Inhibition of Aurora Kinase Induces Endogenous Retroelements to Induce a Type I/III IFN Response via RIG-I

Type I IFN signaling is a crucial component of antiviral immunity that has been linked to promoting the efficacy of some chemotherapeutic drugs. We developed a reporter system in HCT116 cells that detects activation of the endogenous IFI27 locus, an IFN target gene. We screened a library of annotated compounds in these cells and discovered Aurora kinase inhibitors (AURKi) as strong hits. Type I IFN signaling was found to be the most enriched gene signature after AURKi treatment in HCT116, and this signature was also strongly enriched in other colorectal cancer cell lines. The ability of AURKi to activate IFN in HCT116 was dependent on MAVS and RIG-I, but independent of STING, whose signaling is deficient in these cells. MAVS dependence was recapitulated in other colorectal cancer lines with STING pathway deficiency, whereas in cells with intact STING signaling, the STING pathway was required for IFN induction by AURKi. AURKis were found to induce expression of endogenous retroviruses (ERV). These ERVs were distinct from those induced by the DNA methyltransferase inhibitors (DNMTi), which can induce IFN signaling via ERV induction, suggesting a novel mechanism of action. The antitumor effect of alisertib in mice was accompanied by an induction of IFN expression in HCT116 or CT26 tumors. CT26 tumor growth inhibition by alisertib was absent in NSG mice versus wildtype (WT) mice, and tumors from WT mice with alisertib treatment showed increased in CD8+ T-cell infiltration, suggesting that antitumor efficacy of AURKi depends, at least in part, on an intact immune response.

SIGNIFICANCE

Some cancers deactivate STING signaling to avoid consequences of DNA damage from aberrant cell division. The surprising activation of MAVS/RIG-I signaling by AURKi might represent a vulnerability in STING signaling deficient cancers.

Differential effects of targeting Notch receptors in a mouse model of liver cancer

Primary liver cancer encompasses both hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA). The Notch signaling pathway, known to be important for the proper development of liver architecture, is also a potential driver of primary liver cancer. However, with four known Notch receptors and several Notch ligands, it is not clear which Notch pathway members play the predominant role in liver cancer. To address this question, we utilized antibodies to specifically target Notch1, Notch2, Notch3, or jagged1 (Jag1) in a mouse model of primary liver cancer driven by v-akt murine thymoma viral oncogene homolog and neuroblastoma RAS viral oncogene homolog (NRas). We show that inhibition of Notch2 reduces tumor burden by eliminating highly malignant HCC- and CCA-like tumors. Inhibition of the Notch ligand, Jag1, had a similar effect, consistent with Jag1 acting in cooperation with Notch2. This effect was specific to Notch2, because Notch3 inhibition did not decrease tumor burden. Unexpectedly, Notch1 inhibition altered the relative proportion of tumor types, reducing HCC-like tumors but dramatically increasing CC-like tumors. Finally, we show that Notch2 and Jag1 are expressed in, and Notch2 signaling is activated in, a subset of human HCC samples.

CONCLUSIONS

These findings underscore the distinct roles of different Notch receptors in the liver and suggest that inhibition of Notch2 signaling represents a novel therapeutic option in the treatment of liver cancer.

Therapeutic antibody targeting of individual Notch receptors

The four receptors of the Notch family are widely expressed transmembrane proteins that function as key conduits through which mammalian cells communicate to regulate cell fate and growth. Ligand binding triggers a conformational change in the receptor negative regulatory region (NRR) that enables ADAM protease cleavage at a juxtamembrane site that otherwise lies buried within the quiescent NRR. Subsequent intramembrane proteolysis catalysed by the gamma-secretase complex liberates the intracellular domain (ICD) to initiate the downstream Notch transcriptional program. Aberrant signalling through each receptor has been linked to numerous diseases, particularly cancer, making the Notch pathway a compelling target for new drugs. Although gamma-secretase inhibitors (GSIs) have progressed into the clinic, GSIs fail to distinguish individual Notch receptors, inhibit other signalling pathways and cause intestinal toxicity, attributed to dual inhibition of Notch1 and 2 (ref. 11). To elucidate the discrete functions of Notch1 and Notch2 and develop clinically relevant inhibitors that reduce intestinal toxicity, we used phage display technology to generate highly specialized antibodies that specifically antagonize each receptor paralogue and yet cross-react with the human and mouse sequences, enabling the discrimination of Notch1 versus Notch2 function in human patients and rodent models. Our co-crystal structure shows that the inhibitory mechanism relies on stabilizing NRR quiescence. Selective blocking of Notch1 inhibits tumour growth in pre-clinical models through two mechanisms: inhibition of cancer cell growth and deregulation of angiogenesis. Whereas inhibition of Notch1 plus Notch2 causes severe intestinal toxicity, inhibition of either receptor alone reduces or avoids this effect, demonstrating a clear advantage over pan-Notch inhibitors. Our studies emphasize the value of paralogue-specific antagonists in dissecting the contributions of distinct Notch receptors to differentiation and disease and reveal the therapeutic promise in targeting Notch1 and Notch2 independently.

