Post-transplant lymphoproliferative disorders: determination of donor/recipient origin in a large cohort of kidney recipients

Although in previous studies most post-transplant lymphoproliferative disorders (PTLD) were reported to derive from recipient cells, some cases derived from donor lymphocytes have been reported. To provide a better description of the features and outcome of PTLD according to the origin of the lymphoma, we performed histologic and molecular studies of PTLD in kidney recipients. Forty-three specimens were analyzed by histochemistry, fluorescent hybridization of the Y chromosome and analysis of multiple short tandem repeat microsatellite loci. Sixteen tumors were shown to be of donor origin and 27 of recipient origin. Time to PTLD was shorter in donor-derived PTLDs (20 ± 27 vs. 69 ± 67 months, p = 0.013). Ten-year patient survival was similar among patients with recipient- and donor-derived PTLD, but when PTLD-related mortality was analyzed, there was a trend to better survival in patients with donor lymphomas. Among the 21 PTLDs localized in the allograft, 14 lymphomas were of donor origin and seven of recipient origin. No difference was found between the two groups. Our analysis of the origin of PTLDs in the largest cohort studied to date with a description of the clinical and histological characteristics of donor and recipient PTLDs should lead to a better understanding of lymphomagenesis.

EGFR-TKI and lung adenocarcinoma with CNS relapse: interest of molecular follow-up

The epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) erlotinib improves survival of lung cancer as second- or third-line therapy. However, after an initial response, most patients will recur, particularly within the central nervous system. The present study reports the case of a 27-yr-old nonsmoking male presenting with a metastatic lung adenocarcinoma with EGFR exon 19 deletion, associated with sensitivity to EGFR-TKI. Gefitinib, followed by chemotherapy and finally erlotinib resulted in prolonged disease control, until multiple liver metastases were detected. After stopping EGFR-TKI, brain metastases with carcinomatous meningitis were diagnosed. A secondary T790M mutation, associated with resistance to EGFR-TKI, was found on the liver biopsy but not in the cerebrospinal fluid. Erlotinib was reintroduced and allowed a quick neurological improvement, even though the extra-cranial disease remained resistant to erlotinib. The present report underscores the interest of molecular monitoring in lung cancer. Persistent cerebral tyrosine kinase inhibitor sensitivity should be considered in patients presenting with an early central nervous system relapse after stopping epidermal growth factor receptor tyrosine kinase inhibitor, even with a T790M-resistant mutation in noncerebral metastases. Questions remain concerning the selection of sub-clones during epidermal growth factor receptor tyrosine kinase inhibitor therapy, which could differ according to metastatic sites, especially in the central nervous system.

Detection of K-Ras mutations in tumour samples of patients with non-small cell lung cancer using PNA-mediated PCR clamping

Non-small cell lung cancers (NSCLC), in particular adenocarcinoma, are often mixed with normal cells. Therefore, low sensitivity of direct sequencing used for K-Ras mutation analysis could be inadequate in some cases. Our study focused on the possibility to increase the detection of K-Ras mutations in cases of low tumour cellularity. Besides direct sequencing, we used wild-type hybridisation probes and peptide-nucleic-acid (PNA)-mediated PCR clamping to detect mutations at codons 12 and 13, in 114 routine consecutive NSCLC frozen surgical tumours untreated by targeted drugs. The sensitivity of the analysis without or with PNA was 10 and 1% of tumour DNA, respectively. Direct sequencing revealed K-Ras mutations in 11 out of 114 tumours (10%). Using PNA-mediated PCR clamping, 10 additional cases of K-Ras mutations were detected (21 out of 114, 18%, P<0.005), among which five in samples with low tumour cellularity. In adenocarcinoma, K-Ras mutation frequency increased from 7 out of 55 (13%) by direct sequencing to 15 out of 55 (27%) by clamped-PCR (P<0.005). K-Ras mutations detected by these sensitive techniques lost its prognostic value. In conclusion, a rapid and sensitive PCR-clamping test avoiding macro or micro dissection could be proposed in routine analysis especially for NSCLC samples with low percentage of tumour cells such as bronchial biopsies or after neoadjuvant chemotherapy.

Primary tumour genetic alterations and intra-tumoral heterogeneity are maintained in xenografts of human colon cancers showing chromosome instability

Evaluation of the role of clonal heterogeneity in colon tumour sensitivity/resistance to drugs and/or in conferring metastatic potential requires an adequate experimental model in which the tumour cells maintain the initial genetic alterations and intra-tumoral heterogeneity through maintenance of the genetic clones present in the initial tumour. Therefore, we xenografted subcutaneously into nude mice seven human colonic tumours (from stages B1 to D) that showed chromosome instability and transplanted them sequentially for up to 14 passages. Maintenance after xenografting of the genetic alterations present in the initial tumours was scored by allelotype studies targeting 45 loci localized on 18 chromosomes. We show that xenografting does not alter the genetic or the histological profiles of the tumours even after 14 passages. Screening of the entire genome of one tumour by comparative genome hybridization also showed overall stability of the alterations between the initial and the xenografted tumour. In addition, intra-tumoral heterogeneity was maintained over time, suggesting that no clonal selection occurred in the nude mice. The observation that some loci showed partial allelic imbalance in the initial tumour but loss of heterozygosity after the first passage in nude mice when all the normal cells were lost may allow identification of interesting genetic defects that could be involved in tumour expansion. Thus, sequential xenografts of colon tumours will provide a powerful model for further study of tumour clonality and for the identification of genetic profiles responsible for differential resistance to therapeutic treatments. Our data also suggest that tumour expansion can result from alterations in several distinct genetic pathways.

Allelic imbalance at loci containing FGFR, FGF, c-Met and HGF candidate genes in non-small cell lung cancer sub-types, implication for progression

Fibroblast growth factors (FGF), hepatocyte growth factor (HGF) and their receptors, FGFR and c-Met, are essential components of the regulatory networks between the epithelium and mesenchyme in embryonic lung, but their respective roles in tumour growth are not clear. We performed allelotyping at loci containing the candidate genes FGFR-1-2-3-4, FGF-1-2-7-10, c-Met and HGF in 36 non-small cell lung cancer (NSCLC) (20 squamous-cell carcinomas (SQC) and 16 adenocarcinomas (ADC)), by surrounding each locus with two microsatellites (MS), as close as possible to the genes of interest. Unexpectedly, SQC and ADC were frequently altered at all of these loci, and SQC showed more simultaneously altered loci. In ADC, alterations at the 15q13-22 locus (FGF7 candidate gene) were significantly more frequent. Thus, these loci showed different patterns of molecular alterations between SQC and ADC. Finally, alterations at loci containing FGFR and HGF candidate genes were inversely correlated to the lymph node status in SQC and ADC, respectively.

