Proteomic Profiling Identified Multiple Short-lived Members of the Central Proteome as the Direct Targets of the Addicted Oncogenes in Cancer Cells

“Oncogene addiction” is an unexplained phenomenon in the area of cancer targeted therapy. In this study, we have tested a hypothesis that rapid apoptotic response of cancer cells following acute inhibition of the addicted oncogenes is because of loss of multiple short-lived proteins whose activity normally maintain cell survival by blocking caspase activation directly or indirectly. It was shown that rapid apoptotic response or acute apoptosis could be induced in both A431 and MiaPaCa-2 cells, and quick down-regulation of 17 proteins, which were all members of the central proteome of human cells, was found to be associated with the onset of acute apoptosis. Knockdown of PSMD11 could partially promote the occurrence of acute apoptosis in both MiaPaCa-2 and PANC-1 pancreatic cancer cells. These findings indicate that maintaining the stability of central proteome may be a primary mechanism for addicted oncogenes to maintain the survival of cancer cells through various signaling pathways, and quick loss of some of the short-lived members of the central proteome may be the direct reason for the rapid apoptotic response or acute apoptosis following acute inhibition of the addicted oncogenes in cancer cells. These findings we have presented can help us better understand the phenomenon of oncogene-addiction and may have important implications for the targeted therapy of cancer.Although malignant carcinomas frequently contain multiple genetic and epigenetic abnormalities (1–4), their sustained proliferation and/or survival are often dependent on a single activated oncogenic protein or pathway. Acute disruption of the oncogenic activity of the addicted oncoprotein or pathway can cause tumor cells to undergo rapid apoptosis, or sometimes growth arrest and differentiation (5, 6). This phenomenon was first coined as “oncogene addiction” by Bernard Weinstein (5), and now it has been observed in multiple genetically engineered mouse models of human cancers, mechanistic studies in human cancer cell lines, and clinical experience involving specific molecular targeted agents (7), highlighting its potentially important implications of this phenomenon in the treatment of cancer.To explain oncogene addiction, it has been suggested that the rapid apoptotic response observed in tumor cells on acute disruption of an oncogene product results from differential decay rates of various short-lived prosurvival (such as phospho-ERK, -Akt, and -STAT3/5), and longer-lived proapoptotic signals (such as phospho-p38 MAPK) emanating from the oncoprotein (such as EGFR or BCR-ABL) following its inactivation. Although this theory has circumstantial evidence from experimental findings in several systems, the exact molecular mechanism of how these proapoptotic and prosurvival signals were integrated to lead to rapid apoptosis following acute inhibition of the addicted oncogenes is still poorly understood.In recent years, several research groups have documented that inhibition of protein synthesis with cycloheximide alone could also induce rapid apoptosis within 2–4 h in a variety of cancer cell lines (8–12), or could markedly accelerate vinblastine induced apoptosis in several leukemia cell lines with cells dying in 4 h from all phases of the cell cycle, and it has been coined as “acute apoptosis” by Alan Eastman (13) to distinguish it from the delayed apoptosis, which is associated with cell cycle arrest. These research findings suggest that the rapid apoptotic response following acute inhibition of the addicted oncogenes in cancer cells may be caused by loss of multiple short-lived proteins whose activity normally maintains cell survival by blocking caspases activation directly or indirectly. Thus identifying these short-lived proteins can help us better understand the phenomenon of oncogene addiction.In this study we showed that rapid apoptotic response or acute apoptosis could be induced in both A431 cells and pancreatic cancer MiaPaCa-2 cells when treated with corresponding signaling inhibitors, and proteomic profiling identified that the quick down-regulation of 17 short-lived proteins, which were all members of central proteome of human cells, was associated with the onset of acute apoptosis in both A431 and MiaPaCa-2 cells. Knockdown of PSMD11 could partially promote the occurrence of acute apoptosis in both MiaPaCa-2 and PANC-1 pancreatic cancer cells. Based on these and additional findings described below, we conclude that maintaining the stability of central proteome may be a primary mechanism for addicted oncogenes to maintain the survival of cancer cells through various signaling pathways, and quick loss of some of the short-lived members of the central proteome may be the direct reason for the rapid apoptotic response or acute apoptosis following acute inhibition of the addicted oncogenes in cancer cells.