DR-nm23 expression affects neuroblastoma cell differentiation, integrin expression, and adhesion characteristics

BACKGROUND AND PROCEDURE

Nm23 gene family has been associated with metastasis suppression and differentiation. We studied DR-nm23 during neuroblastoma cells differentiation. DR-nm23 expression increased after retinoic acid induction of differentiation in human cell lines SK-N-SH and LAN-5.

RESULTS

In several cell lines, overexpression of DR-nm23 was associated with more differentiated phenotypes. SK-N-SH cells increased vimentin expression, increased deposition of collagen type IV, modulated integrin expression, and underwent growth arrest; the murine neuroblastoma cell line N1E-115 showed neurite outgrowth and a striking enhancement of beta1 integrin expression. Up-regulation of beta1 integrin was specifically responsible for the increase in the adhesion to collagen type I-coated plates. Finally, cells overexpressing DR-nm23 were unable to growth in soft agar.

CONCLUSIONS

In conclusion, DR-nm23 expression is directly involved in differentiation of neuroblastoma cells, and its ability to affects the adhesion to extracellular substrates and to inhibit growth in soft agar suggests an involvement in the metastatic potential of neuroblastoma.

DR-nm23 expression affects neuroblastoma cell differentiation, integrin expression, and adhesion characteristics

BACKGROUND AND PROCEDURE

Nm23 gene family has been associated with metastasis suppression and differentiation. We studied DR-nm23 during neuroblastoma cells differentiation. DR-nm23 expression increased after retinoic acid induction of differentiation in human cell lines SK-N-SH and LAN-5.

RESULTS

In several cell lines, overexpression of DR-nm23 was associated with more differentiated phenotypes. SK-N-SH cells increased vimentin expression, increased deposition of collagen type IV, modulated integrin expression, and underwent growth arrest; the murine neuroblastoma cell line N1E-115 showed neurite outgrowth and a striking enhancement of beta1 integrin expression. Up-regulation of beta1 integrin was specifically responsible for the increase in the adhesion to collagen type I-coated plates. Finally, cells overexpressing DR-nm23 were unable to growth in soft agar.

CONCLUSIONS

In conclusion, DR-nm23 expression is directly involved in differentiation of neuroblastoma cells, and its ability to affects the adhesion to extracellular substrates and to inhibit growth in soft agar suggests an involvement in the metastatic potential of neuroblastoma.

Neuroblastoma specific effects of DR-nm23 and its mutant forms on differentiation and apoptosis

DR-nm23 belongs to a gene family which includes nm23-H1, originally identified as a candidate metastasis suppressor gene. Nm23 genes are expressed in different tumor types where their levels have been alternatively associated with reduced or increased metastatic potential. Nm23-H1, -H2, DR-nm23 and nm23-H4 all possess NDP kinase activity. Overexpression of DR-nm23 inhibits differentiation and promotes apoptosis in hematopoietic cells. By contrast, it induces morphological and biochemical changes associated with neural differentiation in neuroblastoma cells. In this study, we show that mutations in the catalytic domain and in the serine 61 phosphorylation site, possibly required for protein-protein interactions, impair the ability of DR-nm23 to induce neural differentiation. Moreover, neuroblastoma cells overexpressing wild-type or mutant DR-nm23 are less sensitive to apoptosis triggered by serum withdrawal. By subcellular fractionation, wild-type and mutant DR-nm23 localize in the cytoplasm and prevalently in the mitochondrial fraction. In co-immunoprecipitation experiments, wild-type DR-nm23 binds other members of nm23 family, but mutations in the catalytic and in the RGD domains and in serine 61 inhibit the formation of hetero-multimers. Thus, the integrity of the NDP kinase activity and the presence of a serine residue in position 61 seem essential for the ability of DR-nm23 to trigger differentiation and to bind other Nm23 proteins, but not for the anti-apoptotic effect in neuroblastoma cells. These studies underline the tissue specificity of the biological effects induced by DR-nm23 expression.

The nucleoside diphosphate kinase activity of DRnm23 is not required for inhibition of differentiation and induction of apoptosis in 32Dcl3 myeloid precursor cells

DRnm23 belongs to a multigene family which includes nm23-H1, the first bona fide metastasis suppressor gene, nm23-H2, nm23-H4, and nm23-H5. Like nm23-H1, nm23-H2, and nm23-H4, DRnm23 possesses nucleoside diphosphate kinase (NDPK) activity. Upon overexpression in myeloid precursor 32Dcl3 cells, DRnm23 inhibits granulocytic differentiation and promotes apoptosis. Two specific mutants of DRnm23 (H134Q and S136P), at residues required for the NDPK activity, inhibit differentiation and promote apoptosis of 32Dcl3 cells. By contrast, substitution of serine 61 with proline (S61P) or deletion of the RGD domain (DeltaRGD) abrogates the effects of wild-type DRnm23. Like wild-type DRnm23, all four mutants show a predominantly mitochondrial subcellular localization. These studies indicate that the enzymatic activity of DRnm23 is not required for the effects observed in 32Dcl3 cells. Moreover, the inability of the S61P and DeltaRGD DRnm23 mutants to inhibit differentiation and promote apoptosis may be due to defective protein-protein interactions at the mitochondria, the predominant site of DRnm23 subcellular localization.