Genetic alterations in primary osteosarcoma from 54 children and adolescents by targeted allelotyping

At present, the only recognised prognostic factor for primary osteosarcoma is the histological response to preoperative chemotherapy. Our study was designed to identify new diagnostic markers that could eventually have a prognostic value. A total of 54 patients under 20 years of age with primary osteosarcomas were studied while under treatment by the French Society of Paediatric Oncology OS 94 protocol. Paired normal and biopsy samples were collected. In addition, surgical resection specimens, following preoperative chemotherapy, were obtained in 13 cases. After genomic DNA extraction, an allelotyping analysis targeting microsatellites linked to Rb and p53 genes, and 9p21, 7q31 and 5q21 regions was performed. In all, 94% of the samples at diagnosis showed allelic imbalance and the biopsies were highly rearranged except for the microsatellite targeting 7q31. The same panel was highly informative at surgical resection. Microsatellites investigating Rb, p53 and the 9p21 region were particularly altered without a significant correlation with prognosis. On the other hand, the alteration of the 7q31 locus at diagnosis was significantly correlated with a worse prognosis and a new frequently altered locus, 5q21, was described. In conclusion, this panel allowed us to characterise paediatric osteosarcomas. Correlation of prognosis with the altered 7q31 region could be a useful tool and further studies are required to confirm the importance of 5q21.

Modification of topoisomerase genes copy number in newly diagnosed childhood acute lymphoblastic leukemia

Topoisomerase genes were analyzed at both DNA and RNA levels in 25 cases of newly diagnosed childhood acute lymphoblastic leukemia (ALL). The results of molecular analysis were compared to risk group classification of children in order to identify molecular characteristics associated with response to therapy. At diagnosis, allelic imbalance at topo-isomerase IIalpha (TOP2A) gene locus was found in 75% of informative cases whereas topoisomerase I and IIbeta gene loci are altered in none or only one case, respectively. By semi-quantitative Polymerase chain reaction, we found a 2.5 to 8-fold TOP2A gene amplification in 72% of the children, which was correlated to gene overexpression in every case. These results show that TOP2A gene amplification is a frequent event in ALL at diagnosis. Interestingly, we also identified a small population of children that do not present TOP2A gene amplification or gene overexpression and who are significantly associated with very high risk classified patients showing glucocorticoid resistance. In conclusion, characterization of TOP2A gene status in childhood ALL at diagnosis provides useful complementary information for risk assessment.

Analysis of allelic imbalance in patients with colorectal cancer according to stage and presence of synchronous liver metastases

OBJECTIVE

To investigate the relationship between number and location of allelic imbalances (AI) and local tumor progression according to Astler-Coller classification.

SUMMARY BACKGROUND DATA

Spontaneous errors in DNA replication (i.e., allelic imbalance or microsatellite instability) have been suggested to play an important role in carcinomatous transformation as reflecting alterations of gene function.

METHODS

One hundred two consecutive patients with colorectal carcinoma undergoing surgical resection were included in this study. Patients were distributed according to the Astler-Coller classification as stages A (n = 7), B1 (n = 15), B2 (n = 24), C (n = 31), and D (n = 25). Fluorescent polymerase chain reaction was performed on frozen tumor, normal colon mucosa, and blood DNA at 35 microsatellite markers. Allelic imbalance frequency was compared with tumor staging.

RESULTS

The percentage of AI was significantly higher in stage D than in A/B1 and B2. In addition, the percentage of AI was significantly higher in 10 synchronous colorectal liver metastases than in stage A/B1 and B2 tumors. However, the allelotyping revealed a subgroup of A/B1 tumors with a high AI frequency. Statistical analysis showed that the presence of AI at microsatellites D1S305, D2S138, D3S1282, D17S790, and D22S928 presented a significantly positive correlation with stages.

CONCLUSION

The frequency of AI significantly correlates with tumor progression of colorectal cancer. Primary tumors with synchronous colorectal liver metastases showed a higher percentage of AI, suggesting that a frequency of AI greater than 35% with this selection of markers indicates a high risk of local progression and of development of metastases.

Evaluation of microsatellite analysis in urine sediment for diagnosis of bladder cancer

Alterations at microsatellite DNA markers in cells exfoliated in urine have been correlated to the presence of bladder cancer. To check the feasibility of such noninvasive analysis to routinely diagnose bladder cancers, we have developed a highly sensitive method using fluorescent PCR to search for DNA microsatellite alterations in urine sediment compared with a blood paired sample. One hundred eighty-three patients were included in our study. This population comprised 103 bladder cancers (64 pTa stages), the complement representing controls and other benign or malignant diseases. Results of the analysis at 17 loci in a blinded study were compared with cystoscopy and/or pathology. The high reproducibility of this technique and the analysis of 26 control patients allowed us to determine for each microsatellite a cutoff characterizing a significant allelic imbalance. For bladder cancer detection, the overall sensitivity of the test was 84%. Using this procedure, we identified alterations in 81%, 84%, 91%, and 100% of pTa, pT1, pT2, and >pT2 stages, respectively. This corresponds to 79%, 82%, and 96% sensitivity for grades I, II, and III, respectively. Interestingly, for routine purposes, we observed an overall sensitivity of 80% (76% for pTa stages) when only the eight most rearranged microsatellites were considered. In conclusion, the noninvasive feature combined with the rapidity of this fluorescent and highly sensitive technique for the detection of early stages provides us with a useful help for the diagnosis of bladder cancer.

Microsatellite instability and allelic imbalance in primary and secondary colorectal cancer

BACKGROUND

Several studies of colorectal cancer have shown an association between the number and type of genomic defects and the stage of disease. A subset of colorectal tumours are due to inactivation of DNA mismatch repair genes and these tumours exhibit microsatellite instability. The aim of the present study was to compare and contrast the genomic defects present in both the primary and metastatic stages of the disease using microsatellite probes.

METHODS

Modifications of the allelic profiles of 25 microsatellite regions were studied in a total of 85 colorectal tumours using fluorescent polymerase chain reaction (PCR) technology and subsequent direct analysis on an automatic sequencer. This approach was used because it allows the study of microsatellite instability and allelic imbalance. Stepwise logistic regression analysis was used to develop a model to predict whether the tumour was primary or secondary from the percentage of allelic imbalance. Subsequently, a group of 17 patients with primary colorectal tumours was analysed prospectively to test the proposed model.

RESULTS

Six of 39 primary tumours showed microsatellite instability compared to 0 of 29 liver metastases (P = 0.03). Primary tumours showed significantly less allelic imbalance than liver metastases (P < 0.001). Three probes (d18s53, d9s158 and d10s191) were selected for use in a model to classify a tumour as primary or secondary on the basis of the degree of allelic imbalance. When tested prospectively this model had a specificity of 82%.

CONCLUSIONS

The present study demonstrates the potential importance of using microsatellite probes both as a diagnostic tool and as a research technique to investigate the mechanisms of tumour progression. An important clinical finding is that none of the colorectal liver metastases showed microsatellite instability (0 of 29). This analysis also confirmed other work that has shown a direct relationship between the degree of allelic imbalance and the stage of disease.

