shRNA-derived inhibition of mutant p53R280K augmented the expression of CD44, leading to increased migration and invasion. Finally, we demonstrate an inverse correlation between expression of p53 and CD44 in the tumors of mice that received simvastatin. Our results reveal a unique function of statins, which foster enhanced expression of mutant p53R280K to prevent breast cancer cell metastasis to bone.

Tumour-initiating cells: challenges and opportunities for anticancer drug discovery

The hypothesis that cancer is driven by tumour-initiating cells (popularly known as cancer stem cells) has recently attracted a great deal of attention, owing to the promise of a novel cellular target for the treatment of haematopoietic and solid malignancies. Furthermore, it seems that tumour-initiating cells might be resistant to many conventional cancer therapies, which might explain the limitations of these agents in curing human malignancies. Although much work is still needed to identify and characterize tumour-initiating cells, efforts are now being directed towards identifying therapeutic strategies that could target these cells. This Review considers recent advances in the cancer stem cell field, focusing on the challenges and opportunities for anticancer drug discovery.