TGFbeta-stimulated Smad1/5 phosphorylation requires the ALK5 L45 loop and mediates the pro-migratory TGFbeta switch

During the course of breast cancer progression, normally dormant tumour-promoting effects of transforming growth factor beta (TGFbeta), including migration, invasion, and metastasis are unmasked. In an effort to identify mechanisms that regulate the pro-migratory TGFbeta 'switch' in mammary epithelial cells in vitro, we found that TGFbeta stimulates the phosphorylation of Smad1 and Smad5, which are typically associated with bone morphogenetic protein signalling. Mechanistically, this phosphorylation event requires the kinase activity and, unexpectedly, the L45 loop motif of the type I TGFbeta receptor, ALK5, as evidenced by studies using short hairpin RNA-resistant ALK5 mutants in ALK5-depleted cells and in vitro kinase assays. Functionally, Smad1/5 co-depletion studies demonstrate that this phosphorylation event is essential to the initiation and promotion of TGFbeta-stimulated migration. Moreover, this phosphorylation event is preferentially detected in permissive environments such as those created by tumorigenic cells or oncogene activation. Taken together, our data provide evidence that TGFbeta-stimulated Smad1/5 phosphorylation, which occurs through a non-canonical mechanism that challenges the notion of selective Smad phosphorylation by ALK5, mediates the pro-migratory TGFbeta switch in mammary epithelial cells.

Clinicopathologic features of breast disease in Jamaica: findings of the Jamaican Breast Disease Study, 2000-2002

OBJECTIVE

To describe the clinicopathologic profile of breast disease in Jamaica.

METHODS

The Jamaican Breast Disease Study is an ongoing prospective, multidisciplinary investigation of breast disease at the University Hospital of the West Indies (UHWI). The initial phase was a prevalence survey comprising all consenting patients referred to the Surgical Outpatient Department (SOPD) UHWI, for breast disease. Demographic, clinical, radiologic and pathologic information were recorded for each patient and the data for the first three years (2000-2002) were analyzed.

RESULTS

A total of 1189 patients was enrolled for the study period (28.8% of all new SOPD patients). The age range was 10 to 93 years (mean/SD = 36.5 +/- 16.4 years) with a female : male ratio of 14:1. Most patients (67.8%) presented with a palpable lump and the clinical diagnosis was benign in the majority (70.4%) of patients. Fibroadenoma was the most common benign histologic result (39.4% of all biopsies) followed by non-proliferative (fibrocystic) disease (19.3% of all biopsies). Proliferative disease without atypia, complex fibroadenoma and atypical ductal hyperplasia accounted for 6.9%, 2.6% and 0.4% of biopsies respectively. Overall, 23.4% of biopsies showed malignant histology (10.8% patients); invasive ductal carcinoma accounted for the majority of these cases (69.5%).

CONCLUSIONS

The majority of patients with breast disease in Jamaica are young women with clinically benign disease. There was a low prevalence of clinically significant premalignant disease. This is the first study to prospectively describe the clinicopathologic features of breast disease in Jamaica and supports the need for advocating breast cancer screening to facilitate detection of significant premalignant disease and early stages of breast cancer.