DR-nm23 gene expression in neuroblastoma cells: relationship to integrin expression, adhesion characteristics, and differentiation

BACKGROUND

Neuroblastoma, a childhood tumor originating from cells of the embryonic neural crest, retains the ability to differentiate, yielding cells with epithelial-Schwann-like, neuronal, or melanocytic characteristics. Since nm23 gene family members have been proposed to play a role in cellular differentiation, as well as in metastasis suppression, we investigated whether and how DR-nm23, a recently identified third member of the human nm23 gene family, might be involved in neuroblastoma differentiation.

METHODS

Three neuroblastoma cell lines (human LAN-5, human SK-N-SH, and murine N1E-115) were used in these experiments; cells from two of the lines (SK-N-SH and N1E-115) were also studied after being stably transfected with a plasmid containing a full-length DR-nm23 complementary DNA. Cellular expression of specific messenger RNAs and proteins was assessed by use of standard techniques. Cellular adhesion to a variety of protein substrates was also evaluated.

RESULTS

DR-nm23 messenger RNA levels in nontransfected LAN-5 and SK-N-SH cells generally increased with time after exposure to differentiation-inducing conditions; levels of the other two human nm23 messenger RNAs (nm23-H1 and nm23-H2) remained essentially constant. Transfected SK-N-SH cells overexpressing DR-nm23 exhibited some characteristics of differentiated cells (increased vimentin and collagen type IV expression) even in the absence of differentiation-inducing conditions. Compared with control cells, DR-nm23-transfected cells exposed to differentiation-inducing conditions showed a greater degree of growth arrest (SK-N-SH cells) and greater increases in integrin protein expression, especially of integrin beta1 (N1E-115 cells). DR-nm23-transfected N1E-115 cells also showed a marked increase in adhesion to collagen type I-coated tissue culture plates that was inhibited by preincubation with an anti-integrin beta1 antibody.

CONCLUSIONS

DR-nm23 gene expression appears to be associated with differentiation in neuroblastoma cells and may affect cellular adhesion through regulation of integrin protein expression.

Gene structure, promoter activity, and chromosomal location of the DR-nm23 gene, a related member of the nm23 gene family

DR-nm23 cDNA was cloned recently by differential screening of a cDNA library derived from chronic myelogenous leukemia-blast crisis primary cells. It is highly homologous to the putative metastasis suppressor nm23-H1 gene and the closely related nm23-H2 gene. When overexpressed in the myeloid precursor 32Dcl3 cell line, it inhibited granulocyte colony-stimulating factor-stimulated granulocytic differentiation and induced apoptosis. We have now found that the expression of DR-nm23 is not restricted to hematopoietic cells but is also detected in an array of solid tumor cell lines, including carcinoma of the breast, colon, and prostate, as well as the glioblastoma cell line T98G. We have also isolated both the gene and its 5'-flanking region and found that DR-nm23 localizes on chromosome 16q13. The gene consists of six exons and five introns. When fused in-frame to the nucleotide sequence for the green fluorescent protein and transfected in SAOS-2 cells, it generates a protein of the predicted size that localizes to the cytoplasm. The 5'-flanking region of DR-nm23 does not contain a canonical TATA box or a CAAT box, but it is G+C rich and contains two binding sites for the developmentally regulated transcription factor activator protein 2 (AP-2). Transient expression assays of DR-nm23 promoter-chloramphenicol acetyltransferase constructs demonstrated that the segment from nucleotides -1028 to +123 has the highest activity in hematopoietic K562 cells and in TK-ts13 hamster fibroblasts. Moreover, AP-2 induced a 3-fold transactivation of the DR-nm23 5'-flanking segment from nucleotides -1676 to +123 and interacted specifically with oligomers containing putative AP-2 binding sites (-936 to -909, and -548 to -519) as indicated by electrophoretic mobility shift assay. Furthermore, nuclear run-on assays from high and low DR-nm23-expressing cells (K562 and CCRF-CEM, respectively) revealed similar transcription rates. Therefore, the regulation of the DR-nm23 gene expression might involve other mechanisms occurring at posttranscriptional and/or translational levels.