Frequent factor II G20210A mutation in idiopathic portal vein thrombosis

BACKGROUND & AIMS

Despite extensive investigations of portal vein thrombosis, no underlying cause is identifiable in up to 30% of patients. A recently described mutation of the prothrombin gene at nucleotide position 20210 is associated with history of venous thrombosis and was assessed in this study.

METHODS

We compared the frequency of factor II G20210A and factor V G1691A (factor V Leiden) mutations in 10 patients with idiopathic portal vein thrombosis, 10 patients with nonidiopathic portal vein thrombosis, 60 patients with deep vein thrombosis of the legs, and 42 control subjects.

RESULTS

The frequency of factor II G20210A mutation was increased in patients with idiopathic portal vein thrombosis (40.0%; confidence interval, 3.1%-76.9%) compared with controls (4.8%; confidence interval, 0%-11.5%) or patients with nonidiopathic portal vein thrombosis or deep vein thrombosis (P = 0.0001). In contrast, the frequency of the factor V G1691A mutation was similar in subjects with portal vein thrombosis and in controls but was increased in patients with deep vein thrombosis (P = 0.0001).

CONCLUSIONS

The factor II G20210A mutation is frequent in patients with idiopathic portal vein thrombosis and should therefore be assessed under this circumstance.

Nuclear detection of cellular retinoic acid binding proteins I and II with new antibodies

Apart from the retinoic acid nuclear receptor family, there are two low molecular weight (15 kD) cellular retinoic acid binding proteins, named CRABPI and II. Mouse monoclonal and rabbit polyclonal antibodies were raised against these proteins by using as antigens either synthetic peptides corresponding to amino acid sequences unique to CRABPI or CRABPII, or purified CRABP proteins expressed in E. coli. Antibodies specific for mouse and/or human CRABPI and CRABPII were obtained and characterized by immunocytochemistry and immunoblotting. They allowed the detection not only of CRABPI but also of CRABPII in both nuclear and cytosolic extracts from transfected COS-1 cells, mouse embryos, and various cell lines.

Phosphorylation of activation functions AF-1 and AF-2 of RAR alpha and RAR gamma is indispensable for differentiation of F9 cells upon retinoic acid and cAMP treatment

The role of RAR alpha 1 and RAR gamma 2 AF-1 and AF-2 activation functions and of their phosphorylation was investigated during RA-induced primitive and parietal differentiation of F9 cells. We found that: (i) primitive endodermal differentiation requires RAR gamma 2, whereas parietal endodermal differentiation requires both RAR gamma 2 and RAR alpha 1, and in all cases AF-1 and AF-2 must synergize; (ii) primitive endodermal differentiation requires the proline-directed kinase site of RAR gamma 2-AF-1, whereas parietal endodermal differentiation additionally requires that of RAR alpha 1-AF-1; (iii) the cAMP-induced parietal endodermal differentiation also requires the protein kinase A site of RAR alpha-AF-2, but not that of RAR gamma; and (iv) the AF-1-AF-2 synergism and AF-1 phosphorylation site requirements for RA-responsive gene induction are promoter context-dependent. Thus, AF-1 and AF-2 of distinct RARs exert specific cellular and molecular functions in a cell-autonomous system mimicking physiological situations, and their phosphorylation by kinases belonging to two main signalling pathways is required to enable RARs to transduce the RA signal during F9 cell differentiation.

Distinct conformations of vitamin D receptor/retinoid X receptor-alpha heterodimers are specified by dinucleotide differences in the vitamin D-responsive elements of the osteocalcin and osteopontin genes

The 1 alpha,25-dihydroxyvitamin D3 (VD3)-dependent stimulation of osteocalcin (OC) and osteopontin (OP) gene transcription in bone tissue is mediated by interactions of trans-activating factors with distinct VD3-responsive elements (VDREs). Sequence variation between the OC- and OP-VDRE steroid hormone half-elements provides the potential for recognition by distinct hormone receptor homo- and heterodimers. However, the exact composition of endogenous VD3- induced complexes recognizing the OC- and OP-VDREs in osteoblasts has not been definitively established. To determine the identity of these complexes, we performed gel shift immunoassays with nuclear proteins from ROS 17/ 2.8 osteoblastic cells using a panel of monoclonal antibodies. We show that VD3- inducible complexes interacting with the OC- and OP-VDREs represent two distinct heterodimeric complexes, each composed of the vitamin D receptor (VDR) and the retinoid X receptor-alpha (RXR). The OC- and OP-VDR/RXR alpha heterodimers are immunoreactive with RXR antibodies and several antibodies directed against the ligand-binding domain of the VDR. However, while the OC-VDRE complex is also efficiently recognized by specific monoclonal antibodies contacting epitopes in or near the VDR DNA-binding domain (DBD) (between amino acids 57-164), the OP-VDRE complex is not efficiently recognized by these antibodies. By systematically introducing a series of point-mutations in the OC-VDRE, we find that two internal nucleotides of the proximal OC-VDRE half-site (nucleotide -449 and -448; 5'-AGGACA) determine differences in VDR immunoreactivity. These results are consistent with the well established polarity of RXR heterodimer binding to bipartite hormone response elements, with the VDR recognizing the 3'-half-element. Furthermore, our data suggest that the DBD of the VDR adopts different protein conformations when contacting distinct VDREs. Distinctions between the OC- and OP-VDR/RXR alpha complexes may reflect specialized requirements for VD3 regulation of OC and OP gene expression in response to physiological cues mediating osteoblast differentiation.

Differential changes of retinoid-X-receptor (RXR alpha) and its RAR alpha and PML-RAR alpha partners induced by retinoic acid and cAMP distinguish maturation sensitive and resistant t(15;17) promyelocytic leukemia NB4 cells