Transforming growth factor beta/Smad3 signaling regulates IRF-7 function and transcriptional activation of the beta interferon promoter

The rapid induction of alpha interferon (IFN-alpha) and IFN-beta expression plays a critical role in the innate immune response against viral infection. We studied the effects of transforming growth factor beta (TGF-beta) and its intracellular effectors, the Smads, on the function of IRF-7, an essential transcription factor for IFN-alpha and -beta induction. IRF-7 interacted with Smads, and IRF-7, but not IRF-3, cooperated with Smad3 to activate IFN-beta transcription. This transcriptional cooperation occurred at the IRF-binding sequences in the IFN-beta promoter, and dominant-negative interference with TGF-beta receptor signaling and Smad3 function decreased IRF-7-mediated transcription. Furthermore, elimination of Smad3 expression in Smad3(-/-) fibroblasts delayed and decreased double-stranded RNA-induced expression of endogenous IFN-beta, whereas restoration of Smad3 expression enhanced IFN-beta induction. The IRF-7-Smad3 cooperativity resulted from the regulation of the transactivation activity of IRF-7 by Smad3, and dominant-negative interference with Smad3 function decreased IRF-7 activity. Consistent with the regulation by Smad3, the transcriptional activity of IRF-7 depended on and was regulated by TGF-beta signaling. Our studies underscore a role of TGF-beta/Smad3 signaling in IRF-7-mediated induction of IFN-beta expression.

Transforming growth factor-beta inhibits adipocyte differentiation by Smad3 interacting with CCAAT/enhancer-binding protein (C/EBP) and repressing C/EBP transactivation function

Transforming growth factor (TGF)-beta is a potent inhibitor of adipocyte differentiation. To identify which adipocyte transcription factors might be targeted by TGF-beta, we overexpressed key adipogenic transcription factors, C/EBPbeta, C/EBPdelta, or peroxisome proliferator-activated receptor (PPAR) gamma in NIH3T3 cells and tested the ability of TGF-beta to block adipogenesis. We show that TGF-beta inhibits adipocyte differentiation driven by either C/EBPbeta or C/EBPdelta without affecting C/EBP protein expression levels, suggesting that these C/EBPs are a direct target of TGF-beta action. Because TGF-beta inhibits adipogenesis by signaling through Smad3, we examined physical and functional interactions of Smad3 and Smad4 with C/EBPbeta, C/EBPdelta, and PPARgamma2. C/EBPbeta and C/EBPdelta were found to physically interact with Smad3 and Smad4, and Smad3 cooperated with Smad4 and TGF-beta signaling to repress the transcriptional activity of C/EBPs. Thus, repression of the activity of C/EBPs by Smad3/4 at C/EBP binding sites inhibited transcription from the PPARgamma2 and leptin promoters. In contrast, PPARgamma interacted only very weakly with Smad3 and its transcriptional activity was not repressed by Smad3/4 or in response to TGF-beta. Smad3/4 did not reduce the ability of C/EBP to bind to its cognate DNA sequence, but repressed transcription by inhibiting the transactivation function of C/EBP.

Bone morphogenetic protein and retinoic acid signaling cooperate to induce osteoblast differentiation of preadipocytes

Mesenchymal cells can differentiate into osteoblasts, adipocytes, myoblasts, or chondroblasts. Whether mesenchymal cells that have initiated differentiation along one lineage can transdifferentiate into another is largely unknown. Using 3T3-F442A preadipocytes, we explored whether extracellular signals could redirect their differentiation from adipocyte into osteoblast. 3T3-F442A cells expressed receptors and Smads required for bone morphogenetic protein (BMP) signaling. BMP-2 increased proliferation and induced the early osteoblast differentiation marker alkaline phosphatase, yet only mildly affected adipogenic differentiation. Retinoic acid inhibited adipose conversion and cooperated with BMP-2 to enhance proliferation, inhibit adipogenesis, and promote early osteoblastic differentiation. Expression of BMP-RII together with BMP-RIA or BMP-RIB suppressed adipogenesis of 3T3-F442A cells and promoted full osteoblastic differentiation in response to retinoic acid. Osteoblastic differentiation was characterized by induction of cbfa1, osteocalcin, and collagen I expression, and extracellular matrix calcification. These results indicate that 3T3-F442A preadipocytes can be converted into fully differentiated osteoblasts in response to extracellular signaling cues. Furthermore, BMP and retinoic acid signaling cooperate to stimulate cell proliferation, repress adipogenesis, and promote osteoblast differentiation. Finally, BMP-RIA and BMP-RIB induced osteoblast differentiation and repressed adipocytic differentiation to a similar extent.

