Bcl-2 family members: intracellular targeting, membrane-insertion, and changes in subcellular localization

Abstract

The members of the Bcl-2 family of proteins are crucial regulators of apoptosis. In order to determine cell fate, these proteins must be targeted to distinct intracellular membranes, including the mitochondrial outer membrane (MOM), the membrane of the endoplasmic reticulum (ER) and its associated nuclear envelope. The targeting sequences and mechanisms that mediate the specificity of these proteins for a particular cellular membrane remain poorly defined. Several Bcl-2 family members have been reported to be tail-anchored via their predicted hydrophobic COOH-terminal transmembrane domains (TMDs). Tail-anchoring imposes a posttranslational mechanism of membrane insertion on the already folded protein, suggesting that the transient binding of cytosolic chaperone proteins to the hydrophobic TMD may be an important regulatory event in the targeting process. The TMD of certain family members is initially concealed and only becomes available for targeting and membrane insertion in response to apoptotic stimuli. These proteins either undergo a conformational change, posttranslational modification or a combination of these events enabling them to translocate to sites at which they are functional. Some Bcl-2 family members lack a TMD, but nevertheless localize to the MOM or the ER membrane during apoptosis where they execute their functions. In this review, we will focus on the intracellular targeting of Bcl-2 family members and the mechanisms by which they translocate to their sites of action. Furthermore, we will discuss the posttranslational modifications which regulate these events.

Bcl-2 proteins link programmed cell death with growth and morphogenetic adaptations in the fungal plant pathogen Colletotrichum gloeosporioides

“…In addition, similar GFP distribution pattern was also observed in isolates expressing GFP fused to a mitochondria localizing sequence (data not shown). These results suggest that the Bcl-2 protein is localized in C. gloeosporioides mitochondria, as well as in other cellular compartments such as ER, similar to its localization in mammalian cells (Schinzel et al, 2004).…”

Impact of pH on Bax α conformation, oligomerisation and mitochondrial integration

“…Thus, the absence of Bax in the second filtration (i.e., MicroCon YM‐50) means that all the Bax was present as a monomer. (B) IVT Bax or Bax K64E [1], incubated at two pH (i.e., pH 7.4 and 8.2), filtered through MicroCon YM‐30 [2] and MicroCon YM‐50 [3]. Since 35 S‐Met‐Bax (Bax) or Bax K64E was eluted in a large volume (about 500 μl), Bax was immunoprecipitated, as described in Section 2, with the 2D2 antibody (IP‐Bax) or with non‐immune IgG, as a control for non‐specific IP (IP‐IgG).…”

“…Members of the Bcl‐2 family are the final regulators of apoptosis, one of the major cell death programmes, induced by a variety of physiological situations and death inducers [1]. The pro‐apoptotic protein Bax α (Bax) is normally contained in an inactive conformation in healthy cells and its activation during the early phases of apoptosis is associated with changes in the conformation [2]. These changes involve not only the unblocking of the addressing signal of Bax and the insertion into the mitochondrial outer membrane, but also the subsequent oligomerisation step [3].…”

Intestinal mucositis: the role of the Bcl-2 family, p53 and caspases in chemotherapy-induced damage

“…The mitochondria play a crucial role in the activation of apoptosis, with growing evidence that all Bcl-2 family members described so far act exclusively on the cytoplasmic face of the mitochondria (and/or the endoplasmic reticulum) [169]. Apoptotic stimuli have been shown to initiate a change in mitochondrial membrane potential prior to caspase-dependent cell death.…”

“…Furthermore, removing the C-terminus from the proteins halted membrane insertion but did not alter their death-promoting or death-inhibiting action [69]. Although little data are published, proteins that may be involved in binding the Bcl-2 family to the mitochondria or putative membrane receptors include the TOM-proteins (TOM-20 and 22) and mitochondrial FK506-binding protein 38 [169].…”