Evidence from Polygene Mapping for a Causal Relationship between Potato Tuber Dormancy and Abscisic Acid Content

In previous studies polygene mapping of a backcross population derived from haploid potato (Solanum tuberosum) and a diploid wild species (Solanum berthaultii) showed at least eight quantitative trait loci (QTLs) associated with tuber dormancy. The same population was mapped for abscisic acid (ABA) content in tubers so that any QTLs identified could be compared with those detected previously. At least three distinct loci on three chromosomes (2, 4, and 7) were associated with variation in ABA content. One of the QTLs was detected only as a main (single locus) effect, and two QTLs were found through two-locus interaction analysis (epistasis). Interaction between QTLs at markers TG234 (chromosome 2) and TG155 (chromosome 4) explained 20% of total phenotypic variance for this trait. The interaction closely resembled one previously detected for dormancy, suggesting an association between high ABA content and long tuber dormancy. Although relationships between ABA level and dormancy could be demonstrated through polygene mapping, there was no indication of a relationship between these traits when they were subjected to a conventional correlation test. This illustrates the usefulness of polygene mapping as a tool to identify possible associations between hormone levels and plant development.

Reduced expression of tissue transglutaminase in a human endothelial cell line leads to changes in cell spreading, cell adhesion and reduced polymerisation of fibronectin

Tissue transglutaminase (tTgase, type II) is a Ca2+-dependent GTP binding protein which crosslinks proteins via (epsilon)((gamma)-glutamyl)lysine bridges. Although essentially a cytosolic enzyme there is increasing evidence to suggest the enzyme is externalised where it may play a role in extracellular matrix organisation. To investigate the function of this enzyme in a human umbilical endothelial cell line ECV304 tTgase expression was reduced in these cells by up to 90% by stable transfection with a 1.1. kb antisense construct in the plasmid vector pSG5. Two clones showing a reduction in expression of tTgase activity of 70 and 90% have been isolated and characterised. These clones show a number of phenotypic differences when compared to the parent cell line and the transfected controls which include reduced cell spreading and a decreased adhesion of cells on different substrata as measured by their susceptibility to removal by trypsin. Reduced cell spreading in the antisense transfected clones was accompanied by a decrease in the crosslinking of fibronectin into polymeric multimers which could be correlated to the amount of tTgase externalised by cells. A novel assay was developed to measure externalised tTgase activity which is cell mediated, inhibited by preincubation of cells with anti-tTgase antibody and relies on the incorporation of biotinylated cadaverine into fibronectin. The results of these experiments suggest that externalised tTgase may play a key role in a number of cell behavioural patterns which might be related to the enzymes ability to bind and crosslink fibronectin.

Mendel's stem length gene (Le) encodes a gibberellin 3 beta-hydroxylase

We describe the isolation of the Le gene of pea, which controls internode elongation and originally was described by Mendel. Heterologous screening of a pea cDNA library yielded a partial clone that was 61% identical to coding regions of the putative Arabidopsis gibberellin 3 beta-hydroxylase gene, GA4. DNA gel blot analysis with this cDNA revealed a HindIII restriction fragment length polymorphism between pea isolines differing at Mendel's Le locus. Genomic clones of the GA4-related gene were isolated from the Le and le isolines. Polymerase chain reaction combined with restriction fragment length polymorphism analysis were used to show that the gene mapped to the Le locus. A cDNA containing a complete open reading frame of the pea GA4-related gene was amplified by polymerase chain reaction from each isoline. Recombinant expression in Escherichia coli demonstrated that the product of the Le cDNA was a gibberellin 3 beta-hydroxylase that is able to convert GA20 to the bioactive GA1. Substantially reduced levels of gibberellin 3 beta-hydroxylase activity were measured, after expression of the le cDNA, by using identical methods. This reduced activity was associated with an alanine-to-threonine substitution in the predicted amino acid sequence of the enzyme near its proposed active site.

Lack of induction of tissue transglutaminase but activation of the preexisting enzyme in c-Myc-induced apoptosis of CHO cells

The intracellular activity and expression of tissue transglutaminase, which crosslinks proteins through epsilon(gamma-glutamyl)lysine isodipeptide bond, was investigated in CHO cells and those stably transfected with either inducible c-Myc (which leads to apoptosis) or with c-myc and the apoptosis inhibitor Bcl-2. Protein-bound cross-link content was significantly higher when apoptosis was induced by c-Myc while the concomitant presence of Bcl-2 markedly reduced both apoptosis and enzymatic protein cross-linking. The expression of tissue transglutaminase did not change following the initiation of apoptosis by c-Myc or when it was blocked by Bcl-2. Studying transiently co-transfected elements of the mouse tissue transglutaminase promoter linked to a reporter enzyme revealed their overall repression in cells expressing c-Myc. This repression was partially suspended in cells also carrying Bcl-2. Our data suggest that tissue transglutaminase is not induced when c-Myc initiates apoptosis but the pre-existing endogenous enzyme is activated.

tTGase/G alpha h protein expression inhibits adenylate cyclase activity in Balb-C 3T3 fibroblasts membranes

