Suppression of telomerase activity in leukemic cells by mutant forms of Rhodospirillum rubrum L-asparaginase

Abstract

Active and stable mutant forms of short chain cytoplasmic L-asparaginase type I of Rhodospirillum rubrum (RrA) (RrA_{+N17, D60K, F61L}, RrA_{+N17, A64V, E67K}, RrA_{+N17, E149R, V150P}, Rr_{AE149R, V150P} and RrA_{E149R, V150P, F151T}) have been obtained by the method of site-directed mutagenesis. The variants RrA_{E149R, V150P, F151T} and RrА_{+N17, E149R, V150P} could decrease reduce expression of the hTERT telomerase subunit and, therefore, activity of telomeres in Jurkat cells, but not in cellular lysates. At the same time, L-asparaginasеs of Escherichia coli, Erwinia carotovora, and Wolinella succinogenes, mutant forms RrА_{+N17, D60K, F61L} and RrА_{+N17, A64V, E67K} did not suppress telomerase activity. It is suggested that some regions in the RrA structure (amino acids residues 146–164, 1–17, 60–67) are responsible for suppression of telomerase activity. The results obtained show that antineoplastic activity of some RrA variants is associated both with reduction of concentration of free L-asparagine, and with decreased expression of the hTERT telomerase subunit; this opens new prospects for antineoplastic therapy.