Protection of mammalian cells from the toxicity of bleomycin by expression of a bleomycin-binding protein gene from Streptomyces verticillus.

A gene, blmA, encodes a bleomycin (Bm)-binding protein, designated BLMA, from Bm-producing Streptomyces verticillus and confers resistance to Bm in Streptomyces and Escherichia coli cells. In the present study, by transfection of the gene into COS-1 cells with a plasmid designated pEF-BOS/blmA, which contains a strong promoter from the human polypeptide chain elongation factor 1alpha, we transiently overproduced BLMA at a high level of approximately 4% of the whole cell protein. Although NIH/3T3 cells transfected with pEF-BOS/blmA, designated NIH/3T3-BR cells, stably expressed BLMA, its expression level was about 0.1% of the total protein. Using an anti-BLMA monoclonal antibody reported previously [Sugiyama et al. (1995) FEBS Lett. 362, 80-84], we revealed that BLMA is localized in the nucleus of pEF-BOS/blmA-transfected COS-1 and NIH/3T3-BR cells. Semi-permeabilized nuclear transport experiments showed that BLMA penetrates the nuclear envelope by energy- and transporter-independent passive diffusion, suggesting that the karyophilic nature of BLMA may be due to the acidic nature of the protein. NIH/3T3-BR cells were 130-fold more resistant to Bm than the host cells. NIH/3T3 cells exhibited a swollen nuclear envelope and a malformed spindle body and overexpressed at least 4 kinds of stress proteins including calreticulin and mitochondrial matrix protein P1 when exposed to 25 microg/ml of Bm, whereas NIH/3T3-BR cells grew without morphological alteration and expressed no stress proteins under the same conditions. Furthermore, reverse transcription-polymerase chain reaction and Northern blot analysis showed that the expression of interleukin-6, an inflammatory cytokine, is activated by addition of Bm in NIH/3T3 cells, but not in the NIH/3T3-BR cells. These results suggest that BLMA contributes to protection of mammalian cells from the inflammatory effect of Bm.