Tyrosine aminotransferase induction regulation variant in tissue culture

Glucocorticoid receptors and effects in human lymphoid and leukemic cells

A variety of human leukopathic diseases including human acute lymphoblastic leukemia are responsive to glucocorticoids in a varying proportion of cases. We identified specific glucocorticoid receptors in human acute lymphoblastic leukemia cells. Their presence or absence was well correlated with both in vivo and in vitro responsiveness of these target cells to glucocorticoids. These data suggest that knowledge of glucocorticoid receptor status in human acute lymphoblastic leukemia may aid in selecting patients for therapy. Furthermore, these receptors exhibit significant quantitative differences in various subtypes of human leukemia, with null-cell lymphoblastic leukemia having approximately three times the mean number of receptors per cell as T-cell leukemias. These differences in receptor levels are associated with major differences in complete remission duration independent of other prognosticators of response such as patient age, white count, and cell surface markers. Specific receptors for glucocorticoids can also be identified in normal human peripheral blood monocyte fractions including unpurified peripheral blood lymphocytes, T, and non-T subcomponents of circulating lymphocytes and circulating monocytes. By criteria of quantity, of binding affinity, and specificity, these receptors appear to be similar to other classical glucocorticoid receptors. Receptors in human peripheral blood lymphocytes may be induced threefold on a per cell basis by treatment with the mitogen phytohemagglutinin. This is associated with a marked increase in glucocorticoid responsiveness.

Somatic cell fusion in the study of glucocorticoid action

The basic phenomena of cell fusion and hybrid cell formation are briefly described and the potential of somatic cell hybridization in studies on the expression of differentiated cellular functions is discussed. The technique of cell hybridization has been applied to two types of cellular responses to glucocorticoids. The induction of specific proteins has been investigated in hybrids of inducible cells with uninducible cells. Most studies dealt with the liver-specific enzyme tyrosine aminotransferase, whose inducibility was extinguished in the majority of the hybrids between hepatoma and nonliver cells. However, upon chromosome segregation, inducibility reappeared in some of these hybrid cells. The current ideas about cellular control of inducibility are discussed. The other major glucocorticoid-responsive system investigated in cell hybridization studies consists of lymphoid cells which are killed when exposed to the steroid. Such sensitive cells were hybridized with several types of glucocorticoid-resistant lymphoid lines, and sensitivity was found to be dominant over resistence. Hybrids between sensitive and resistant lymphoid cells, however, showed an increase in the frequency at which resistance occurred as compared to the rate observed with the wild-type parental cells. No complementation to steroid sensitivity was found in hybrids between different types of resistant cells with defects in the glucocorticoid-specific receptor system.

Glucocorticoid binding proteins in myeloblasts of acute myelogenous leukemia

The myeloblasts of 16 patients with untreated acute myelogenous leukemia were examined for specific glucocorticoid binding proteins. In only 3 of the 16 patients were such high affinity receptors found. The presence of glucocorticoid binding protein activity was positively correlated with inhibition of macromolecular synthesis of myeloblasts in vitro whereas absence of binding protein activity was associated with lack of glucocorticoid inhibition of the cells. Since glucocorticoids appear efficacious in only a small fraction of cases of acute myelogenous leukemia, determination of glucocorticoid binding protein activity may provide assistance in planning chemotherapeutic regimens.

Genetic control of melanization: isolation and analysis of amelanotic variants from cultured melanotic melanoma cells

MELANOMA CELLS EXPRESS A PHENOTYPE THAT IS EASY TO RECOGNIZE: the synthesis of melanin. We used this marker to isolate clones of amelanotic variants from large populations of wild-type melanotic clones. Cloudman mouse melanoma (S91, clone M-3, CCL 53.1) was chosen as the parental line because the cells are highly pigmented, grow well as clones in soft agar, and fuse readily with Sendai virus. Subclones (10(7)) of this line were screened without prior mutagenesis, and nine amelanotic variants were isolated. The mutagen ethylmethanesulfonate increased the frequency of variants by three to four orders of magnitude. Wild-type cells had both basal and melanocyte stimulating hormone-inducible tyrosinase activities. The four amelanotic variants that we have examined to date all behaved similarly: they lost basal tyrosinase (EC 1.14.18.1; monophenol monooxygenase) activity but retained melanocyte stimulating hormone-inducible activity; they contained Stage-II melanosomes but no melanized melanosomes; they exhibited growth characteristics similar to those of wild-type cells in culture but produced fewer tumors in mice.

