Anti-cell death activity promotes pulmonary metastasis of melanoma cells

Abstract

Bcl-2 inhibits apoptosis from a variety of stimuli, and a Bcl-2-binding protein BAG-1 also functions in protection from apoptosis in concert with Bcl-2. Here, we provide evidence that prolonged cell survival introduced by overexpression of Bcl-2 or BAG-1 proteins strongly promotes experimental pulmonary metastasis of melanoma B16-BL6 cells. In murine melanoma cell line B16-BL6, gene transfer-mediated expression of the Bcl-2 or BAG-1 led to prolonged cell survival against serumstarved apoptosis in vitro. The Bcl-2-expressing B16 cells, B16-Bcl-2 and the BAG-1-expressing B16 cells, B16-BAG-1 strongly enhanced pulmonary metastasis in allogenic BALB/c nude mice and whole lung weights were increased by 2.4-fold and 1.4-fold, respectively, compared with control transfectants, suggesting that Bcl-2 is a stronger positive modulator of metastasis. When the viable B16-Bcl-2 and control transfectants were injected subcutaneously into BALB/c nude mice, the colony numbers of pulmonary metastasis of the B16-Bcl-2 transfectant increased by 5.6-fold compared with the control transfectants. These enhanced metastatic potentials in the B16-Bcl-2 and the B16-BAG-1 transfectants were well correlated with anti-cell death activity against serum-starvation and enhanced cell viability on limiting dilution. Analysis of the transfectants however revealed that their growth rates, invasive ability and cell motility were not signi®cantly altered by overexpression of either Bcl-2 or BAG-1 proteins. Taken together, these studies demonstrate that prolonged cell survival is a crucial factor to promote metastasis of melanoma, thereby contributing to tumor progression.

BAG-1 accelerates cell motility of human gastric cancer cells

“…To examine the potential role of BAG-1 in promoting cell migration, the MKN74 transfectants were analysed by goldparticle colloid assay with or without FBS or HGF as described previously (Takaoka et al, 1997). The MKN74-BAG-1 transfectants exhibited increased migration (approximately 2 ± 3-fold increase) as compared with the MKN74-NEO transfectants and parental MKN74 cells (Figure 2).…”

“…In transfection experiments, overexpression of BAG-1 can prolong cell survival alone or in combination with Bcl-2 overexpression. Murine melanoma B16-BL6 transfectant cells overexpressing BAG-1 have been shown to be resistant to apoptosis and exhibited enhanced pulmonary metastasis (Takaoka et al, 1997). Overexpression of BAG-1 in a human gastric cancer cell line led to prolonged cell survival against apoptosis induced by cell detachment`anoikis' and increased peritoneal dissemination in animals, which were attributed to its ability to promote cell survival in a detached state (Yawata et al, 1998).…”

Hypoxia selects for high-metastatic Lewis lung carcinoma cells overexpressing Mcl-1 and exhibiting reduced apoptotic potential in solid tumors

“…There is accumulating evidence that developing resistance to common apoptotic stimuli is one of the factors that confer high metastatic capability to tumor cells (Glinsky and Glinsky, 1996;McConkey et al, 1996;Bufalo et al, 1997;Glinsky, 1997;Inbal et al, 1997;Shtivelman, 1997;Takaoka et al, 1997;Fernandez et al, 2000;Lowe and Lin, 2000;Wong et al, 2001). The apoptosis-resistant phenotype may be advantageous for tumor cells to survive in the metastatic process.…”

BAG-1 expression and function in human cancer

“…Heat shock proteins are also required for cell survival and direct activation of these functions may also be important. Suppression of apoptosis might contribute to the ability of BAG-1 to promote metastatic spread (Takaoka et al, 1997;Yawata et al, 1998). Alternatively, increased metastasis may be mediated by enhanced cell motility (Yawata et al, 1998).…”

“…BAG-1 enhances metastasis in experimental models (Takaoka et al, 1997;Yawata et al, 1998) and Shindoh et al (2000) demonstrated that BAG-1 was expressed in 89% of primary tumours with nodal metastasis compared to 38% of tumours without. BAG-1 expression levels were determined by densitometry and although this alleviates the subjectivity of scoring BAG-1 labelling intensity to some extent it does not give information on whether the immunoreactivity is nuclear or cytoplasmic.…”