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Among the nuclear hormone receptors, the retinoid X receptors (RXRs) play a central role through their ability to heterodimerize with other members of this family of transcription factors, including retinoic acid (RA) and vitamin D (VD3) receptors. We have previously found that all-trans retinoic acid and 1 alpha, 25-dihydroxyvitamin D3 cooperate to induce monocytic differentiation of U937 human leukemic cells. Here the expression of RXR alpha protein in myelomonocytic cells was studied by immunodetection using polyclonal antibodies. RXR alpha was detected upon exposure of cells to VD3 and higher levels were found in cells treated by combinations of RA and VD3 under conditions where both agents synergized for inducing monocytic properties.

The lectin jacalin is mitogenic for CD4 expressing T lymphocytes, interacts with the CD4 molecule, and inhibits HIV infection of CD4+ cells. In the present study the effect of jacalin was tested on cells from the monocyte/macrophage lineage that also express the CD4 molecule. We used CD4+ promyelomonocytic U937 cells differentiated towards the monocytic/macrophage lineage with either a mixture of two physiological agents, retinoic acid (RA) and 1α,25-dihydroxyvitamin D3 (VD), or the exogenous drug phorbol myristate acetate (PMA). The cells resulting from these treatments differed in term of CD4 expression. We focused our attention on interleukin-6 (IL-6) production, which implies an activation of the cells differentiated along both pathways. In CD4+ RA/VD-treated cells, jacalin induced a 10-fold higher IL-6 secretion than did lipopolysaccharide (LPS). This jacalin-induced IL-6 production was inhibited by agents interacting with CD4 (anti-CD4 mAbs and HIV recombinant gp120) or by recombinant soluble CD4. In contrast, the CD4- PMA-differentiated U937 cells did not secrete any IL-6 upon jacalin treatment, while they demonstrated a response to LPS similar to that of the RA/VD-differentiated cells. Together with the fact that jacalin interacts with CD4, these results provide evidence of the involvement of a CD4 dependent pathway in IL-6 production. J. Leukoc. Biol. 55: 214–220; 1994.

We report the effect of CBS-211A, a synthetic retinoid analog, designed for topical eye administration, on the growth and differentiation of myelomonocytic cells. This compound was assayed alone or in combination with 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3), since we previously evidenced a synergism of retinoic acid (RA) and 1 alpha,25(OH)2D3 in the induction of U937 cell differentiation. Unlike RA, CBS-211A neither affected the growth of myelomonocytic cells nor differentiated them. Nevertheless, when it was associated with 1 alpha,25(OH)2D3, CBS-211A strongly potentiated the 1 alpha,25(OH)2D3-induced inhibition of U937 cell proliferation and caused a dramatic increase in their differentiation toward monocytes/macrophages. The co-inducing effect of CBS-211A was restricted to U937 cells. Our data suggest that CBS-211A may have therapeutic implications in the treatment of certain kinds of myelomonocytic leukemia. CBS-211A also provides an interesting tool to understand the mechanisms involved in the differentiation of myelomonocytic cells.

RA induces the differentiation of myeloid leukemic cells both from patients and cell lines . The fact that differentiated cells loose their pro-liferative capacity provides an efficient approach for the treatment of acute promyelocytic leukemia by RA. Moreover a therapeutic effect extended to other fonns of leukemia is expected by using an appropriate synergistic combination between RA and other cell differentiating agents such as the biologically active form of vitamin D, la,25-dihy-droxyvitamin D