Regulation of tyrosine aminotrasferase activity in two liver-derived permanent cell lines

The regulation of tyrosine aminotransferase (TAT) activity has been examined in two liver-derived heteroploid cell lines. One (hepatoma tissue culture cells [HTC]) was derived from a hepatoma, the other (rat liver culture cells [RLC]) was derived from normal liver. The two cell lines show the following striking similarities in the control of this specific protein: (a) The kinetics of TAT induction by dexamethasone phosphate (DxP) are similar in randomly growing cells of both lines; (b) During mitosis and early G(1) phase of the cell cycle TAT activity cannot be induced by DxP in either cell line; (c) 2-3 h into G(1), when both lines become sensitive to inducer, basal enzyme activity declines to a new steady-state level; (d) Preinduced cells collected in mitosis show approximately twice the level of TAT activity as fully induced, randomly growing cultures and this activity is maintained in early G(1) with or without the inducer; and (e) Inhibition of RNA synthesis by 5 microg/ml of actinomycin D in preinduced, synchronized cells allows TAT activity to remain at constitutive levels throughout G(1), even in the absence of inducer. These results are presented in support of a previously described model which states that glucocorticoid hormones exert posttranscriptional control of the synthesis of specific proteins in mammalian cells.

Regulation of phosphoenolpyruvate carboxykinase and tyrosine transaminase in hepatoma cell cultures. 3. Comparative studies in H35, HTC, MH1C1 and RLC cells

The ability of N(6), O(2)'-dibutyryl cyclic AMP (DBcAMP) to regulate a number of metabolic events in four lines of cultured rat hepatomas has been examined. Although dexamethasone induces tyrosine transaminase in all four lines, DBcAMP induces this enzyme normally only in H35 cells. A slight increase in transaminase activity was seen with MH(1)C(1) cells and HTC cells, but no effect was detectable in RLC cells. In contrast, phosphoenolpyruvate carboxykinase activity is increased by both agents in H35 and MH(1)C(1) cells, but neither had any effect in HTC or RLC cells. DBcAMP caused a rapid inhibition of the growth rate and DNA synthesis and an increase in protein content in both H35 and MH(1)C(1) cells but not in HTC or RLC cells. The effect of DBcAMP on DNA synthesis in MH(1)C(1) cells could be reversed by deoxycytidine as is also the case with H35 cells. The resistance of HTC and RLC cells to DBcAMP was not due to reduced uptake or deacylation as judged by studies with [(3)H]DBcAMP. The cyclic nucleotide appears to enter the cells by passive diffusion as the intracellular concentration approaches that in the medium within 30-60 min. Possible explanations for the differential responses observed are discussed.

Glucocorticoid-binding proteins in human acute lymphoblastic leukemic blast cells

The first known step in steroid hormone action is the association of the steroid with specific cytoplasmic steroid-binding proteins (SBP). Using a competitive binding assay, we detected, quantified, and partially characterized such a SBP in cytosol from glucocorticoid-sensitive human lymphoblastic leukemic blasts. The affinity of steroids for the SBP was directly related to their known killing potency. For example, steroids without glucocorticoid effect such as androstenedione, etiocholanolone, and tetrahydrocortisol were unable to displace radiolabeled dexamethasone from the SBP in the binding reaction. The dose-response curve for in vitro inhibition of [(3)H]thymidine uptake in leukemic blasts correlated closely with the binding affinity of glucocorticoids to the SBP, providing additional support for an essential physiologic role for SBP in steroid action. SBP activity was either greatly diminished or absent in glucocorticoid-resistant cells. Six patients who intially had SBP in their blasts and were responsive to combinations of drugs including glucocorticoids no longer had SBP activity detectable at a time when they no longer responded to combinations of drugs including glucocorticoids. In vitro [(3)H]thymidine uptake was not inhibited by steroids in leukemic blast cells lacking SBP activity. Other patients who had received some antileukemic therapy including glucocorticoids and who still had SBP in their leukemic blasts, were still responsive to drug combinations that included glucocorticoids. This appears to be the first study demonstrating glucocorticoid receptors in a human tissue.