Overexpression of DR-nm23, a protein encoded by a member of the nm23 gene family, inhibits granulocyte differentiation and induces apoptosis in 32Dc13 myeloid cells

Chronic myelogenous leukemia evolves in two clinically distinct stages: a chronic and a blast crisis phase. The molecular changes associated with chronic phase to blast crisis transition are largely unknown. We have identified a cDNA clone, DR-nm23, differentially expressed in a blast-crisis cDNA library, which has approximately 70% sequence similarity to the putative metastatic suppressor genes, nm23-H1 and nm23-H2. The deduced amino acid sequence similarity to the proteins encoded by these two latter genes is approximately 65% and includes domains and amino acid residues (the leucine zipper-like and the RGD domain, a serine and a histidine residue in the NH2- and in the COOH-terminal portion of the protein, respectively) postulated to be important for nm23 function. DR-nm23 mRNA is preferentially expressed at early stages of myeloid differentiation of highly purified CD34+ cells. Its constitutive expression in the myeloid precursor 32Dc13 cell line, which is growth-factor dependent for both proliferation and differentiation, results in inhibition of granulocytic differentiation induced by granulocyte colony-stimulating factor and causes apoptotic cell death. These results are consistent with a role for DR-nm23 in normal hematopoiesis and raise the possibility that its overexpression contributes to differentiation arrest, a feature of blastic transformation in chronic myelogenous leukemia.

Transcriptional regulation of two myeloid-specific genes, myeloperoxidase and lactoferrin, during differentiation of the murine cell line 32D C13

The transcriptional regulation of myeloperoxidase (MPO) and lactoferrin (LF) was examined during terminal myeloid differentiation of the murine cell line 32D C13. The rates of transcription initiation for MPO and LF, determined by an in vitro nuclear run-on assay, increased approximately ninefold. The accumulation of MPO mRNA in 32D C13 cells, determined by Northern blot analysis, correlated temporally with the observed increase in MPO transcription initiation. On the other hand, accumulation of LF mRNA lagged behind the observed increase in LF transcription initiation. In mouse L cells, the LF gene was transcribed more frequently than the MPO gene, though neither mRNA accumulated. Finally, murine MPO transcription is shown, by Northern blot and primer extension analysis, to initiate at multiple sites. These results indicate that whereas transcription induction may largely account for the accumulation of MPO mRNA during terminal myeloid differentiation, both transcriptional and posttranscriptional mechanisms operate to allow accumulation of LF mRNA. The 32D C13 cell system will be a useful model for elucidating these mechanisms.

Selective inhibition of leukemia cell proliferation by BCR-ABL antisense oligodeoxynucleotides

To determine the role of the BCR-ABL gene in the proliferation of blast cells of patients with chronic myelogenous leukemia, leukemia blast cells were exposed to synthetic 18-mer oligodeoxynucleotides complementary to two identified BCR-ABL junctions. Leukemia colony formation was suppressed, whereas granulocyte-macrophage colony formation from normal marrow progenitors was unaffected. When equal proportions of normal marrow progenitors and blast cells were mixed, exposed to the oligodeoxynucleotides, and assayed for residual colony formation, the majority of residual cells were normal. These findings demonstrate the requirement for a functional BCR-ABL gene in maintaining the leukemic phenotype and the feasibility of gene-targeted selective killing of neoplastic cells.

Antisense myb inhibition of purified erythroid progenitors in development and differentiation is linked to cycling activity and expression of DNA polymerase alpha

These studies aimed to determine the expression and functional role of c-myb in erythroid progenitors with different cycling activities. In the first series of experiments the erythroid burst-forming unit (BFU-E) and colony-forming unit (CFU-E) populations from adult peripheral blood (PB), bone marrow (BM), and embryonic-fetal liver (FL) were treated with either c-myb antisense oligomers or 3H-thymidine (3H-TdR). A direct correlation was always observed between the inhibitory effect of anti-myb oligomers and the level of cycling activity. Thus, the inhibitory effect of antisense c-myb on the number of BFU-E colonies was 28.3% +/- 15.8% in PB, 53.4% +/- 9.3% in BM, and 68.2% +/- 24.5% in FL. Both adult and embryonic CFU-E were markedly inhibited (73.2% +/- 10.4% and 74.2% +/- 12.7%). Using highly purified PB progenitors, we observed a similar pattern, although with slightly lower inhibitory effects. In the 3H-TdR suicide assay the killing index of BFU-E was 8.9% +/- 4.2% in PB, 29.4% +/- 6.5% in BM, and 40.1% +/- 9.6% in FL. The values for adult and embryonic CFU-E were 55.7% +/- 7.9% and 60.98% +/- 6.6%, respectively. We then investigated the kinetics of c-myb mRNA level during the erythroid differentiation of highly purified adult PB and FL BFU-E, as evaluated in liquid-phase culture by reverse transcription-polymerase chain reaction. Adult erythroid precursors showed a gradual increase of c-myb mRNA from day 4 through day 8 of culture and a sharp decrease at later times, whereas the expression of c-myb mRNA and protein in differentiation embryonic precursors peaked 2 days earlier. In both cases, c-myb mRNA level peaked at the CFU-E stage of differentiation. Finally, highly purified adult PB BFU-E were stimulated into cycling by a 3-day treatment with interleukin-3 in liquid phase: both the sensitivity to c-myb antisense oligomers and the 3H-TdR suicide index showed a gradual, strictly parallel increase. Under the same experimental conditions a progressive increase of the mRNA level of DNA polymerase alpha was observed. These observations suggest that in early erythroid differentiation c-myb activation is associated with the progression of progenitors into the S phase of the cell cycle, as well as to the synthesis of DNA polymerase alpha.