The expression of retinoid receptors (RXRalpha, RARalpha and the chimeric form PML-RARalpha) was analysed both at the mRNA and protein level in the maturation sensitive NB4 and resistant NB4-R1 cell lines of t(15;17) promyelocytic leukemia (APL). All-trans RA and cAMP which show synergistic activity in inducing maturation of NB4 cells and maturation triggering of the RA 'primed' NB4-R1 resistant cells, distinctly modulate RXRalpha, RARalpha and PML-RARalpha mRNA. In the NB4 and NB4-R1 cells, RXRalpha mRNA was downregulated by RA, but only in RA-primed NB4-R1 cells a release from RXRalpha mRNA downregulation was obtained by cAMP treatment. RXRalpha protein (53 kDa) was decreased to the western-blot detection limit (97.5%) by RA in NB4 cells, but in NB4-R1 cells although it was frankly decreased (85%), the signal for RXRalpha protein remained very significant. More importantly, while cAMP slightly upregulated RXRalpha protein in RA-treated NB4 cells, it caused an increase of RXRalpha protein in RA-treated NB4-R1 cells bringing RXRalpha to the initial control level. RXRalpha partners in heterodimers (PML-RARalpha, RARalpha) were also analysed. In contrast to RXRalpha, RARalpha and PML-RARalpha mRNA were not modulated by RA and/or cAMP, while significant changes were observed at the protein levels. A putatively phosphorylated form of RARalpha (52 kDa) decreased during maturation of NB4 cells, but was unchanged in resistant NB4-R1 cells. Conversely, while PML-RARalpha remained stable during RA-induced NB4 maturation, RA treatment which failed to induce maturation of NB4-R1 cells significantly down-regulated the chimeric receptor (120 kDa). These differences most likely results from translational and post-translational regulation. This work reveals complex pattern of subtle changes at the protein level distinguishing RA-sensitive and RA-resistant cells. Our data show that the RA-cAMP synergistic effect on NB4 cell maturation and cooperation in triggering maturation of RA-primed NB4-R1 cells operate changes in the RXR/PML-RARalpha ratio which are both favouring RXRalpha. In both cell lines, variations of PML-RARalpha and RXRalpha may result in a decrease in the formation of the PML-RARalpha/RXRalpha heterodimers which are supposed involved in the block of maturation. This may prove crucial to embark cells on maturation.

Reexpression of retinoic acid receptor (RAR) gamma or overexpression of RAR alpha or RAR beta in RAR gamma-null F9 cells reveals a partial functional redundancy between the three RAR types

Disruption of retinoic acid receptor (RAR) gamma in F9 embryonal carcinoma cells leads to aberrent differentiation and reduced activation of expression of several all-trans-retinoic acid (RA)-induced genes. We have analyzed the expression of several additional RA-responsive genes in RAR alpha- and RAR gamma-null F9 cells. The RA-induced activation of Cdx1, Gap43, Stra4, and Stra6 was specifically impaired in RAR gamma-null cells, supporting the idea that each RAR may regulate distinct subsets of target genes. To further investigate the role of RAR gamma in F9 cell differentiation, "rescue" cell lines reexpressing RAR gamma 2 or overexpressing either RAR alpha 1 or RAR beta 2 were established in RAR gamma-null cells. Reexpression of RAR gamma or overexpression of RAR alpha restored both target-gene activation and the differentiation potential. In contrast, over-expression of RAR beta only poorly restored differentiation, although it could replace RAR gamma for the activation of target genes. Functional redundancy between the various RARs is discussed.

Characterization of nuclear retinoic acid binding activity in sensitive leukemic cell lines: cell specific uptake of ATRA and RAR alpha protein modulation

The diverse effects of all-trans retinoic acid (ATRA) on growth, differentiation and homeostasis of vertebrate organisms are mediated by three distinct isoforms of retinoic acid receptors (RARs). Although it is not known to what extent each RAR contributes to the different effects of ATRA, several studies have demonstrated that ATRA induced granulocytic differentiation in human myeloid leukemic cell lines is mediated by RAR alpha. In this study, we investigated ATRA binding affinity of the endogenous nuclear receptors of HL-60 and NB4 leukemic cells. Scatchard plot analysis yielded an apparent dissociation constant of 5 +/- 0.3 nM and 1400 +/- 80 receptor sites per cell in HL-60 cells, whereas the NB4 promyelocytic leukemic cell line showed a lower affinity (8.5 +/- 0.5 nM and 900 +/- 30 receptor sites per cell). Modulation of RAR alpha protein (5 fold excess) was found in NB4 cells after 24 hours ATRA exposure, whereas HL-60 cells required a 72-hour culture period to weakly increase the RAR alpha protein level. These data were closely related to the ATRA intracellular concentration and kinetics of terminal differentiation of the cells.

Phosphorylation of the retinoic acid receptor-alpha by protein kinase A

The phosphorylation of retinoic acid receptor-alpha 1 (RAR alpha 1) by PKA was investigated both in vitro and in vivo. We show that bacterially expressed RAR alpha 1 is phosphorylated in vitro by protein kinase A (PKA) at the unique serine residue 369 located in the C-terminal end of the E region. We also show that RAR alpha 1 overexpressed in COS-1 cells is phosphorylated on multiple serine residues and that phosphorylation at serine 369 occurs only when COS-1 cells are cotransfected with PKA or treated with forskolin. RAR alpha 1 mutants were constructed in which serine 369 was replaced by an alanine (S369A) or a glutamic acid (S369E) residue. Comparison of the tryptic phosphopeptide patterns of wild type and mutated RAR alpha 1 overexpressed in COS-1 cells allowed us to confirm that serine 369 is the unique phosphorylation site for PKA in cultured cells. The DNA-binding efficiency of RAR alpha/retinoid X receptor-alpha (RXR alpha) heterodimers was enhanced in vitro by the S369E mutation. However, in transfected RAC65 cells, the same S369E mutation did not affect the ligand-dependent transcriptional activation by RAR alpha 1 of reporter genes containing a retinoic acid (RA)-response element. In contrast, the S369A mutation slightly decreased both DNA binding and the efficiency of PKA to enhance RA-induced transactivation by RAR alpha 1. Finally, we show that endogenous RAR alpha is also phosphorylated in vivo at serine 369 in forskolin-treated F9 cells, supporting the idea that phosphorylation of RARs at this site is involved in the modulation of the RA-induced differentiation of F9 cells by (Bu)2cAMP.

Protein phosphatases 1 and 2A regulate the transcriptional and DNA binding activities of retinoic acid receptors

To determine which factors may regulate the DNA binding and transcriptional properties of retinoic acid receptors (RARs and RXRs), we investigated the sensitivity of reporter genes bearing various retinoic acid response elements (RAREs) to protein phosphatases (PPases) inhibition. PPases inhibition by okadaic acid led to an increase of the reporter genes activity in a RARE-dependent and ligand-independent manner and was dependent on the type of response element used. Overexpression of protein phosphatases 2A and 1 (PP2A and PP1) decreased the inducibility of the reporter genes tested. Nuclear extracts from okadaic acid-treated COS cells displayed an 2-5-fold increased level of receptor binding to RAREs in vitro, suggesting that PPases inhibition increased the DNA binding activity of retinoid receptors. Treatment of receptors extracted from COS cells by alkaline phosphatase and partially purified PP1 and PP2A decreased their DNA binding activity, but heterodimers bound to DNA were not sensitive to phosphatase treatment. Reconstitution experiments showed that phosphorylation of both receptors increased the DNA binding activity of RXR/RAR heterodimers. Taken together, these data show that the modulation of the phosphorylation state of RARs and RXRs represents an other level of regulation of the retinoid signaling pathway.

