A mouse leukemia cell mutant resistant to blasticidin S

Chinese hamster cell variants resistant to the A chain of ricin carry altered ribosome function

Ricin, a toxic lectin from Ricinus communis, is composed of two different polypeptide chains, A and B, and the ricin A chain (RA) blocks protein synthesis. We studied cell lines resistant to cytotoxic action of RA. One low-RA-resistant cell line, AR10, isolated from Chinese hamster ovary (CHO) cells, was resistant to a low dose of RA (1 microgram/ml) and showed a 10-fold-higher resistance to RA and ricin than that of CHO. We further mutagenized AR10 to isolate high-RA-resistant cell lines AR100-6, AR100-9, and AR100-13, which were resistant to higher doses of RA and ricin (100- to 1,000-fold) than CHO was. The binding of [125I]ricin to AR10, AR100-6, AR100-9, and AR100-13 cells was decreased to about 30% of that of CHO. The internalization of [125I]ricin in AR10 cells and in the high-RA-resistant clones was the same. Polyuridylate-dependent polyphenylalanine synthesis, using S-30 extracts from either AR100-9 or AR100-13, was about 100-fold more resistant to the inhibitory action of RA than when CHO, AR10, and AR100-6 cells extracts were used. The protein synthesis with ribosomes (80S) from AR100-9 or AR100-13 was 10- to 100-fold more resistant to RA than it was with parental ribosomes when combined with the S-100 fraction of CHO cells. The polyphenylalanine synthesis assay using the ribosomes constituted from the 60S subunit of AR100-9 and the 40S subunit of CHO indicated that the resistant phenotype of AR100-9 cells is due to an alteration of the 60S ribosomal subunit.

Chinese hamster cell variants resistant to the A chain of ricin carry altered ribosome function

Ricin, a toxic lectin from Ricinus communis, is composed of two different polypeptide chains, A and B, and the ricin A chain (RA) blocks protein synthesis. We studied cell lines resistant to cytotoxic action of RA. One low-RA-resistant cell line, AR10, isolated from Chinese hamster ovary (CHO) cells, was resistant to a low dose of RA (1 microgram/ml) and showed a 10-fold-higher resistance to RA and ricin than that of CHO. We further mutagenized AR10 to isolate high-RA-resistant cell lines AR100-6, AR100-9, and AR100-13, which were resistant to higher doses of RA and ricin (100- to 1,000-fold) than CHO was. The binding of [125I]ricin to AR10, AR100-6, AR100-9, and AR100-13 cells was decreased to about 30% of that of CHO. The internalization of [125I]ricin in AR10 cells and in the high-RA-resistant clones was the same. Polyuridylate-dependent polyphenylalanine synthesis, using S-30 extracts from either AR100-9 or AR100-13, was about 100-fold more resistant to the inhibitory action of RA than when CHO, AR10, and AR100-6 cells extracts were used. The protein synthesis with ribosomes (80S) from AR100-9 or AR100-13 was 10- to 100-fold more resistant to RA than it was with parental ribosomes when combined with the S-100 fraction of CHO cells. The polyphenylalanine synthesis assay using the ribosomes constituted from the 60S subunit of AR100-9 and the 40S subunit of CHO indicated that the resistant phenotype of AR100-9 cells is due to an alteration of the 60S ribosomal subunit.

Isolation and characterization of puromycin-resistant clones from cultured mosquito cells

We have isolated from an established Aedes albopictus (mosquito) cell line clones which are resistant to the antibiotic puromycin. On the basis of growth and plating efficiency, clones Pur-8026 and Pur-8612 were five- and seven-fold more resistant, respectively, to puromycin than wild-type cells. In vitro protein synthesis was resistant to puromycin only in extracts prepared from Pur-8612 cells. Measurements of puromycin transport, cross-resistance to colchicine, and sensitivity to Tween-80 indicating that resistance in Pur-8026 cells was due to membrane alteration(s) affecting permeability to puromycin. This is the first description of puromycin resistant in insect cells and also the first report of puromycin resistance in an animal cell variant associated with an alteration at the level of protein synthesis.

Pactamycin resistance in CHO cells: morphological changes induced by the drug in the wild-type and mutant cells

Stable mutants resistant to pactamycin (PacR), a polypeptide chain initiation inhibitor, have been selected in a single step in Chinese hamster ovary (CHO) cells. The sensitivity of protein synthesis in mutant cell extracts to pactamycin indicates that resistance involves an alteration in the permeability of this drug. The failure of PacR mutants to show cross-resistance to other compounds provides further indication that the lesion is presumably specific for pactamycin. Cell hybrids formed between PacR X PacS lines show intermediate sensitivity towards pactamycin, suggesting that the PacR lesion behaves codominantly under these conditions. In the presence of subinhibitory concentrations of pactamycin, CHO cells, which are normally short, polygonal and disoriented, became greatly elongated and aligned themselves in parallel fashion to produce highly oriented colony morphologies, reminiscent of normal diploid fibroblasts. This effect of pactamycin on cellular morphology was seen much more clearly with the PacR mutants, although somewhat higher concentrations of the drug were required to produce this change.

