The RBL-2H3 cell line is a commonly used histamine-releasing cell line used in inflammation, allergy and immunological research. Quite commonly, it is referred to in research papers as a mast cell line, despite the fact that it is derived from basophils. There is also a lack of consistency, both between different research groups using the same cell line and with both mast cell and basophil physiology. The review follows the development of the RBL-2H3 cell line from its inception and then goes on to assess the nature of the cell line in terms of its characteristics and its response to various stimuli. The relationship of this cell line to the various mast cell subtypes and basophils is discussed and it is concluded that while the RBL-2H3 cell line shares some characteristics with both mast cells and basophils, it is not fully representative of either.

Anti-apoptotic Bcl-2 family proteins are often highly expressed in chemotherapy-resistant cancers and impair mitochondrial outer membrane permeabilisation (MOMP), a key requirement for caspase activation via the intrinsic apoptosis pathway. Interestingly, while Bcl-2 overexpression in HeLa cervical cancer cells abrogated caspase processing in response to intrinsic apoptosis induction by staurosporine, tunicamycin or etoposide, residual caspase processing was observed following proteasome inhibition by bortezomib, epoxomicin or MG-132. Similar responses were found in Bcl-2 overexpressing H460 NSCLC cells and Bax/Bak-deficient mouse embyronic fibroblasts. Mild caspase processing resulted in low DEVDase activities, which were MOMP independent and persisted for long periods without evoking immediate cell death. Surprisingly, depletion of caspase-3 and experiments in caspase-7-depleted MCF-7-Bcl-2 cells indicated that the DEVDase activity did not originate from effector caspases. Instead, FADD-dependent caspase-8 activation was the major contributor to the slow, incomplete substrate cleavage. Casapse-8 activation was independent of death ligands but required the induction of autophagy and the presence of Atg5. Depletion of XIAP or addition of XIAP-antagonizing peptides resulted in a switch towards efficient apoptosis execution, suggesting that the requirement for MOMP was bypassed by activating the caspase-8/caspase-3 axis. Combination treatments of proteasome inhibitors and XIAP antagonists therefore represent a promising strategy to eliminate highly resistant cancer cells which overexpress anti-apoptotic Bcl-2 family members.

While RBL-2H3 cells may be useful as a model for mast cell IgE-mediated degranulation, other aspects may not be representative and they may share similarities with basophils rather than with other histamine-releasing cell types.

Many cancer entities and their associated cell line models are highly heterogeneous in their responsiveness to apoptosis inducers and, despite a detailed understanding of the underlying signaling networks, cell death susceptibility currently cannot be predicted reliably from protein expression profiles. Here, we demonstrate that an integration of quantitative apoptosis protein expression data with pathway knowledge can predict the cell death responsiveness of melanoma cell lines. By a total of 612 measurements, we determined the absolute expression (nM) of 17 core apoptosis regulators in a panel of 11 melanoma cell lines, and enriched these data with systems-level information on apoptosis pathway topology. By applying multivariate statistical analysis and multi-dimensional pattern recognition algorithms, the responsiveness of individual cell lines to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or dacarbazine (DTIC) could be predicted with very high accuracy (91 and 82% correct predictions), and the most effective treatment option for individual cell lines could be pre-determined in silico. In contrast, cell death responsiveness was poorly predicted when not taking knowledge on protein-protein interactions into account (55 and 36% correct predictions). We also generated mathematical predictions on whether anti-apoptotic Bcl-2 family members or x-linked inhibitor of apoptosis protein (XIAP) can be targeted to enhance TRAIL responsiveness in individual cell lines. Subsequent experiments, making use of pharmacological Bcl-2/Bcl-xL inhibition or siRNA-based XIAP depletion, confirmed the accuracy of these predictions. We therefore demonstrate that cell death responsiveness to TRAIL or DTIC can be predicted reliably in a large number of melanoma cell lines when investigating expression patterns of apoptosis regulators in the context of their network-level interplay. The capacity to predict responsiveness at the cellular level may contribute to personalizing anti-cancer treatments in the future.

The regulation of apoptotic cell death, a terminal and fatal cell fate decision, has been intensely investigated and, due to its paramount implications for human health and disease, has sparked one of the most prolific and competitive research fields in biological and biomedical sciences of the past decades. Many key components of the molecular machinery processing and transducing apoptotic cell death signals have been described in great detail by now, dramatically advancing our understanding of how the network of apoptosis signaling proteins integrates and regulates cell death signals, and ultimately executes apoptosis. Building on the latest significant advances in deciphering apoptosis signal transduction as well as on the central original groundbreaking discoveries in cell death research, we here present an in-depth description of the current knowledge on the core molecular machinery of apoptotic signaling and how it is implicated in human physiology and pathophysiologies.