Characterization of retinoic acid- and cell-dependent sequences which regulate zif268 gene expression in osteoblastic cells

We have previously shown that retinoic acid (RA) induces differentiation in an osteoblastic cell line derived from embryonic rat calvaria and that RA has selective effects on zif268 gene expression in these preosteoblastic cells,distinct from those in more mature osteoblasts. In this study we demonstrate that the RA-dependent transcriptional increase in zif268 gene expression is mediated by the interaction of RA receptors (RARs) with a 17 base pair sequence in the zif268 promoter containing a single half-site motif (GTTCA), identical to each of the direct repeats seen in the RAR beta 2 gene. The sequence appears relatively RA-specific, since the zif268 RA-responsive element is not activated by 1,25-dihydroxyvitamin D3 or thyroid hormone (T3). However, cotransfection of RAR expression vectors and an SV-40 promoter chloramphenicol acetyltransferase (CAT) construct containing the single zif268 RA-responsive motif into CV-1 cells demonstrates that the alpha-, beta-, and gamma-RARs transactivate through this element. Extensive mutagenesis of the zif268 promoter region containing the RA response element (RARE) motif confirms that the transactivation and nuclear protein binding activity of this region requires only the half-site motif. The direct involvement of RAR in this DNA-protein interaction has been demonstrated by competitive gel retardation analysis using consensus RAREs and super-shifting of the DNA-protein complex with mouse alpha- or gamma-RAR monoclonal antibodies. In addition, we found that cell-specific suppression of RA-stimulated zif268 gene expression can be attributed to a 29 base pair nucleotide sequence, located downstream of the RA-responsive region in the zif268 gene. This sequence appears to be bound specifically by nuclear protein(s) from several cell types, including osteoblasts. The presence of this sequence in cis to the zif268 RARE or the consensus beta RARE completely blocks the RA-responsiveness of the zif268 gene in differentiated osteoblasts. These data extend the broad spectrum of RA-responsive sequences necessary for DNA binding and transactivation to include regulation via single RARE half-site motifs and suggest that the lack of RA responsiveness in differentiated osteoblasts may be mediated by cell-specific suppression of gene expression.

Retinoic acid receptor beta 2 (RAR beta 2) null mutant mice appear normal

Vertebrates are highly sensitive to both retinoic acid (RA) deficiency and excess. The RA signal is thought to be transduced by nuclear receptors (the RAR and RXR families) which activate the expression of target genes via cis-acting transcriptional enhancer elements. Each of the three RAR genes, RAR alpha, RAR beta, and RAR gamma, gives rise to several isoforms by differential usage of two promoters and alternative splicing. RAR beta 2 is the most abundant of the four RAR beta isoforms, and its transcription is spatially and temporally restricted in developing embryos, suggesting that it might perform specific functions. Furthermore, RAR beta 2 expression can be induced via a retinoic acid response element located in its promoter region. This RA effect is particularly interesting since under conditions of RA excess, RAR beta 2 promoter activity and transcript accumulation are induced in regions of developing embryos in which malformations subsequently appear, such as the craniofacial region, the hindbrain, and the limbs. These findings have led to the suggestion that the RAR beta 2 isoform might mediate some of the teratogenic effects of RA. In this study, we have eliminated RAR beta 2 expression by targeted gene disruption. RAR beta 2 null mutants exhibit an apparently normal phenotype, indicating that other RARs must compensate for RAR beta 2 sufficiently well to allow normal prenatal and postnatal development to proceed. By challenging RAR beta 2 null embryos with teratogenic doses of RA, we have also directly addressed the question of whether RAR beta 2 is required for mediating RA-induced malformations.

Detection of retinoid X receptors using specific monoclonal and polyclonal antibodies

Because of the growing importance of the Retinoid X Receptors (RXR alpha, beta and gamma) in the retinoid acid signalling pathway, we have prepared polyclonal and monoclonal antibodies directed against these proteins. For this purpose, either the whole mouse RXR alpha protein expressed in E.Coli, or synthetic peptides corresponding to amino acid sequences common to all RXRs or unique to RXR alpha, beta or gamma, were used as antigens. Antibodies recognizing either all three RXR types (alpha, beta and gamma) or specific for each RXR type were obtained. The antibodies were characterized by immunocytochemistry, immunoblotting, immunoprecipitation and electromobility shift assay (EMSA). These antibodies allowed us to detect the presence of RXR alpha proteins in mouse embryos and in mouse embryonal carcinoma cells (F9 and P19 cell lines) by immunoblotting, immunoprecipitation and EMSA whereas RXR beta could be detected only by EMSA and RXR gamma could not be detected by any of these techniques.

Immunological identification and functional quantitation of retinoic acid and retinoid X receptor proteins in human skin

We have determined protein levels of total and individual nuclear retinoic acid (RAR-alpha, -beta, -gamma) and retinoid X (RXR-alpha, -beta, -gamma) receptors by ligand binding, Western analysis, and gel shift assays, in adult human skin, a major retinoid-responsive tissue. Total RARs and RXRs, measured by direct binding of specific ligands, were 0.24 +/- 0.01 fmol/micrograms (n = 13) and 1.26 +/- 0.08 fmol/micrograms (n = 7), respectively. These values calculated on an average per cell basis were 1790 RARs/cell and 9400 RXRs/cell. Similar results were obtained with competitive ligand binding assays. RAR-alpha, -beta, and -gamma were each specifically immunoprecipitated, and their levels determined by ligand binding assays of supernatants and Western analysis of precipitates. RAR-gamma was the most abundant, representing 87% of RAR protein. The remaining 12-14% of RAR protein was RAR-alpha. No RAR-beta was detected. Similar immunoprecipitation studies revealed that RXR-alpha represented 90% of RXR protein expressed in human skin. No RXR-beta or RXR-gamma proteins were detected by Western blot. Supershift gel retardation with antibodies to RARs detected probe-RAR-alpha and probe-RAR-gamma complexes in a 1 to 4 ratio. No probe-RAR-beta complex was detected. With antibodies to both RAR-gamma and RXR, a double supershifted complex was formed, indicating that RAR-gamma/RXR heterodimers bound to the probe. These data demonstrate 1) protein levels of RXRs are five times greater than RARs, 2) relative protein levels of RAR and RXR family members are compatible with their previously described relative mRNA levels, and 3) RXR-alpha/RAR-gamma heterodimers are the major retinoid receptors that have the potential to regulate transcription of target genes, in adult human skin.

High postnatal lethality and testis degeneration in retinoic acid receptor alpha mutant mice

Retinoic acid (RA) plays a critical role in normal development, growth, and maintenance of certain tissues. The action of RA is thought to be mediated in part by the three nuclear receptors (RAR alpha, -beta, and -gamma), each of which is expressed as multiple isoforms. To investigate the function of the RAR alpha gene, we have disrupted, in the mouse, the whole gene or the isoform RAR alpha 1. Although RAR alpha 1 is the predominant isoform and is highly conserved among vertebrates, RAR alpha 1-null mice appeared normal. However, targeted disruption of the whole RAR alpha gene resulted in early postnatal lethality and testis degeneration. These results, showing that RAR alpha is indeed involved in the transduction of the RA signal, also suggest an unexpected genetic redundancy.