Normal and leukemic hematopoietic cells manifest differential sensitivity to inhibitory effects of c-myb antisense oligodeoxynucleotides: an in vitro study relevant to bone marrow purging

The c-myb protooncogene is preferentially expressed in hematopoietic cells, and its encoded protein, Myb, is required for hematopoietic cell proliferation. To analyze the relative Myb dependence of normal and leukemic human hematopoietic progenitor cells, normal bone marrow cells, several types of leukemic blast cells, and 1:1 mixtures of normal and leukemic cells were cultured in the presence of c-myb sense or antisense oligodeoxynucleotides; cell viability and cloning efficiency were then assessed. c-myb sense oligomers had negligible effects on normal and leukemic cells. In contrast, c-myb antisense oligomers strongly inhibited or completely abolished clonogenic growth of a T-cell leukemia line, 78% (18 of 23) of primary acute myelogenous leukemia cases examined, and 4 of 5 primary chronic myelogenous leukemia (CML) cases in blast crisis. In three of the latter patients, polymerase chain reaction analysis of a 1:1 mixture of c-myb antisense-treated normal and CML cells revealed a complete absence of bcr-abl expression, suggesting that the CML clonogenic units had been completely eliminated from the cultures. At antisense doses that inhibited leukemic cell growth, normal hematopoietic progenitor cells survived. Thus, normal and leukemic hematopoietic cells show differential sensitivity to the toxic effects of c-myb antisense DNA. Perturbation of c-myb function with antisense oligodeoxynucleotides might eventually form the basis for a molecular approach to leukemia therapy, perhaps most immediately as ex vivo bone marrow purging agents.

Down-regulated c-myb expression inhibits DNA synthesis of T-leukemia cells in most patients

We have investigated the functional relevance of c-myb expression for DNA synthesis in patients' T-leukemia cells. [3H]Thymidine incorporation assays of 32 patients' leukemia cells exposed in vitro to c-myb sense or antisense oligodeoxynucleotides served to define two groups of patients: a responder group whose leukemia cells showed 2- to 16-fold lower levels of [3H]thymidine incorporation in c-myb antisense-treated cultures than in c-myb sense-treated cultures (20 patients) and a nonresponder group whose cells showed comparable [3H]thymidine incorporation levels in either c-myb sense- or antisense-treated cultures (12 patients). Down-regulation of c-myb mRNA levels in cells exposed to c-myb antisense oligodeoxynucleotides was comparable in both groups of patients, indicating that differential sensitivity to c-myb antisense oligodeoxynucleotides was not due to differential uptake of these oligodeoxynucleotides. DNA polymerase alpha mRNA levels were down-regulated in cells from the responders but were unaffected in the nonresponder group. These results suggest that c-myb is required for DNA synthesis in cells of many but not all T-leukemia patients and that leukemia cells in which DNA synthesis is not inhibited despite down-regulation of c-myb expression may have undergone some genetic change(s) that obviate(s) the requirement for myb protein.

Inhibition of T-cell proliferation by a MYB antisense oligomer is accompanied by selective down-regulation of DNA polymerase alpha expression

We recently found that inhibition of MYB protein synthesis in human peripheral blood mononuclear cells (PBMC) exposed to human c-myb (designated MYB) antisense oligodeoxynucleotides prevents entry into S phase and cell proliferation. To determine the mechanism(s) by which down-regulation of human c-myb protein (MYB) synthesis interferes with DNA synthesis, we analyzed mRNA levels of DNA polymerase alpha and proliferating cell nuclear antigen (PCNA), transcripts of two genes required for DNA synthesis, in normal and leukemic T lymphocytes exposed to MYB antisense oligodeoxynucleotides. Expression of DNA polymerase alpha was inhibited both in normal T lymphocytes progressing from G0 to S phase and in exponentially growing CCRF-CEM leukemic cells, whereas expression of PCNA was inhibited only in mitogen-stimulated PBMC and remained essentially unaffected in the leukemia T-cell line. The functional link between expression of MYB and DNA polymerase alpha mRNAs was further demonstrated by analyzing DNA polymerase alpha mRNA levels in a temperature-sensitive (ts) fibroblast cell line (TK-ts13; TK is thymidine kinase) constitutively expressing human MYB mRNA driven by the simian virus 40 (SV40) promoter. In the MYB-expressing TK-ts13 cells, DNA polymerase alpha mRNA levels were unaffected following shift to the nonpermissive temperature of 39.6 degrees C, whereas in the parental line, DNA polymerase alpha mRNA levels were readily down-regulated. These findings indicate that the expression of MYB is related to that of DNA polymerase alpha in cells expressing MYB at high levels and suggest that there is a functional link between c-myb and DNA polymerase alpha mRNA expression during cell cycle progression of normal T lymphocytes.