The cross-resistance of mouse blasticidin S-resistant cell lines to puromycin and sparsomycin, inhibitors of ribosome function

The antibiotic blasticidin S inhibits peptide-chain elongation in extracts of bacteria and mammalian cells. After spontaneous or nitrosoguanidine mutagenesis, we have isolated 46 blasticidin S-resistant (Blar) cell lines independently from mouse mammary carcinoma cells (FM3a). Among those Blar clones, we studied two clones, a spontaneously induced one (S501) and a nitrosoguanidine mutagenized one (N742) in more detail. The resistant phenotype of these Blar cells is retained without change for at least four months in the absence of the antibiotic. These Blar cells are 10- to 20-fold more resistant to the cytotoxic action of the antibiotic than their parental cells in vivo. Polyuridylate dependent polyphenylalanine synthesis in vitro with S-30 extracts either from N742 or S501 is 10- to 50-fold more resistant to the inhibitory action of blasticidin S compared to the parental FM3a cells. Ribosomes from FM3a and N742 are fractionated into 40-S and 60-S subunits, and polyphenylalanine synthesis by mixing them in various combinations with S-100 fraction from mouse leukemia L5178Y cells indicating that the resistant phenotype of Blar cells is due to the alteration of 60 S ribosomal subunit. We also found that these two Blar cell lines (N742 and S501) show cross-resistance to gougerotin, puromycin and sparsomycin, but not to emetine or cycloheximide. The polyribosomal pattern of FM3a (Blas) and N742 was compared when the cells were incubated with 3 microgram/ml puromycin for 6 h. Puromycin treatment of Blas cells induced accumulation of monosomes and ribosomal subunits, while little if any transition of polyribosomes into monosome and ribosomal subunits appeared in its counterpart N742 treated with the same dose of puromycin.

The synthesis and degradation of presumptive messenger RNA in cultured mouse leukemia cells during the inhibition of protein synthesis

RNA synthesis in mouse leukemia L5178Y cells was inhibited depending upon the time of treatment by blasticidin S or by ricin, which inhibits specifically protein synthesis. When blasticidin S or ricin blocked protein synthesis by more than 90% of the control, marked accumulation of monosome was accompanied by the decrease of pulse-labeled RNA (20% of that in the control) in the polysomes and monosome fraction. The size distribution of pulse-labeled RNA among polysomal fractions including monosome obtained from the cells treated with either blasticidin S, ricin of L-asparaginase showed that the size of presumptive mRNA was shifted from 18 S to 9--10 S. TReatment of a blasticidin S-resistant (Bla-R) subline derived from L5178Y cells (Kuwano, M., Matsui, K., Takenaka, K., Akiyama, S. and Endo, H. (1977) Int. J. Cancer 20, 296--302) with L-asparaginase or ricin induced smaller size (9--10 S) RNA, but treatment of Bla-R cells with blasticidin S did not. Such shorter RNA fragments could not be observed even when cellular protein synthesis was inhibited by treatment for short time with blasticidin S (40--80% of the control activity). Smaller RNA fragments accumulated after drastic inhibition of protein synthesis were composed of 74% of polyadenylate sequence lacking poly(A)(-)RNA with peak of approx. 10 S and 26% of polyadenylate sequence containing poly(A)(+)RNA with a peak of 18 S, whereas cytoplasmic polysomal RNA of the control contained 46% poly(A)(+) with a peak of 18 S and 54% poly(A)(-)RNA with a 10--18 S peak. Cytoplasmic poly(A)(+)RNA degraded biphasically with half-lives of approx. 2 h and 8--10 h in exponentially growing mouse cells. However, in degradation of poly(A)(+)RNA molecules being formed in the cells pretreated with blasticidin S for 3 h, the rapid phase of decay with a half-life of approx. 2 h was interrupted by successively appearing poly(A)(+)RNA with a longer half-life of 8--10 h in cytoplasm. However, when the cells were pretreated with blasticidin S for 6 h, there appeared no poly(A)(+)RNA population with the rapid-decay in cytoplasm.

Isolation and characterization of amphotericin B-resistant cell lines in Chinese hamster cells

Amphotericin B is a polyene macrolide antibiotic which interacts specifically with sterols in mammalian cell membranes. Amphotericin B-resistant (AMBr) lines of stable phenotype have been isolated from cultured Chinese hamster (V79) cells. Three AMBr clones (AMBr-1, -2 and -3) isolated independently after treatment with nitrosoguanidine were resistant to greater than or equal to microgram/ml of the antibiotic, while DNA synthesis as well as the colony-forming ability of the parental V79 cells was blocked by greater than 80% of control in the presence of 20--50 microgram/ml amphotericin B. The AMBr cell line also exhibited increased resistance to other polyene macrolide antibiotics such as nystatin and pentamycin. Other agents, however, such as cytosine arabinoside or ricin, blocked DNA synthesis in AMBr cells to the same extent as in V79 cells. The amphotericin B resistance phenotype was stably retained even after AMBr cells were cultured in the absence of the drug for over 200 generations. The control of free cholesterol or its esters was significantly decreased in all three resistant clones. Furthermore, cholesterol synthesis from acetate as well as mevalonate was partly defective in AMBr cells, compared with that in V79 cells.