Retinoic acid receptor-beta: immunodetection and phosphorylation on tyrosine residues

Polyclonal (RP) and monoclonal (Ab) antibodies were raised against synthetic peptides (or fusion proteins) corresponding to amino acid sequences unique to human and mouse retinoic acid receptor-beta (RAR beta) isoforms. Antibodies directed against the A2 region [Ab6 beta 2(A2), Ab7 beta 2(A2), and RP beta 2(A2)], the D2 region [RP beta(D2)], or the F region [Ab8 beta(F)2, RP beta(F)1, and RP beta(F)2] were selected. The monoclonal and polyclonal antibodies directed against the D2 and F regions specifically immunoprecipitated and recognized by Western blotting all human and mouse RAR beta isoforms (mRAR beta 1, -beta 2, -beta 3, and -beta 4), produced in COS-1 cells transfected with expression vectors containing the corresponding RAR beta cDNA. Furthermore, in gel retardation assays, the monoclonal antibodies supershifted RAR beta protein-RA response element oligonucleotide complexes. Antibodies directed against the A2 region were specific for the RAR beta 2 isoform. The above antibodies allowed us to detect the presence of mRAR beta 2 proteins in mouse embryos and to show that their presence in embryonal carcinoma cells (F9 and P19 cell lines) is dependent upon RA treatment. The antibodies were also used to demonstrate that RAR beta proteins produced by transfection in COS-1 cells are phosphorylated. RAR beta 2 phosphorylation was not affected by RA treatment, whereas the phosphorylation of RAR beta 1 and RAR beta 3 isoforms was greatly enhanced by RA. We also show that, in contrast to RAR alpha 1 and RAR gamma 1, RAR beta 2 proteins contain phosphotyrosine residues and are only weakly phosphorylated in vitro by cAMP-dependent protein kinase. These results support our previous proposal that the various receptors have distinct functions in the RA-signaling pathway.

Immunodetection of multiple species of retinoic acid receptor alpha: evidence for phosphorylation

Polyclonal and monoclonal antibodies were raised against synthetic peptides (or fusion protein) corresponding to cDNA-deduced amino acid sequences unique to the human and mouse retinoic acid (RA) receptor alpha 1 (hRAR-alpha 1 and mRAR-alpha 1, respectively). Two rabbit polyclonal antibodies directed against either the F region fused to DHFR [RP alpha (F)] or the D2 region [RP alpha (D2)] were selected. Using either immunocytochemistry, Western blotting analysis, or immunoprecipitation, they were found to be specific for human and mouse RAR-alpha 1 proteins produced by COS-1 cells transiently transfected with vectors expressing the RAR-alpha 1 cDNA. Three mouse monoclonal antibodies directed against either the F region [(Ab9 alpha (F) and Ab12 alpha (F)] or the A1 region [Ab10 alpha 1(A1)] recognized transiently expressed human and mouse RAR-alpha 1 proteins, when either immunocytochemistry or immunoprecipitation was used. In addition, Ab9 alpha (F) and Ab12 alpha (F), but not Ab10 alpha 1(A1), revealed the RAR-alpha 1 proteins by Western blotting analysis. Ab9 alpha (F) was also able to "supershift" RAR-alpha 1 protein-RARE oligonucleotide probe complexes in gel retardation assays. All these antibodies recognized also the transiently expressed mRAR-alpha 2 isoform, with the exception of Ab10 alpha 1 (A1), which is specific for the A1 region of RAR-alpha 1. These antibodies have enabled us to detect the presence of mRAR-alpha as multiple species in mouse embryo and adult tissue extracts as well as in embryonal carcinoma (EC) cells. Moreover, we found that one of these species (51 kDa) was phosphorylated in EC cells. This phosphorylation was not affected by RA treatment, but appeared to be dependent on the differentiation state of the EC cells.

Characterization of a retinoic acid responsive element isolated by whole genome PCR

We have used whole PCR in an attempt to isolate novel retinoic acid (RA) responsive genes. We cloned several small genomic fragments from total human DNA containing putative retinoic acid responsive elements (RAREs) selected by direct binding to the retinoic acid receptor alpha (RAR alpha). We report here that an oligonucleotide containing a sequence from one of the cloned human DNA fragments, and referred to as alpha 1, functions as an authentic RARE. It is shown that both RAR alpha and RAR beta produced in Cos cells as well as in vitro translated RAR alpha bind directly and sequence-specifically to the alpha 1RARE. By mutational analysis it is demonstrated that the alpha 1RARE consists of an imperfect direct repeat of the estrogen- and thyroid hormone-related AGGTCA half-site motif separated by a 5 bp spacer. The orientation and spacing of the half-site repeats are shown to play a critical role in RAR recognition. When cloned upstream of a TK-Luc reporter, the alpha 1RARE is shown to confer responsiveness to RA in an orientation-independent fashion in F9 and CV-1 cells. The magnitude of the RA response mediated by the alpha 1RARE differed in these cell lines.

Structure, localization and transcriptional properties of two classes of retinoic acid receptor alpha fusion proteins in acute promyelocytic leukemia (APL): structural similarities with a new family of oncoproteins

Acute promyelocytic leukemia (APL) is due to a chromosomal t(15;17) translocation which involves a novel human gene, Myl, (also named PML) and the retinoic acid (RA) receptor alpha (RAR-alpha) gene. We report here the characterization of Myl and of the reciprocal MylRAR (PMLRAR) and RARMyl (RARPML) fusion transcripts which are found in two classes of APL patients. Myl displays similarities with a new family of proteins of which some members are fused to protooncogenes in the transforming proteins RFP-ret and T18. The speckled nuclear localization of Myl, as well as its sequence homology with the 52 kDa component of the RO/SSA ribonucleoprotein particle, suggest that Myl may be present in a ribonucleoprotein complex. In contrast to both Myl and RAR-alpha whose localization is essentially nuclear in the presence or absence of RA, MylRAR which is largely cytoplasmic in the absence of RA appears to be translocated to the nucleus in the presence of RA. Myl and MylRAR can associate in vitro and this association is mediated by a coiled coil in the Myl sequence. In vivo this association results in a colocalization of Myl and MylRAR which is identical to that of MylRAR alone. Studies of activation of transcription from the promoters of several RA target genes indicate that MylRARs have altered transcription activation properties when compared with RAR-alpha. Most notably, MylRAR represses markedly the activity of some RA target promoters in the absence of RA. Western blot analyses of patient samples show that MylRAR is expressed to a much higher level than wild type RAR-alpha originating from the normal allele. Taken together, these results suggest that MylRAR may interfere in a dominant manner with both Myl and RAR functions.