Stage-related proliferative activity determines c-myb functional requirements during normal human hematopoiesis

To determine if MYB protein is preferentially required during specific stages of normal human hematopoiesis we incubated normal marrow mononuclear cells (MNC) with c-myb antisense oligodeoxynucleotides. Treated cells were cultured in semisolid medium under conditions designed to favor the growth of specific progenitor cell types. Compared with untreated controls, granulocyte-macrophage (GM) CFU-derived colonies decreased 77% when driven by recombinant human (rH) IL-3, and 85% when stimulated by rH GM colony-stimulating factor (CSF); erythroid burst-forming unit (BFU-E)- and CFU-E-derived colonies decreased 48 and 78%, respectively. In contrast, numbers of G-CSF-stimulated granulocyte colonies derived from antisense treated MNC were unchanged from controls, though the numbers of cells composing these colonies decreased approximately 90%. Similar results were obtained when MY10+ cells were exposed to c-myb antisense oligomers. When compared with untreated controls, numbers of CFU-GM and BFU-E colonies derived from MY10+ cells were unchanged, but the numbers of cells composing these colonies were reduced approximately 75 and greater than 90%, respectively, in comparison with controls. c-myc sense and antisense oligomers were without significant effect in these assays. Using the reverse transcription-polymerase chain reaction, c-myb mRNA was detected in developing hematopoietic cells on days 0-8. At day 14 c-myb expression was no longer detectable using this technique. These results suggest that c-myb is required for proliferation of intermediate-late myeloid and erythroid progenitors, but is less important for lineage commitment and early progenitor cell amplification.

Molecular mechanisms underlying erythropoiesis: cycling activity of adult BFU-e relates to their requirement for c-myb function and potential for HbF synthesis

Highly purified erythroid burst-forming units (BFU-e) from human embryonic liver, adult marrow and blood were manipulated in vitro by cytokine addition in order to explore their requirements for c-myb function and potential for fetal hemoglobin (HbF) synthesis, particularly as related to their cycling activity. c-myb is expressed at a minimal level and functionally required to a limited extent in quiescent adult BFU-e. However, c-myb is actively transcribed and stringently required for differentiation of actively cycling progenitors (embryonic BFU-e, embryonic and adult erythroid colony-forming units). The cycling activity of highly purified adult BFU-e, gradually enhanced by interleukin 3 (IL-3) addition, is strictly and directly related to both their functional requirements for c-myb and the level of myb mRNA expression in the progenitor population. It may be concluded that the transcriptional activity and the functional role of c-myb in early erythropoiesis are dependent upon the cycling activity of the erythroid progenitors. The reactivation of HbF synthesis in normal adult bursts, observed in the standard fetal calf serum-rich (FCS+) clonogenic system, is suppressed in cultures with a drastically limited growth of accessory cells (i.e., in FCS- or FCS+ Mo- conditions). In these cultures, addition of granulocyte/macrophage colony-stimulating factor (GM-CSF) or IL-3 induces a dose-related rise of gamma-chain synthesis, at least in part via a direct action at the BFU-e level. Preliminary studies involving priming of adult BFU-e with IL-3 in liquid phase suggest that the HbF potential is relatively low in quiescent BFU-e, but distinctly higher in actively cycling ones. It is postulated that the in vivo reactivation of HbF synthesis in bone marrow regeneration may be mediated via increased IL-3 and GM-CSF activity, leading to enhanced cycling and differentiation of BFU-e.

Lineage-specific requirement of c-abl function in normal hematopoiesis

Structural abnormalities of the c-abl proto-oncogene are found in hematopoietic cells of more than 90 percent of individuals with chronic myelogenous leukemia. Therefore c-abl may be important in normal as well as malignant hematopoiesis. Normal human hematopoietic progenitor cells were exposed to three different c-abl sense or antisense oligodeoxynucleotides, and the effects on myeloid and erythroid colony formation were examined. The c-abl antisense oligodeoxynucleotides inhibited myeloid, but not erythroid, colony formation. The c-abl sense oligodeoxynucleotides and bcr sense and antisense oligodeoxynucleotides were not inhibitory in this assay. These data show that c-abl is critical in normal myelopoiesis and may explain the relatively selective expansion of leukocytes in patients with chronic myelogenous leukemia.