TGF-beta-induced repression of CBFA1 by Smad3 decreases cbfa1 and osteocalcin expression and inhibits osteoblast differentiation

Transforming growth factor-beta (TGF-beta), a secreted factor present at high levels in bone, inhibits osteoblast differentiation in culture; yet, the mechanism of this inhibition remains unclear. We studied the effects of TGF-beta and its effectors, the Smads, on the expression and function of the osteoblast transcription factor CBFA1. TGF-beta inhibited the expression of the cbfa1 and osteocalcin genes, whose expression is controlled by CBFA1 in osteoblast-like cell lines. This inhibition was mediated by Smad3, which interacts physically with CBFA1 and represses its transcriptional activity at the CBFA1-binding OSE2 promoter sequence. The repression of CBFA1 function by Smad3 contrasts with previous observations that Smads function as transcription activators. This repression occurred in mesenchymal but not epithelial cells, and depended on the promoter sequence. Smad3-mediated repression of CBFA1 provides a central regulatory mechanism for the inhibition of osteoblast differentiation by TGF-beta, since it inhibits both cbfa1 transcription and transcriptional activation of osteoblast differentiation genes by CBFA1. Altering Smad3 signaling influenced osteoblast differentiation in the presence or absence of TGF-beta, implicating Smad3/TGF-beta-mediated repression in autocrine regulation of osteoblast differentiation.

Salivary gland lesions: a Jamaican perspective

A retrospective analysis of the spectrum and relative frequency of salivary gland lesions diagnosed in the Department of Pathology, University of the West Indies, Kingston, Jamaica, between 1965 and 1994, is reported. Four hundred and sixty-four salivary gland biopsies were received. Of these 99 (21.3%) were non-neoplastic and the remaining 365 (78.7%) were neoplasms: 261 (71.5%) were benign and 104 (28.5%) malignant. Benign mixed tumour (BMT)/pleomorphic adenoma (PA) was the most common neoplasm (63.3%) while mucoepidermoid carcinoma (MEC) was the most common malignant neoplasm (9.6%), followed by adenoid cystic carcinoma (ACC) (7.4%). The increased frequency of MEC over ACC is at variance with other reported series but the preponderance of pleomorphic adenoma is consistent. In the major salivary glands, benign neoplasms predominate at a ratio of 3:1, while a higher proportion of minor salivary gland neoplasms was malignant, ratio 1.2:1 (p = 0.003). These data represent the first attempt to document the spectrum of disease related to oral and maxillofacial pathology in Jamaica.

Smad7 is induced by CD40 and protects WEHI 231 B-lymphocytes from transforming growth factor-beta -induced growth inhibition and apoptosis

Transforming growth factor-beta (TGF-beta) is a potent inducer of apoptosis in B-lymphocytes and is essential for immune regulation and maintenance of self-tolerance. Here we show that concomitant signaling through CD40 sustains proliferation and rescues the premature B cell line WEHI 231 from both TGF-beta-induced and anti-IgM-induced apoptosis. The anti-apoptotic effect of CD40 is associated with the transcriptional activation of the inhibitory Smad7 protein. The transactivation of Smad7 by CD40 is NFkappaB-dependent in that pharmacological inhibitors of this pathway, N-tosyl-l-phenylalanine chloromethyl ketone and pyrrolidine dithiocarbamate, abrogate CD40-induced Smad7 expression. Ectopic overexpression of Smad7 inhibited Smad2 activation, TGF-beta-mediated growth inhibition, and apoptosis in WEHI 231 cells. Consistent with this result, dominant negative interference with Smad2 and Smad3 function also inhibited TGF-beta-induced apoptosis. The inhibitory effects of Smad7 overexpression were specific to TGF-beta-induced apoptosis and were without effect on anti-IgM-induced cell death. These results suggest a mechanism of suppression of TGF-beta-induced apoptosis by CD40, mediated through activation of NF-kappaB and, consequently, induction of Smad7 expression.

Roles of autocrine TGF-beta receptor and Smad signaling in adipocyte differentiation

TGF-beta inhibits adipocyte differentiation, yet is expressed by adipocytes. The function of TGF-beta in adipogenesis, and its mechanism of action, is unknown. To address the role of TGF-beta signaling in adipocyte differentiation, we characterized the expression of the TGF-beta receptors, and the Smads which transmit or inhibit TGF-beta signals, during adipogenesis in 3T3-F442A cells. We found that the cell-surface availability of TGF-beta receptors strongly decreased as adipogenesis proceeds. Whereas mRNA levels for Smads 2, 3, and 4 were unchanged during differentiation, mRNA levels for Smads 6 and 7, which are known to inhibit TGF-beta responses, decreased severely. Dominant negative interference with TGF-beta receptor signaling, by stably expressing a truncated type II TGF-beta receptor, enhanced differentiation and decreased growth. Stable overexpression of Smad2 or Smad3 inhibited differentiation and dominant negative inhibition of Smad3 function, but not Smad2 function, enhanced adipogenesis. Increased Smad6 and Smad7 levels blocked differentiation and enhanced TGF-beta-induced responses. The inhibitory effect of Smad7 on adipocyte differentiation and its cooperation with TGF-beta was associated with the C-domain of Smad7. Our results indicate that endogenous TGF-beta signaling regulates the rate of adipogenesis, and that Smad2 and Smad3 have distinct functions in this endogenous control of differentiation. Smad6 and Smad7 act as negative regulators of adipogenesis and, even though known to inhibit TGF-beta responses, enhance the effects of TGF-beta on these cells.