Retinoic acid receptor gamma: specific immunodetection and phosphorylation

Synthetic peptides corresponding to cDNA-deduced amino acid sequences unique to the human and mouse retinoic acid receptor gamma 1 (hRAR-gamma 1 and mRAR-gamma 1, respectively) were used to generate anti-RAR-gamma 1 antibodies. Four mAbs were selected, which were directed against peptides found in region A1 (Ab1 gamma (A1)), region F (Ab2 gamma (mF) and Ab4 gamma (hF)) and region D2 (Ab5 gamma (D2)). These antibodies specifically immunoprecipitated and recognized by Western blotting RAR-gamma 1 proteins in COS-1 cells transfected with expression vectors containing the RAR-gamma 1 cDNAs. They all reacted with both human and mouse RAR-gamma 1 proteins, except Ab4 gamma (hF) that was specific for hRAR-gamma 1. Rabbit polyclonal antibodies, directed against a peptide from the mRAR-gamma 1 F region were also obtained (RP gamma (mF)) and found to be specific for mouse RAR-gamma 1 protein. Furthermore, in gel retardation/shift assays the antibodies specifically retarded the migration of complexes obtained with a RA response element (RARE). Antibodies raised against regions D2 and F also recognized the RAR-gamma 2 isoform which differs from RAR-gamma 1 only in the A region. On the other hand, antibodies directed against the A1 region of RAR-gamma 1 (Ab1 gamma (A1)) only reacted with the RAR-gamma 1 protein. The antibodies characterized here allowed us to detect the presence of mRAR-gamma 1 and gamma 2 isoforms in mouse embryos and F9 embryonal carcinoma cells nuclear extracts. They were also used to demonstrate that the mRAR-gamma 1 protein can be phosphorylated and that the phosphorylation occurs mainly in the NH2-terminal A/B region.

The late retinoic acid induction of laminin B1 gene transcription involves RAR binding to the responsive element

Transcription of the murine laminin B1 (LB1) gene is induced by retinoic acid (RA), but responds only 24-28 h after RA treatment in F9 EC cells. Here we have shown by gel retardation assay that all three retinoic acid receptors (RARs) alpha, beta and gamma expressed in Cos cells can bind directly to the previously characterized retinoic acid response element (RARE) of the LB1 promoter, albeit with a weaker affinity than to the RAR-beta gene RARE. Three stereo-aligned TGACC-like motifs are crucial for this binding. Interestingly, the capacity of RAR-alpha, -beta and -gamma to bind the LB1 RARE appears to be differentially modulated by factor(s) present in HeLa cells infected with RAR-expressing vaccinia virus vectors. Analyses of LB1 RARE mutants provide a strong correlation between RA-inducibility in vivo and efficiency of RAR binding in vitro. Thus, RARs can participate directly in transcriptional induction of the LB1 gene, even though this induction is cycloheximide sensitive and RARs are present in F9 cells prior to RA addition.

Activation of the ovalbumin gene by the estrogen receptor involves the fos-jun complex

The proximal region of the ovalbumin gene promoter contains a half-palindromic estrogen-responsive element (ERE) that mediates cell-specific trans-activation by the estrogen receptor (ER). We show that the ovalbumin ERE binds a ubiquitous nucleoprotein complex containing oncoproteins c-Fos and c-Jun. Mutations altering the estrogen inducibility of the promoter prevent the complex formation, which is, however, found in the presence and absence of ER and estradiol. Mutagenesis indicates that the sequence 5'-TGGGTCA-3', containing the half-palindromic ERE, is responsible for induction by phorbol esters of the ovalbumin promoter and is a target for c-fos and c-jun trans-activation. Transfection experiments reveal that c-fos, c-jun, and ER coactivate the ovalbumin promoter. Direct ER interaction with the target sequence is not required, since an ER deleted for its DNA binding domain is functional in the coactivation with c-fos and c-jun. Our data indicate a convergence of hormonal induction and activation of signal transduction pathways at the transcriptional level.

Isolation, partial purification and characterization of nuclear retinoic acid receptors from chick skin

Nuclear receptors (RARs) for retinoic acid (RA) are considered to be the ultimate mediators of the action of RA in the control of cell differentiation and inhibition of tumorigenesis. We have isolated and partially purified and characterized RAR from a RA-responsive tissue, chick embryo skin. The purification steps included Affi-Gel blue chromatography, ultrafiltration, size exclusion chromatography, and preparative isoelectric focusing. The electrofocusing of RAR-[3H]RA complex in ampholines (pH 3-10) revealed that the receptors have an isoelectric pH of 7.5. Whereas pronase-digested the RAR-[3H]RA complex completely, DNase showed 20-35% and RNase showed negligible digestive action on the complex. The ligand binding to RAR was completely inhibited by a mercury compound. RAR-alpha- and RAR-beta-specific antibodies, on Western blot analysis, immunoreacted with a protein having a molecular weight of 50,000, presumably RAR. Binding affinity studies revealed that biologically active analogs of RA with a free COOH group (e.g., 13-cis-RA, RO-13-7410, Ch 55, and Am 80) showed, like RA, high binding affinity for RAR, whereas biologically ineffective analogs of RA (e.g., furyl and pyridyl) were poor binders. Other groups of retinoids, in which the COOH group was either lacking or blocked, did not bind to RAR whether or not they were biologically active.

The retinoic acid receptors alpha and beta are expressed in the human promyelocytic leukemia cell line HL-60

The human promyelocytic leukemia cell line HL-60 can be induced to differentiate into granulocytes upon exposure to retinoids. Previously we have shown that extracts of undifferentiated HL-60 cells possess a specific retinoid-binding activity (RSBP-1) corresponding to an approximate 95 kilodalton (kDa) protein as determined by size-exclusion chromatography. We now extend these observations to reveal a second approximate 95 kDa retinoic acid-binding component (RSBP-2), which is separable from RSBP-1 using anion exchange chromatography. We further show that the chromatographic properties of RSBP-1 and RSBP-2 are identical to those found for the retinoid-binding activities present in extracts of HeLa cells transfected with the human retinoic acid receptor (RAR) expression vectors RAR-beta phi and RAR-alpha phi, respectively. Moreover, an antiserum preparation directed against RAR-beta selectively immunoprecipitated both the retinoid-binding activity in extracts of HeLa cells transfected with RAR-beta phi and that corresponding to RSBP-1 in HL-60 cell extracts. Similarly, an antiserum preparation directed against RAR-alpha immunoprecipitated the retinoid-binding activity in extracts from RAR-alpha phi transfected HeLa cell as well as that corresponding to RSBP-2 in HL-60 cell extracts. Using these antisera, Western blot analyses of extracts from HL-60 cells, and from HeLa cells transfected with either RAR-alpha phi or RAR-beta phi, confirmed that RSBP-2 and RSBP-1 are identical to RAR-alpha and RAR-beta, respectively. However, RAR-alpha, RAR-beta, RSBP-1, and RSBP-2 appeared as an approximate 51 kDa species in sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis in contrast with an apparent approximate 95 k mol wt as estimated from size-exclusion chromatography in the presence of 0.6 M KCl.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies specific to the retinoic acid human nuclear receptors alpha and beta

Two cDNAs encoding two human receptors for retinoic acid (RA), RAR-alpha and RAR-beta, have been characterized recently. Synthetic peptides corresponding to the cDNA-deduced amino acid sequences unique to RAR-alpha and RAR-beta were used to generate anti-RAR-alpha antiserum (SP171) and anti-RAR-beta antisera (SP172 and SP248). The specificity of these antisera was confirmed both by immunocytochemical detection of these receptors in COS-1 cells transfected with RAR-alpha and RAR-beta expression vectors and by immunoblot analyses performed with whole extracts of these cells. We also demonstrate that these antisera recognize RAR-alpha and RAR-beta endogenously expressed in the RA-responsive human promyelocytic leukemia cell line HL-60.

