C/EBPß suppresses keratinocyte autonomous type 1 IFN response and p53 to increase cell survival and susceptibility to UVB-induced skin cancer.

p53 is activated by DNA damage and oncogenic stimuli to regulate senescence, apoptosis and cell-cycle arrest, which are essential to prevent cancer. Here, we utilized UVB radiation, a potent inducer of DNA damage, p53, apoptosis and skin cancer to investigate the mechanism of CCAAT/enhancer binding protein-ß (C/EBPß) in regulating p53-mediated apoptosis in keratinocytes and to test whether the deletion of C/EBPß in epidermis can protect mice from UVB-induced skin cancer. UVB-treatment of C/EBPß skin conditional knockout (CKOß) mice increased p53 protein levels in epidermis and enhanced p53-dependent apoptotic activity 3-fold compared with UVB-treated control mice. UVB increased C/EBPß levels through a p53-dependent pathway and stimulated the formation of a C/EBPß-p53 protein complex; knockdown of C/EBPß increased p53 protein stability in keratinocytes. These results suggest a p53-C/EBPß feedback loop, whereby C/EBPß, a transcriptional target of a p53 pathway, functions as a survival factor by negatively regulating p53 apoptotic activity in response to DNA damage. RNAseq analysis of UVB-treated CKOß epidermis unexpectedly revealed that type 1 interferon (IFN) pathway was the most highly enriched pathway. Numerous pro-apoptotic interferon stimulated genes were upregulated including some known to enhance p53 apoptosis. Our results indicate that p53 and IFN pathways function together in response to DNA damage to result in the activation of extrinsic apoptosis pathways and caspase 8 cleavage. Last, we observed CKOß mice were resistant to UVB-induced skin cancer. Our results suggest that C/EBPß represses apoptosis through keratinocyte autonomous suppression of the type 1 IFN response and p53 to increase cell survival and susceptibility to UVB-induced skin cancer.

A cost-effective device for the rapid transfer of gel-separated proteins onto membranes.

We describe here the fabrication of a cost-effective semi-dry blotting apparatus for the transfer of proteins onto membranes. Graphite sheets were used as electrodes. Protein mixtures were separated on NuPAGE 4% to 12% polyacrylamide gradient gels. With a Tris-bicine buffer, we demonstrated that close to 80% of the proteins with apparent molecular mass of 80kDa or less were removed from the gels after 8min of blotting. The process is much faster than the techniques reported previously in the literature.

C/EBPß deletion in oncogenic Ras skin tumors is a synthetic lethal event.

Therapeutic targeting of specific genetic changes in cancer has proven to be an effective therapy and the concept of synthetic lethality has emerged. CCAAT/enhancer-binding protein-ß (C/EBPß), a basic leucine zipper transcription factor, has important roles in cellular processes including differentiation, inflammation, survival, and energy metabolism. Using a genetically engineered mouse model, we report that the deletion C/EBPß in pre-existing oncogenic Ha-Ras mouse skin tumors in vivo resulted in rapid tumor regression. Regressing tumors exhibited elevated levels of apoptosis and p53 protein/activity, while adjacent C/EBPß-deleted skin did not. These results indicate that the deletion of C/EBPß de-represses p53 in oncogenic Ras tumors but not in normal wild-type Ras keratinocytes, and that C/EBPß is essential for survival of oncogenic Ras tumors. Co-deletion of C/EBPß and p53 in oncogenic Ras tumors showed p53 is required for tumor regression and elevated apoptosis. In tumors, loss of a pathway that confers adaptability to a stress phenotype of cancer/tumorigenesis, such as DNA damage, could result in selective tumor cell killing. Our results show that oncogenic Ras tumors display a significant DNA damage/replicative stress phenotype and these tumors have acquired a dependence on C/EBPß for their survival. RNAseq data analysis of regressing tumors deleted of C/EBPß indicates a novel interface between p53, type-1 interferon response, and death receptor pathways, which function in concert to produce activation of extrinsic apoptosis pathways. In summary, the deletion of C/EBPß in oncogenic Ras skin tumors is a synthetic lethal event, making it a promising target for future potential anticancer therapies.