G1/S transition in normal human T-lymphocytes requires the nuclear protein encoded by c-myb

Exposure of peripheral blood mononuclear cells (PBMC) to an 18-base c-myb antisense oligomer before mitogen or antigen stimulation resulted in almost complete inhibition of c-myb messenger RNA and protein synthesis and blockade of T lymphocyte proliferation. Expression of early and late activation markers, interleukin-2 receptor and transferrin receptor, respectively, by PBMC was unaffected by antisense oligomer exposure as was the expression of c-myc messenger RNA. In contrast, histone H3 messenger RNA levels and DNA content were selectively decreased. These results suggest that c-myb protein deprivation does not perturb T lymphocyte activation or early molecular events that may prepare the cell for subsequent proliferation. Rather, it appears to specifically block cells in late G1 or early S phase of the cell cycle.

Alteration of growth and differentiation factors response by Kirsten and Harvey sarcoma viruses in the IL-3-dependent murine hematopoietic cell line 32D C13(G)

32D C13(G) is an interleukin 3(IL3)-dependent non-tumorigenic murine hematopoietic cell line which undergoes terminal differentiation into granulocytes when exposed to granulocytic colony stimulating factor (G-CSF). Infections of 32D C13(G) cells with either Kirsten rat sarcoma virus or Balb murine sarcoma virus, both containing a v-ras oncogene, generates clones that can permanently grow in G-CSF without differentiation. 32D-Ki-ras cells show a heterogeneous morphology ranging from the promyelocytic to the myelocytic stage of differentiation, and express high levels of both myeloperoxidase (MPO) and lactoferrin (LF) mRNA. 32D-Ha-ras cells show a more immature phenotype and express MPO but no LF mRNA. The apparent differentiation block of both 32D Ki-ras and 32D Ha ras can be reversed by treatment with the chemical inducers retinoic acid, sodium butyrate or dimethylsulphoxide, which leads to terminal differentiation into granulocytes. When 32D-Ki-ras and 32D-Ha-ras cells are cultured in medium containing IL-3 they become adherent and express some monocyte-macrophage markers. Upon prolonged exposure to IL3, 32D-Ki-ras, but not 32D-Ha-ras, resume suspension growth. Both 32D-Ki-ras and 32D-Ha-ras rapidly die if grown in chemically defined medium in the absence of any growth factor and are non-tumorigenic in immunosuppressed mice. These findings indicate that ras activation may interfere with the normal response to growth and differentiation factors in cells of the granulocytic lineage. These alterations may represent a critical, although non-sufficient, step in leukemogenesis.

Prognostic significance of "short-term" effects of chemotherapy on MYC and histone H3 mRNA levels in acute leukemia patients

We have found that administration of chemotherapy alters expression of growth-regulated genes in leukemia blast cells. To determine if such changes might be correlated with therapeutic outcome, we studied steady-state mRNA levels of MYC and histone H3 in the leukemic blasts of patients just prior to and 24 hr after the administration of the first doses of antileukemic drug therapy. Among nine patients with acute myelogenous leukemia, mRNA levels of MYC and histone H3 were reduced in five patients, and hematologic remission was achieved in three of these individuals. No remission was obtained in the four patients without reduction in MYC and histone H3 mRNA. Among acute lymphocytic leukemia patients, the mRNA levels of MYC and/or histone H3 were reduced by the therapy in seven of nine patients. A complete hematologic remission was obtained in five of them, and a partial remission was obtained in the other two. No remission was obtained in the patients in which MYC and H3 mRNA levels were unaffected by the therapy. These studies are of interest because they suggest that a decrease in the mRNA levels of MYC and histone H3 24 hr after a single dose of antineoplastic drugs may predict which patients will achieve complete remission; lack of reduction in these mRNAs correlates with failure to achieve remission. In addition, these studies also provide further proof of the heterogeneity of altered growth regulation among human leukemias.

Philadelphia-positive chronic myeloid leukemia with a chromosome 22 breakpoint outside the breakpoint cluster region

In chronic myelogenous leukemia (CML) the reciprocal translocation resulting in the Philadelphia chromosome (Ph1) leads to the formation of a chimeric transcriptional unit carrying both c-abl and bcr genetic information whose transcript is a new fused mRNA of 8.5-kilobases (kb) and whose translational product is a 210-kD phosphoprotein with tyrosine kinase activity implicated in the pathogenesis of CML. Twenty patients affected by Ph1-positive CML were studied by Southern blot analysis with bcr. Unexpectedly, in three Ph1-positive patients, the breakpoint of chromosome 22 was located neither inside the bcr region nor 5' to it. Northern blot analysis of the RNAs of two of these patients showed the absence of a detectable 8.5-kb chimeric mRNA. In the third patient a chimeric mRNA was detected by a c-abl cDNA probe but failed to hybridize with a bcr cDNA probe and showed very low hybridization levels with further 5' bcr cDNA probes. The possibility is raised that in CML a breakpoint outside bcr might either still allow the formation of a chimeric mRNA, possibly through alternative splicing mechanisms, or might prevent the transcription of the chimera. In the latter case different molecular events resulting in the formation of a Ph1 chromosome may underlie the same myeloid neoplastic phenotype.

