Bcl-2 is an integral component of mitotic chromosomes

Nucleolar protein TAAP1/C22orf46 confers pro-survival signaling in non-small cell lung cancer

Tumor cells subvert immune surveillance or lytic stress by harnessing inhibitory signals. Hence, bispecific antibodies have been developed to direct CTLs to the tumor site and foster immune-dependent cytotoxicity. Although applied with success, T cell-based immunotherapies are not universally effective partially because of the expression of pro-survival factors by tumor cells protecting them from apoptosis. Here, we report a CRISPR/Cas9 screen in human non-small cell lung cancer cells designed to identify genes that confer tumors with the ability to evade the cytotoxic effects of CD8+ T lymphocytes engaged by bispecific antibodies. We show that the gene C22orf46 facilitates pro-survival signals and that tumor cells devoid of C22orf46 expression exhibit increased susceptibility to T cell-induced apoptosis and stress by genotoxic agents. Although annotated as a non-coding gene, we demonstrate that C22orf46 encodes a nucleolar protein, hereafter referred to as "Tumor Apoptosis Associated Protein 1," up-regulated in lung cancer, which displays remote homologies to the BH domain containing Bcl-2 family of apoptosis regulators. Collectively, the findings establish TAAP1/C22orf46 as a pro-survival oncogene with implications to therapy.

Subcellular Localization and Dynamics of the Bcl-2 Family of Proteins

Bcl-2 family proteins are recognized as major regulators of the mitochondrial pathway of apoptosis. They control the mitochondrial outer membrane permeabilization (MOMP) by directly localizing to this organelle. Further investigations demonstrated that Bcl-2 related proteins are also found in other intracellular compartments such as the endoplasmic reticulum, the Golgi apparatus, the nucleus and the peroxisomes. At the level of these organelles, Bcl-2 family proteins not only regulate MOMP in a remote fashion but also participate in major cellular processes including calcium homeostasis, cell cycle control and cell migration. With the advances of live cell imaging techniques and the generation of fluorescent recombinant proteins, it became clear that the distribution of Bcl-2 proteins inside the cell is a dynamic process which is profoundly affected by changes in the cellular microenvironment. Here, we describe the current knowledge related to the subcellular distribution of the Bcl-2 family of proteins and further emphasize on the emerging concept that this highly dynamic process is critical for cell fate determination.

Nuclear glutathione

Glutathione (GSH) is a linchpin of cellular defences in plants and animals with physiologically-important roles in the protection of cells from biotic and abiotic stresses. Moreover, glutathione participates in numerous metabolic and cell signalling processes including protein synthesis and amino acid transport, DNA repair and the control of cell division and cell suicide programmes. While it is has long been appreciated that cellular glutathione homeostasis is regulated by factors such as synthesis, degradation, transport, and redox turnover, relatively little attention has been paid to the influence of the intracellular partitioning on glutathione and its implications for the regulation of cell functions and signalling. We focus here on the functions of glutathione in the nucleus, particularly in relation to physiological processes such as the cell cycle and cell death. The sequestration of GSH in the nucleus of proliferating animal and plant cells suggests that common redox mechanisms exist for DNA regulation in G1 and mitosis in all eukaryotes. We propose that glutathione acts as "redox sensor" at the onset of DNA synthesis with roles in maintaining the nuclear architecture by providing the appropriate redox environment for the DNA replication and safeguarding DNA integrity. In addition, nuclear GSH may be involved in epigenetic phenomena and in the control of nuclear protein degradation by nuclear proteasome. Moreover, by increasing the nuclear GSH pool and reducing disulfide bonds on nuclear proteins at the onset of cell proliferation, an appropriate redox environment is generated for the stimulation of chromatin decompaction. This article is part of a Special Issue entitled Cellular functions of glutathione.

Clinical implication and mitotic effect of CD44 cleavage in relation to osteopontin/CD44 interaction and dysregulated cell cycle protein in gastrointestinal stromal tumor

BACKGROUND

CD44 and osteopontin (OPN) are functionally related molecules that, alone or in combination, play miscellaneous biological and pathophysiologic roles. CD44 cleavage, one unique feature of CD44, occurs in human cancers, but its function remains unclear. This study aimed to assess the clinicopathologic significance and mechanism of CD44 cleavage in gastrointestinal stromal tumor (GIST) with respect to OPN and OPN/CD44 interaction.

MATERIALS AND METHODS

CD44 cleavage was evaluated by immunoblotting in 31 primary GIST tumor specimens with paired normal tissues. OPN/CD44 interaction was examined by in situ proximity ligation assay. The associations of CD44 cleavage activity with clinicopathologic parameters, cyclin D1 expression, beta-catenin expression, OPN expression, and OPN/CD44 interaction were analyzed.

RESULTS

CD44 cleavage activity was demonstrated in 87.1% of GIST, in contrast to its absence in normal tissues. Increased CD44 cleavage activity was significantly associated with enhanced mitosis by multivariate analysis, in addition to being related to tumor size, recurrence, high-risk status, and poor survival by univariate analysis. Mitosis was significantly higher in GIST with increased CD44 cleavage activity, which also positively correlated with tumor-specific beta-catenin and cyclin D1 overexpression, indicating a mitotic effect through aberrant cell cycle. Both OPN and OPN/CD44 interactions were significantly associated with CD44 cleavage.

CONCLUSION

Our study demonstrates the clinicopathological significance of CD44 cleavage in GIST. There is a significantly increased mitosis associated with CD44 cleavage in relation to OPN/CD44 interaction and dysregulated cell cycle in GIST.

Differential protection by wildtype vs. organelle-specific Bcl-2 suggests a combined requirement of both the ER and mitochondria in ceramide-mediated caspase-independent programmed cell death

Background

Programmed cell death (PCD) is essential for development and homeostasis of multicellular organisms and can occur by caspase-dependent apoptosis or alternatively, by caspase-independent PCD (ciPCD). Bcl-2, a central regulator of apoptosis, localizes to both mitochondria and the endoplasmic reticulum (ER). Whereas a function of mitochondrial and ER-specific Bcl-2 in apoptosis has been established in multiple studies, corresponding data for ciPCD do not exist.

Methods

We utilized Bcl-2 constructs specifically localizing to mitochondria (Bcl-2 ActA), the ER (Bcl-2 cb5), both (Bcl-2 WT) or the cytosol/nucleus (Bcl-2 ΔTM) and determined their protective effect on ceramide-mediated ciPCD in transiently and stably transfected Jurkat cells. Expression of the constructs was verified by immunoblots. Ceramide-mediated ciPCD was induced by treatment with human recombinant tumor necrosis factor and determined by flow cytometric measurement of propidium iodide uptake as well as by optical analysis of cell morphology.

Results

Only wildtype Bcl-2 had the ability to efficiently protect from ceramide-mediated ciPCD, whereas expression of Bcl-2 solely at mitochondria, the ER, or the cytosol/nucleus did not prevent ceramide-mediated ciPCD.

Conclusion

Our data suggest a combined requirement for both mitochondria and the ER in the induction and the signaling pathways of ciPCD mediated by ceramide.