Comparison of lignocaine-prilocaine cream and amethocaine gel for local analgesia before venepuncture in children

The efficacy of lignocaine-prilocaine cream (EMLA) and amethocaine gel (Ametop) in reducing the pain and distress of venepuncture was compared in a single-blind randomized study of 34 children aged 1-14 y. The influences of age, anxiety and past experience were also investigated. Pain was assessed by the researcher using the Observation Scale of Behavioural Distress, and by the parent, doctor and child (if old enough) using a 10-cm, 100-point Visual Analogue Scale (VAS). Doctors also completed a simple rating scale for difficulty of venepuncture. Compared to older children, infants had significantly more anxious parents and were more distressed when being held still. Anticipatory anxiety correlated with higher pain ratings. No differences in the analgesic effect of the two preparations were found. We conclude that whilst EMLA and Ametop are equally effective at reducing the pain of needle puncture, under some circumstances the use of Ametop may be more advantageous.

The type II transforming growth factor (TGF)-beta receptor-interacting protein TRIP-1 acts as a modulator of the TGF-beta response

The transforming growth factor-beta (TGF-beta) receptor interacting protein TRIP-1 was originally identified as a WD40 repeat-containing protein that has the ability to associate with the TGF-beta type II receptor and is phosphorylated by it (1). However, its function was not known. We now show that TRIP-1 expression represses the ability of TGF-beta to induce transcription from the plasminogen activator inhibitor-1 promoter, a common reporter of the TGF-beta-induced gene expression response, but does not affect the ability of TGF-beta to inhibit cyclin A transcription. TRIP-1 can also inhibit the plasminogen activator inhibitor-1 expression induced by Smads as well as activated TGF-beta type I receptors. Its inhibitory effect is exerted by a combination of receptor-dependent and receptor-independent mechanisms. Deletion mutational analysis revealed that two distinct regions, which do not contain recognizable WD40 repeats, are required for the ability of TRIP-1 to inhibit the gene expression response. Expression of other segments of TRIP-1 increased the TGF-beta-induced gene expression response and therefore may exert a dominant negative phenotype. We conclude that TRIP-1 acts as a modulator of the TGF-beta response.

A WD-domain protein that is associated with and phosphorylated by the type II TGF-beta receptor

Transforming growth factor-beta (TGF-beta) is the prototype for a family of extracellular polypeptides that affect cell proliferation and differentiation, and tissue morphogenesis. TGF-beta signalling is mediated by two types of serine/threonine kinase receptors, the type I and II receptors, which are able to form a heteromeric complex. No cytoplasmic proteins that associate with these receptors in vivo, or are their kinase targets, have yet been described. We have now identified a WD-domain-containing protein, TRIP-1, which specifically associates with the type II TGF-beta receptor in a kinase-dependent way. TRIP-1 does not interact with the type II activin or type I receptors, but associates with the heteromeric TGF-beta receptor complex. TRIP-1 is phosphorylated on serine and threonine by the receptor kinase, strongly suggesting that it has a role in TGF-beta signalling. This is supported by coexpression of TRIP-1 and type II receptor during development. The existence of TRIP-1 homologues in plant and yeast suggests a conserved function in all eukaryotes.

