The promotion of tumor development by Dickkopf 4 (DKK4) is receiving increased attention. However, the association between DKK4 and pancreatic cancer remains unclear. DKK4 expression was measured in pancreatic ductal adenocarcinoma tissues using qRT-PCR and immunohistochemistry. A DKK4-overexpressing pancreatic cancer cell line was established, and the differentially expressed genes (DEGs) that were induced by DKK4 were identified using transcriptome sequencing. The association between the identified DEGs and pancreatic cancer was assessed using gene ontology (GO), pathway analysis, pathway interaction networks, differentially expressed gene interaction network analysis, and co-expression gene networks. Finally, the accuracy of the analyses was validated using serial paraffin and frozen sections of clinical samples. DKK4 is highly expressed in pancreatic cancer tissues. DEGs of overexpression DKK4 of PANC-1 are mostly upregulated. GO and pathway analysis showed that DKK4 are associated with tumor and organ development and immune inflammation. The mitogen-activated protein kinase (MAPK) signaling pathway was the main signal transduction pathway that showed significant enrichment in overexpression DKK4 of PANC-1. The results of GO, pathway analyses, and differentially expressed gene interaction network identified genes that are closely associated with tumor development, including MAPK3, PIK3R3, VAV3, JAG1, and Notch3. The immunohistochemistry and immunofluorescence results suggested that DKK4 is co-expressed with MAPK3 and VAV3 in pancreatic cancer tissues. The results presented here show for the first time that DKK4 is highly expressed in pancreatic cancer tissues. Bioinformatics analysis of a DKK4-overexpressing of PANC-1 identified several oncogenes that are closely associated with tumors, and the MAPK signaling pathway is the core signal transduction pathway. DKK4 can be co-expressed with MAPK3 and VAV3 in pancreatic ductal adenocarcinoma tissues. Thus, DKK4 may have function on the development and progression of pancreatic cancer.
Pro-apoptotic multi-domain proteins of the BCL2 family such as BAX and BAK are well known for their important role in the induction of mitochondrial outer membrane permeabilization (MOMP), which is the rate-limiting step of the intrinsic pathway of apoptosis. Human or mouse cells lacking both BAX and BAK (due to a double knockout, DKO) are notoriously resistant to MOMP and cell death induction. Here we report the surprising finding that BAX/BAK DKO cells proliferate less than control cells expressing both BAX and BAK (or either BAX or BAK) when they are driven into tetraploidy by transient exposure to the microtubule inhibitor nocodazole. Mechanistically, in contrast to their BAX/BAK-sufficient controls, tetraploid DKO cells activate a senescent program, as indicated by the overexpression of several cyclin-dependent kinase inhibitors and the activation of β-galactosidase. Moreover, DKO cells manifest alterations in ionomycin-mobilizable endoplasmic reticulum (ER) Ca2+ stores and store-operated Ca2+ entry that are affected by tetraploidization. DKO cells manifested reduced expression of endogenous sarcoplasmic/endoplasmic reticulum Ca2+ ATPase 2a (Serca2a) and transfection-enforced reintroduction of Serca2a, or reintroduction of an ER-targeted variant of BAK into DKO cells reestablished the same pattern of Ca2+ fluxes as observed in BAX/BAK-sufficient control cells. Serca2a reexpression and ER-targeted BAK also abolished the tetraploidy-induced senescence of DKO cells, placing ER Ca2+ fluxes downstream of the regulation of senescence by BAX/BAK. In conclusion, it appears that BAX/BAK prevent the induction of a tetraploidization-associated senescence program. Speculatively, this may contribute to the low incidence of cancers in BAX/BAK DKO mice and explain why human cancers rarely lose the expression of both BAX and BAK.
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