Cell-specific activity of a GGTCA half-palindromic oestrogen-responsive element in the chicken ovalbumin gene promoter

Using a transient co-transfection system we have identified a functional oestrogen responsive element (ERE) in the near vicinity of the TATA box of the chicken ovalbumin gene promoter. Oestrogen induced activation of transcription was observed only in chicken embryo fibroblast cells, and not in human HeLa cells, suggesting the existence of a cell-specific transcription factor(s) that is necessary for the hormonal response. By 5'-deletion mapping and site-directed mutagenesis, a sequence encompassing the more proximal of two GGTCA half-palindromic motifs was identified as a functional ovalbumin gene ERE. Both motifs correspond to oestrogen receptor binding sites in vitro as revealed by DNase I footprinting. Optimal response to the hormonal stimulus apparently requires stereoalignment of the ERE and the TATA box.

The N-terminal region of the chicken progesterone receptor specifies target gene activation

Steroid hormone receptors belong to a family of nuclear receptors that trigger transcriptional activation of target genes by specific binding to DNA recognition sequences, usually located in the 5'-flanking region of the target gene. Nuclear receptors appear to be segmented proteins and extensive structure-function analyses have attempted to elucidate the functional significance of individual segments. Two of these regions have been defined as the domains responsible for recognition of responsive elements of target genes (region C) and hormone binding (region E) (refs 2-7). But the functional significance of the N-terminal region (A/B), which diverges extensively even for a given receptor between different species, has remained obscure. We have previously cloned, expressed and analysed the chicken progesterone receptor (cPR) (ref. 8). This receptor and its human homologue from T47D breast cancer cells are unique among the steroid hormone receptors in that two forms, A and B, are present in equal amounts in cytosolic extracts, the latter having the higher molecular weight. For the chicken progesterone receptor, we have presented evidence suggesting that the cPR form A corresponds to an N-terminally truncated form of B (ref. 8). Here we report on the functional difference between the forms A and B in the transcriptional activation of two target genes.

Cell-specificity of the chicken ovalbumin and conalbumin promoters

A series of recombinant plasmids containing increasing lengths of the 5'-flanking promoter sequences of the chicken conalbumin and ovalbumin genes fused to the sequences coding for the SV40 T-antigen have been constructed. These recombinants were introduced into a variety of established cell lines and primary cultured cells by nuclear microinjection. Promoter activity was estimated by monitoring T-antigen synthesis by indirect immunofluorescence. We show that the microinjected ovalbumin and conalbumin promoter regions do not function in chicken fibroblasts, kidney cells and in a variety of non-chicken cells, irrespective of the presence of steroid hormone receptors. In contrast, these promoter regions are active in primary cultured chicken embryonic hepatocytes and oviduct tubular gland cells, suggesting the presence of cell-specific transcription factors in these cells. Unexpectedly, promoter sequences close to the TATA boxes of both the ovalbumin and conalbumin genes are sufficient to confer cell-specific expression. Most of the controls exerted on the ovalbumin and conalbumin promoters in the whole animal appear to be reproduced in vitro by nuclear microinjection of the chimeric genes into the primary cultured cells. However, the microinjected ovalbumin promoter is active in embryonic hepatocytes and thus escapes the regulation imposed on the corresponding inactive endogenous gene.

The chicken ovalbumin promoter is under negative control which is relieved by steroid hormones

Steroid hormone regulation of activity of the chicken ovalbumin promoter was studied by microinjection of chimeric genes into the nuclei of primary cultured oviduct tubular gland cells. The chimeric genes contained increasing lengths of ovalbumin gene 5'-flanking sequences fused to the sequence coding for the SV40 T-antigen. Promoter activity was estimated by monitoring synthesis of T-antigen. The activity of the ovalbumin promoter is cell-specifically repressed in these oviduct cells and the repression is relieved upon addition of steroid hormones. The -132 to -425 region of the ovalbumin promoter which is responsible for this negative regulation behaves as an independent functional unit containing the regulatory elements necessary for both repression (in the presence of steroid hormone antagonists) and induced derepression (in the presence of steroid hormones) of linked heterologous promoters.

Sequences upstream from the T-A-T-A box are required in vivo and in vitro for efficient transcription from the adenovirus serotype 2 major late promoter

We show that sequences located upstream from the T-A-T-A box, between positions -97 and -34, are necessary for efficient in vivo transcription from the adenovirus serotype 2 major late promoter. The effect of these upstream sequences was also investigated in vitro using a whole cell or an S100 extract and circular or linear templates. With the whole cell extract, the in vivo effect of the upstream sequences was reproduced in vitro. With the S100 extract, some effect of the upstream sequences was observed with circular, but not with linear, templates.

The SV40 72 base repair repeat has a striking effect on gene expression both in SV40 and other chimeric recombinants

By introduction of recombinant plasmids into monkey CV1 cells, we have unambiguously demonstrated that sequences entirely within the 72 bp repeat, which is located upstream of the SV40 early region, are crucial for T-antigen expression in vivo. We have also shown that a DNA fragment containing the 72 bp repeat, inserted directly before chicken conalbumin or adenovirus-2 major late promoter sequences in chimeric plasmids where these promoters replace that of the SV40 early genes, caused a dramatic increase in the expression of T-antigen in vivo. This effect was independent of the orientation of the 72 bp repeat, but was sensitive to its location within the plasmid, when the 72 bp repeat was separated from the promoter sequences, T-antigen expression was reduced. Insertion of the 72 bp repeat into equivalent plasmids containing no known eukaryotic promoter sequences (plasmids which were not detectably expressed in vivo) gave rise to a measurable, but smaller level of expression. The stimulation of expression by the 72 bp repeat is cis-acting : it required covalent linkage to the recombinant. We discuss the possibility that the 72 bp repeat region in SV40 may act as a bi-directional entry site for RNA polymerase B such that promoter sequences linked to the repeat are more efficiently utilised.