Characterization of the novel brown adipocyte cell line HIB 1B. Adrenergic pathways involved in regulation of uncoupling protein gene expression

The HIB 1B cell line, derived from a brown fat tumor of a transgenic mouse, is the first established brown adipocyte cell line capable of expressing the brown fat-specific mitochondrial uncoupling protein (UCP). UCP gene expression, which was virtually undetectable under basic conditions, was stimulated by acute catecholamine or cyclic AMP treatment to levels comparable to primary cultures of brown adipocytes. Elevation of UCP mRNA levels following stimulation was very rapid but transient, decreasing after about 4 hours with a half-life between 9 and 13 hours. Immunoblotting showed the presence of UCP in HIB 1B mitochondria, but expression was much lower than observed in BAT or primary cultures of brown adipocytes. Upon transfection of HIB 1B cells with a reporter gene containing the UCP promoter, the activity of the transgene was regulatable by cAMP and norepinephrine. Investigation of the possible adrenergic receptors involved in UCP stimulation showed that specific beta 3-adrenergic agonists were much less effective than nonspecific beta-adrenergic agonists and that mRNA levels of the atypical, fat-specific beta 3-adrenoceptor were lower than those observed in brown adipocytes differentiated in primary culture. From pharmacological evidence we conclude that beta 3-adrenergic receptors account for approximately 30–40% of catecholamine induced UCP gene stimulation, whereas about 60–70% is stimulated via the classical beta 1/2 adrenergic pathway. We conclude that HIB 1B cells represent a functional system for the study of mechanisms related to brown adipose thermogenesis.

Hibernoma formation in transgenic mice and isolation of a brown adipocyte cell line expressing the uncoupling protein gene

Transgenic mice were produced containing the adipocyte-specific regulatory region from the adipocyte P2 (aP2) gene linked to the simian virus 40 transforming genes. Most of the transgenic mice developed brown fat tumors (hibernomas) in their interscapular brown adipose tissue. Hibernoma formation was noticeable in some of the mice as early as 1 day after birth and most of the mice developed very large tumors by 1 month of age. All of the tumor tissue expressed the brown fat-specific uncoupling protein (UCP) gene as well as the aP2 gene. Several of the tumors have been used to establish cultured cell lines and at least one of these lines can be induced to differentiate into brown adipocytes. The cultured adipocytes express mRNA for UCP upon stimulation with N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate, norepinephrine, isoproterenol or D7114, a beta 3 adrenergic agonist. Thus, regulation of the key thermogenic gene UCP can now be studied in an established cell line.

Biosynthetic regulation of monobutyrin, an adipocyte-secreted lipid with angiogenic activity

1-Butyrylglycerol (monobutyrin) is a novel angiogenic compound that is synthesized and secreted during the differentiation of 3T3-F442A preadipocytes into adipocytes. To study the regulation of monobutyrin biosynthesis we have developed an assay utilizing the lgycerol kinase enzyme from Cellulomonas to quantitate the levels of this compound in cell-conditioned medium. Analysis of several cultured cell types, including tumor cell lines, indicated that monobutyrin production is detectable only from adipocytes, reaching a steady-state concentration of approximately 1.0 microM in conditioned medium. Monobutyrin synthesis was demonstrated in vitro using [14C]butyryl-CoA with total homogenate or particulate fractions from adipocytes. Similar fractions from non-adipocyte cell lines failed to synthesize monobutyrin. This biosynthetic activity was shown to be distinct by substrate competition studies from the microsomal sn-glycerol-3-phosphate acyltransferase, whose activity is known to increase during adipocyte differentiation. The production of monobutyrin was hormonally regulated, as the addition of epinephrine to adipocytes caused a 10-fold increase in the amount of monobutyrin secreted. These results indicate that monobutyrin synthesis is adipocyte specific, occurs through an apparently novel particulate enzyme system, and is regulated in a hormone-dependent manner. The implications of these results for adipose physiology and angiogenesis are discussed.

Interaction of nuclear factors with upstream sequences of a lipid body membrane protein gene from carrot

To study the regulation of gene expression during embryo development, we isolated a gene, DC 59, expressed in embryos but not in mature carrot plants. Sequence and S1 analysis showed that the gene was composed of one exon encoding a polypeptide of 19 kilodaltons and was highly homologous to the lipid body membrane protein gene L3 from maize. The plant hormone abscisic acid regulated the accumulation of DC 59 mRNA. To understand the mechanism of embryo-specific and hormonal regulation of DC 59, 5' DNA fragments were incubated with nuclear proteins. Two adjacent regions (from -706 to -235) interacted with nuclear extracts from embryos, resulting in the formation of four complexes (C1, C2, C3, and C4). Factors involved in the formation of the C3 and C4 complexes could be competed with sequences upstream of DC 8, a gene that is coordinately expressed with DC 59 during embryo development. DNase I footprinting analysis revealed that nuclear extracts from embryos bound to four AT-rich sequences, and the protected motifs within fragment V were located in the highly homologous upstream regions of DC 59 and DC 8 genes.