Expression of c-myb protooncogene and other cell cycle-related genes in normal and neoplastic human colonic mucosa

The expression of c-myb, c-myc, histone H3, and ornithine decarboxylase genes was examined by Northern blot analysis in the normal and neoplastic mucosa of ten subjects affected by colon cancer. The mRNA levels of c-myb protooncogene were detected at low levels in all normal samples but were increased in the neoplastic mucosa of six cases in comparison to the normal counterpart. In five of these six cases the mRNA levels of c-myc, histone H3, and ornithine decarboxylase mRNAs were also increased, suggesting that there is a relation between the high expression of c-myb and the fraction of cycling neoplastic cells.

Simultaneously increased expression of the c-myc and mu chain genes in the acute blastic transformation of a chronic lymphocytic leukaemia

A B-cell chronic lymphocytic leukaemia terminated, 5 years from the onset, with a blast crisis. Karyotype analysis showed that the terminal lymphoblastic population evolved from the original B lymphocytic clone. The levels of expression of several oncogenes, as well as the mu chain gene, were assayed by Northern blot hybridization analysis of RNA extracted from the lymphoid populations before and after the 'acute transformation'. A seven- to eight-fold increase in the expression of c-myc and mu chain genes was observed in the blast population. c-myb, c-fes, c-Haras were not expressed either before or after the blastic transformation.

Expression of growth-regulated genes in human acute leukemias

We have investigated the expression of six growth-regulated genes (c-myc, c-myb, p53, 4F1, 2F1, and ornithine decarboxylase) and the S-phase-specific histone H3 gene in acute myeloid and lymphoid leukemic cells. We have purposely chosen three growth-regulated protooncogenes that share similar biological features and three gene sequences that have in common the cell cycle dependence of their expression in cells of different tissue and in different species. The level of expression was determined by measuring the amounts of specific RNA by Northern blot analysis. Levels of expression of the six growth-regulated genes were compared to the level of expression of the S-phase-specific H3 gene and among themselves. This method distinguishes the increased expression of a growth-regulated gene due to a true altered activation from over-expression which simply reflects an increase in the fraction of cycling cells. We have found that six of 14 patients with acute leukemias have markedly high ratios of c-myc/H3, c-myc/p53, and c-myc/c-myb expression. Two patients with altered c-myc expression have also a high ratio p53/H3. Within the group of cell cycle-dependent genes the ratios of expression seem in the overall much more regular with the clear exception of a patient with acute myelogenous leukemia in which the ratios 4F1/H3 and 2F1/H3 are significantly increased. A possible interpretation of these findings is that the fraction of noncycling leukemic cells that often constitute the majority of the entire leukemic population is in some cases in a true resting state, whereas in other cases heterogeneous degrees of growth arrest might occur. The altered expression of c-myc seems the feature most commonly associated with this putative growth arrest of leukemic cells suggesting that this gene may contribute to the impairment of proliferative control that is associated with the leukemic phenotype.

Altered expression of G1-specific genes in human malignant myeloid cells

We have studied the expression of cell-cycle genes specific to the G1 (2A9, 2F1, 4F1, c-myc) and S (histone H3) phases of the cell cycle in normal and malignant human myeloid cycling cells. The levels of expression were determined by measuring the amounts of specific RNA in blot hybridization assays. Levels of expression of the G1 genes were compared to the level of expression of the S-phase-specific H3 gene. This method can distinguish whether an increased expression of G1 genes is truly due to deregulation or simply reflects an increase in the fraction of proliferating cells. In a normal asynchronous system provided by the bone marrow cells of three normal donors, the expressions of the four G1-specific genes 2A9, 2F1, 4F1, and c-myc, and of the S-phase-specific gene H3 were in ratios that differed little from one individual to another. In the total RNA of eight patients in the chronic phase of chronic myelogenous leukemia, a high level of expression of G1 cell-cycle genes was paralleled by a high level of expression of the S-phase H3 gene, simply reflecting an increase in the fraction of proliferating cells. In patients with acute myelogenous leukemia (AML), the RNA levels of 2F1 and 4F1 paralleled the expression of H3-i.e., the ratios of expression 2F1/H3 and 4F1/H3 were the same as in normal bone marrow cells. However, in 9 of 10 patients with AML we found that the expression of c-myc was elevated with respect to H3 expression. The expression of 2A9 (with respect to H3) was also elevated in some of these AML patients. Two important conclusions can be drawn from these findings: increased levels of a G1-specific RNA in a tumor may not indicate overexpression of that gene but may instead simply reflect the fraction of proliferating cells; and in some patients with AML, however, the expression of certain G1 genes is truly deregulated and might contribute to the impairment of proliferative control that is associated with this phenotype.

