Mcl-1 Expression in Human Neutrophils: Regulation by Cytokines and Correlation With Cell Survival

Abstract

Human neutrophils possess a very short half-life because they constitutively undergo apoptosis. Cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), and other agents can rescue neutrophils from apoptosis but the molecular mechanisms involved in this rescue are undefined. Here, we show by Western blotting that human neutrophils do not express Bcl-2 or Bcl-X but constitutively express Bax. However, cellular levels of these proteins are unaffected by agents which either accelerate or delay neutrophil apoptosis. In contrast, neutrophils express the antiapoptotic protein Mcl-1 and levels of this protein correlate with neutrophil survival. Thus, cellular levels of Mcl-1 decline as neutrophils undergo apoptosis and are enhanced by agents (eg, GM-CSF, interleukin-1β, sodium butyrate, and lipopolysaccharide) that promote neutrophil survival. Neutrophils only possess few, small mitochondria, and much of the Mcl-1 protein seems to be located in nuclear fractions. These observations provide the first evidence implicating a Bcl-2 family member in the regulation of neutrophil survival. Moreover, this work also provides a potential mechanism whereby cytokine-regulated gene expression regulates the functional lifespan of neutrophils and hence their ability to function for extended time periods during acute inflammation.

Virus-Infected Alveolar Epithelial Cells Direct Neutrophil Chemotaxis and Inhibit Their Apoptosis

“…Spontaneous PMN apoptosis has been shown to be a caspasedependent apoptotic program because PMNs incubated with caspase inhibitors do not undergo apoptosis and can be triggered by extrinsic and intrinsic apoptotic pathways (47). There are several studies that associate spontaneous PMN apoptosis with intrinsic mitochondrial signaling, including a decline in antiapoptotic protein Mcl-1, translocation of proapoptotic Bax to the mitochondrium, and subsequent release of cytochrome c and caspase 9 activation (48,49). Other studies have described caspase 8-dependent spontaneous PMN apoptosis, involving ligand-independent clustering of death receptors (24).…”

Helicobacter pylori-derived neutrophil-activating protein increases the lifespan of monocytes and neutrophils

“…It has been demonstrated that an improvement of monocyte survival can be achieved by the addition of pro-inflammatory cytokines such as tumour necrosis factoralpha (TNF-a), IL-1b and GM-CSF (Mangan and Wahl, 1991;Moulding et al, 1998;Flad et al, 1999). In a previous report, we demonstrated that HP-NAP stimulates monocytes to secrete TNF-a (Amedei et al, 2006) but the possibility that also IL-1b and GM-CSF could be induced has not been yet investigated.…”

Characterisation of Mcl‐1 cleavage during apoptosis of haematopoietic cells

“…It also has a C-terminal hydrophobic domain that is responsible for the localization of Mcl-1 to membranes within the cell, in particular to the mitochondrial membrane (Yang et al, 1996;Akgul et al, 2000). While it appears that Mcl-1 may not be as potent a protector against apoptosis as Bcl-2 (Reynolds et al, 1996), it does appear to be the main anti-apoptotic protein in some cell types including neutrophils (Moulding et al, 1998). Unlike other Bcl-2 family members, Mcl-1 contains a large region consisting of two PEST sequences that have been thought to target Mcl-1 for rapid degradation within the cell.…”

“…The expression of Mcl-1 can be regulated at a transcriptional as well as a post-translational level. Its expression is increased in response to signalling from a number of different cytokines (Chao et al, 1998;Moulding et al, 1998;Huang et al, 2000;Puthier et al, 2001;Pelletier et al, 2002;Tumang et al, 2002). A recent study shows that Mcl-1 is rapidly degraded by the proteasome during induction of apoptosis by UV irradiation in Hela cells (Nijhawan et al, 2003).…”