Effects in cancer cells of the recombinant l-Methionine Gamma-Lyase from Brevibacterium aurantiacum. Encapsulation in human erythrocytes for sustained l-Methionine Elimination
Résumé
Methionine deprivation induces growth arrest and death of cancer cells. To eliminate L-methionine we produced, purified, and characterized the recombinant pyridoxal 59-phosphate (PLP)-dependent L-methionine g-lyase (MGL) BL929 from the cheese-ripening Brevibacterium aurantiacum. Transformation of an Escherichia coli strain with the gene BL929 from B. aurantiacum optimized for E. coli expression led to production of the MGL-BL929. Elimination of L-methionine and cytotoxicity in vitro were assessed, and methylation-sensitive epigenetics was explored for changes resulting from exposure of cancer cells to the enzyme. A bioreactor was built by encapsulation of the protein in human erythrocytes to achieve sustained elimination of L-methionine in extracellular fluids. Catalysis was limited to alpha, gamma-elimination of L-methionine and L-homocysteine. The enzyme had no activity on other sulfur-containing amino acids. Enzyme activity decreased in presence of serum albumin or plasma resulting from reduction of PLP availability. Elimination of L-methionine induced cytotoxicity on a vast panel of human cancer cell lines and spared normal cells. Exposure of colorectal carcinoma cells to the MGL-BL929 reduced methylCpG levels of hypermethylated gene promoters including that of CDKN2A, whose mRNA expression was increased, together with a decrease in global histone H3 dimethyl lysine 9. The MGL-erythrocyte bioreactor durably preserves enzyme activity in vitro and strongly eliminates L-methionine from medium.