Cellular levels of mRNA from c-myc, c-myb and c-fes onc-genes in normal myeloid and erythroid precursors of human bone marrow: an in situ hybridization study

The expression of three onc-genes, c-myc, c-myb and c-fes, has been evaluated at the cellular level in myeloid and erythroid precursors of normal human bone marrow, by "in situ" hybridization with tritium-labelled probes. A relatively large amount of m-RNA from the three onc-genes was detected in myeloblasts and promyelocytes, but whereas the expression of c-myc and c-myb decreased in more advanced stage of maturation of the myeloid lineage, c-fes mRNA remained at a relatively high level until the granulocyte stage. c-myc and c-myb were expressed at a fairly high level in basophilic erythroblasts, which also showed low levels of c-fes mRNA. No expression of these onc-genes was detectable in more mature erythroblasts. Megakaryocytes showed high levels of m-RNA from all three onc-genes. Our results suggest that c-myc and c-myb expression is related in some way to the cellular proliferation of myeloid and erythroid precursors, whereas c-fes expression is more restricted to myeloid differentiation.

Differential patterns of expression of cell cycle-related genes in blast cells of acute myeloid leukemia

The expression of two G1-specific clones, p2A9 and p4F1, of two cell cycle-related oncogenes, c-myc and c-myb and of one S phase-specific gene, the H3 histone gene, was explored in 11 cases of acute myeloid leukemia. Both Northern blot analysis and in-situ hybridization were employed. Differential patterns of gene expression were observed. In 6 out of 11 cases a considerable or high expression of the p2A9 and p4F1 clones and of c-myc and c-myb oncogenes was observed. In 2 cases a high expression of c-myc was matched by low or absent expression of the other genes examined. In 3 cases the expression of 2A9, 4F1, c-myc and c-myb was very low or undetectable. In two of these cases a considerable expression of the H3 histone gene was observed.

Activation of c-myb expression by phytohemagglutinin stimulation in normal human T lymphocytes

The expression of c-myb in normal human T lymphocytes directly derived from a normal subject and not adapted to continuous growth in culture was found to be markedly increased after phytohemagglutinin stimulation. In the same cells, the expression of c-myc mRNA is a much earlier event compared with the appearance of c-myb mRNA, which takes place soon after that of histone H3 mRNA. The increase in c-myb expression was not due to a particular T-lymphocyte subset, as shown by in situ hybridization assays.

Study of the levels of expression of two oncogenes, c-myc and c-myb, in acute and chronic leukemias of both lymphoid and myeloid lineage

Total cellular RNA from a series of leukemic cell populations, both myeloid and lymphoid, as well as from normal circulating lymphocytes was analysed for the expression of two cellular oncogenes, c-myc and c-myb, by Northern blot hybridization assay. Expression of c-myc but not of c-myb was observed in unstimulated normal lymphocytes. Stimulation by PHA was shown to activate the expression of both genes. Remarkably different levels of expression of c-myc were observed in ALL, whereas in CLL the expression of c-myc was uniformly low or absent. Differential expression of c-myc was detected in AML as well as in CML, c-myb was differentially expressed in AML and ALL, and absent in CLL and CML. Other single cases of hemopoietic disorders were studied, but the expression of the two oncogenes was low or absent. Neither evident genome amplification nor genome rearrangements were detected in the cell DNAs digested with restriction endonucleases.

Expression of human c-fes onc-gene occurs at detectable levels in myeloid but not in lymphoid cell populations

Total cellular RNA from a variety of myeloid and lymphoid cell populations, normal and leukaemic, was analysed for the expression of a human cellular onc-gene, c-fes, by northern blot hybridization assays. The probe used was a molecularly cloned human DNA sequence homologous to the 5' terminal sequence of v-fes. All the myeloid cellular populations expressed the c-fes gene. In some cell populations at an advanced stage of differentiation (circulating leucocytes from Chronic myeloid leukaemia (CML), HL60 cells induced to differentiate by retinoic acid) the level of expression was even higher than in early stages of the myeloid lineage (blast cells from AML, uninduced HL60 cells). No transcript of the c-fes gene was detected in the different lymphoid populations studied. The occurrence of an RNA complementary to the c-fes sequence appears sufficiently characteristic of a myeloid population to distinguish it from a lymphoid population, normal and leukaemic.

5'-Nucleotidase activity in liver homogenates of rats treated with CCl4, colchicine, cycloheximide, emetine, ethanol, ethionine and 5-fluorotryptophan

5'-Nucleotidase activity an enzyme marker of the plasma membranes, increases in female rat liver homogenates following ethionine administration, while homogenates from males show no changes. Treatment with CCl4, colchicine, cycloheximide, emetine, ethanol and 5-fluorotryptophan does not significantly modify the 5'-nucleotidase activity of liver homogenates of either female or male rats.