Disease relapse sometimes occurs after acute promyelocytic leukemia (APL) therapy with all-trans retinoic acid (ATRA). Among the diagnostic parameters predicting relapse, heterogeneity in the in vitro differentiation rate of blasts is an independent factor. To identify biologic networks involved in resistance, we conducted pharmacogenomic studies in APL blasts displaying distinct ATRA sensitivities. Although the expression profiles of genes invested in differentiation were similarly modulated in low- and high-sensitive blasts, low-sensitive cells showed higher levels of transcription of ATRA-target genes, transcriptional regulators, chromatin remodelers, and transcription factors. In opposition, only high-sensitive blasts expressed the CYP26A1 gene, encoding the p450 cytochrome which is known to be involved in retinoic acid catabolism. In NB4 cells, ATRA treatment activates a novel signaling pathway, whereby interleukin-8 stimulates the expression of the homeobox transcription factor HOXA10v2, an effective enhancer of CYP26A1 transcription. These data were corroborated in primary APL cells, as maturation levels correlated with CYP26A1 expression. Treatment with a retinoic acid metabolism blocking agent (RAMBA) results in high-nucleoplasmic concentrations of retinoid and growth of NB4-resistant subclones. Hence, for APL blasts associated with poor prognosis, the low CYP26A1 expression may explain high risk of resistance installation, by increased retinoid pressure. Pharmacogenomic profiles of genes involved in retinoid acid metabolism may help to optimize anticancer therapies, including retinoids.

Using a differential display method to identify differentiation-related genes in human myelomonocytic U937 cells, we cloned the cDNA of a gene identical to Drg1 and homologous to other recently discovered genes, respectively human RTP and Cap43 and mouse Ndr1 and TDD5 genes. Their open reading frames encode proteins highly conserved between mouse and man but which do not share homology with other know proteins. Conditions in which mRNAs are up-regulated suggest a role for the protein in cell growth arrest and terminal differentiation. We raised antibodies against a synthetic peptide reproducing a characteristic sequence of the putative polypeptide chain. These antibodies revealed a protein with the expected 43 kDa molecular mass, up-regulated by phorbol ester, retinoids and 1,25-(OH)2 vitamin D3 in U937 cells. It was increased in mammary carcinoma MCF-7 cells treated by retinoids and by the anti-estrogen ICI 182,780 but not by 4-hydroxytamoxifen. The mouse Drg1 homologous protein was up-regulated by retinoic acid in C2 myogenic cells. The diversity of situations in which expression of RTP/Drg1/Ndr1 has now been observed shows that it is widely distributed and up-regulated by various agents. Here we show that ligands of nuclear transcription factors involved in cell differentiation are among the inducers of this novel protein.

The individual and combined effects of heat shock, all- trans retinoic acid and 1,25-dihydroxyvitamin D 3 on inhibition of cell growth and initiation of differentiation were investigated on U937 human leukemia cells. Incubation of U937 cells at 43°C for 1 h did not affect cell viability but induced a reduction of cell growth and the emergence of a differentiated phenotype, characterized by the acquisition of chemiluminescent responses to various oxidative burst inducers and by the capacity to produce IL-6 in response to bacterial lipopolysaccharide. Heat shock alone, therefore, appears to be an efficient inducer of cell differentiation. In addition, heat shock primed the cells to respond more efficiently to the action of retinoic acid and vitamin D, and amplified the phenotypic changes initiated by pretreatment of U937 cells with these agents.

The human-derived leukemia cell lines HL-60 and U937 are known to differentiate into more mature phagocytic cells in the presence of retinoic acid or 1,25-dihydroxyvitamin D3. We studied the effects of combinations of these two agents on cell growth and differentiation. These treatments were found to increase inhibition of cell proliferation. A dramatic enhancement of functional properties was observed in U937, but not HL-60 cells exposed to combinations of the two inducers. We investigated the conditions required to obtain the highest synergistic effects on the differentiation of U937 cells. These effects were found to be highly dose-dependent. We found that synergism required the simultaneous presence of both inducers and did not occur upon sequential exposure to each agent used separately.

It is now well established that all trans Retinoic Acid (atRA), administered at pharmacological doses to Acute Promyelocytic Leukemia (APL) patients, provides the first example of therapy by differentiation. Clinical remission is often transient as resistance develops. Because mechanisms of installation are still unclear, gene expression changes during APL cells differentiation were identified by Serial Analysis of Gene Expression (SAGE). Construction of proliferative and 48 hours atRA-treated NB4 cells libraries allowed us to identify a set of new transcriptional markers. Expression profiles of atRA response were performed on NB4, two atRA-resistant cell lines (NB4-LR2 and UF1) and APL blasts by real time PCR analyze on Microfluidic Card. We choose a hundred genes from multiple functional classes since there are several potential mechanisms for atRA resistance: target gene expression, transcription regulation, atRA metabolism, proteasome pathways≡ Reliability between SAGE and Microfluidic technologies is high since 95% of significantly modulated SAGE transcripts (p Transcriptome studies were conducted onto blast of patients with distinct long-term sensitivity, established by correlation to the in vitro differentiation rate (Cassinat, B. et al. Blood, 2001). As a result, all patients show transcriptional response to retinoid. However, once blast differentiation reached, induction of atRA-response element genes in high sensitive blasts is reduced. In opposition, transcripts expression of low sensitive patients is still high, revealing a delay in differentiation establishment. Conversely, expression of cytochrome p450 CYP26, involved in the atRA catabolism, is maintained in highly sensitive blast whereas no modulation is observed in low sensitive blast. Because promoter analysis reveals Homeobox response element, involvement of HOX factors found in SAGE librairies was investigated. In cell lines, HOX factors cooperate with retinoid receptors to increase CYP26 transcription. Furthermore, high-pressure chromatography shows a switch between atRA and its metabolites, 6 hours after atRA addition but only in sensitive cell line. To conclude, CYP26 is a relevant marker of resistance prognostic. Since metabolites show similar efficiency for cell growth inhibition and differentiation than atRA, their implication in resistance installation is investigated.

We have analysed Con A-stimulated mouse lymphocytes for the presence of 2′-5′-linked oligoadenylates using a radioimmunoassay based on a monoclonal antibody raised against adenylyl (2′-5′) adenosine (A2′pA). Time-course and Con A dose dependence were performed. We found that Con A induced, in a dose-dependant manner, the accumulation of immunoreactive material, together with the incorporation of 3H-thymidine in DNA. We showed that the immunoreactive material was constituted for the essential, by a novel 2′-5′ oligoadenylate. It was isolated and characterized as adenylyl 2′-5′adenylic acid (2′ and 3′P) according to the combination of criteria such as immunoreactivity, enzyme susceptibility, chromatographic behaviour and comparison with A2′pA3′(32P)p, A2′pA3′p acid A2′pA2′p that we have chemically synthetized. This is the first example of significant variations of a 2′-5′ oligoadenylate level in circumstances other than the antiviral mechanism of interferon.

Calf fetuin is a well-known glycoprotein found only in the fetus. A similar protein exists in fetal lamb serum but it had been demonstrated only by immunological methods. In the present investigation, we attempted the isolation and characterization of this protein. 1. 1. Fetal lamb serum was analysed by several electrophoretical methods. Its relative complexity does not allow the unambiguous identification of lamb fetuin. 2. 2. Using the alcohol-metal ion fractionation procedure of Spiro, it was possible to isolate a glycoprotein very similar to calf fetuin but in lower yields. Some contaminant proteins were observed. 3. 3. An alternative method is proposed (chromatography on CM-cellulose, pH 4.6, I = 0.01, followed by gel filtration on Sephadex G-200) leading to higher yields of a purer product. 4. 4. Some physicochemical parameters have been measured. E2781% = 4.05, s20,w0 = 3.50 ± 0.10; pHi = 3.85, 4.05, 4.10, 4.40 for the main variants. The apparent molecular weight measured by gel filtration is very much the same as for calf fetuin. 5. 5. The amino acid analyses revealed the presence of 364 residues per mole, representing approximately 79.8% of the weight of the protein. No methionine could be detected, nor any free -SH group, suggesting the presence of 6 disulfide bonds. 6. 6. The N- and C-terminal residues were both isoleucine. 7. 7. The carbohydrate content (approximately 22.75%) was determined by classical methods. Sialic acid (8.50%), is essentially N-acetylneuraminic acid. Hexosamines (6.75%) are glucosamine and galactosamine in the ratio 8:1. Hexoses are galactose (4.50%) and mannose (3.00%). 8. 8. The molecular weight calculated from chemical composition is 48 500. 9. 9. Calf and lamb fetuin appear to be very similar.