Stably transfected Balb-C 3T3 fibroblasts (clone 5), overexpressing a catalytically active tissue transglutaminase, showed a basal adenylate cyclase activity lower than control cells (clone 1). Several modulators of the adenylate cyclase activity (forskolin, Mn2+ and pertussis toxin) showed the existence of a marked negative control on the adenylate cyclase activity present in clone 5 cells. Very interestingly, this same marked negative control was also found in a Balb-C 3T3 fibroblast clone stably transfected with a mutagenized human tissue transglutaminase (mut277 cys > ser) virtually devoid of transglutaminase catalytic activity (clone Ser). Conversely, a significant increase of the adenylate cyclase activity was observed in bovine aortic endothelial cells after the lowering of tissue transglutaminase expression levels by the transfection of an eukaryotic expression vector containing the gene for tissue transglutaminase in antisense orientation. All these findings suggest a possible role for type II tissue transglutaminase as a negative modulator of the adenylate cyclase activity in different cell types, beside its transglutaminase enzyme activity.

On-going and reflex synaptic events in rat superior cervical ganglion cells

1. Synaptic events evoked by brief noxious cutaneous stimuli were recorded in sympathetic neurones in the superior cervical ganglion of anaesthetized rats. 2. On-going excitatory synaptic potentials (ESPs) and/or action potentials (APs) were recorded in 69% of neurones at mean frequencies that varied from 0.01 to 6.3 Hz in different cells. From histograms of ESP amplitude during membrane hyperpolarization, it appears that most cells received one (52%), or two or more (36%), suprathreshold inputs and several subthreshold inputs with overlapping amplitudes. 3. Pinching the skin for 1-3 s evoked either a brief burst of synaptic events (lasting about 300 ms) preceding a few seconds of inhibition (burst-inhibitory (BI) neurones), or simply an excitation (excitatory (E) neurones), or no response (O neurones). In 60% of BI neurones, a second burst occurred after the end of the pinch. 4. BI neurones had a higher frequency of on-going synaptic activity (2.9 +/- 0.5 Hz, n = 15) than E neurones (0.2 +/- 0.1 Hz, n = 5) or O (0.2 +/- 0.1 Hz, n = 5) neurones. Most neurones with two or more suprathreshold inputs were BI neurones. In 20% of neurones (all BI with high rates of synaptic activity), several other inputs had ESPs with amplitudes close to threshold. 5. Subthreshold and suprathreshold inputs responded in the same way in only 45% of neurones, but suprathreshold inputs were excited in 73% of BI and all E neurones. The order of recruitment of different inputs varied from trial to trial. If classification was based only on suprathreshold responses, there were 36% BI, 32% E and 32% O neurones. 6. In the majority of neurones, postganglionic discharge was initiated exclusively by suprathreshold inputs, even during reflex excitation. 7. Qualitatively similar, but smaller, responses were evoked by a puff of air on the abdomen in 71% of cells tested. 8. The data suggest that the natural discharge of SCG neurones is largely determined by the activity of one or two preganglionic inputs with high quantal contents. BI neurones may include vasoconstrictor neurones, whereas the other types include secretomotor, pilomotor and other neurones projecting to targets in the head.

Regulation of the expression of the tissue transglutaminase gene by DNA methylation

We have investigated the role of DNA methylation in the regulation of the expression of the human tissue transglutaminase gene. Studies on the methylation of the transglutaminase promoter in normal and neoplastic human cells demonstrated that the promoter is methylated in vivo and hypomethylation of the promoter is correlated with constitutive gene expression. Demethylation of the promoter in vivo by treatment of the cells with 5-azacytidine increased transglutaminase expression and hypermethylation of the promoter in vitro suppressed its activity. These studies suggest that alternations in DNA methylation may be one of the mechanisms regulating the tissue-specific expression of the tissue transglutaminase gene.

Sensitization of diabetic and obese mice to insulin by retinoid X receptor agonists

Retinoic acid receptors (RAR), thyroid hormone receptors (TR), peroxisome proliferator activated receptors (PPARs) and the orphan receptor, LXR, bind preferentially to DNA as heterodimers with a common partner, retinoid X receptor (RXR), to regulate transcription. We investigated whether RXR-selective agonists replicate the activity of ligands for several of these receptors? We demonstrate here that RXR-selective ligands (referred to as rexinoids) function as RXR heterodimer-selective agonists, activating RXR: PPARgamma and RXR:LXR dimers but not RXR:RAR or RXR:TR heterodimers. Because PPARgamma is a target for antidiabetic agents, we investigated whether RXR ligands could alter insulin and glucose signalling. In mouse models of noninsulin-dependent diabetes mellitus (NIDDM) and obesity, RXR agonists function as insulin sensitizers and can decrease hyperglycaemia, hypertriglyceridaemia and hyperinsulinaemia. This antidiabetic activity can be further enhanced by combination treatment with PPARgamma agonists, such as thiazolidinediones. These data suggest that the RXR:PPARgamma heterodimer is a single-function complex serving as a molecular target for treatment of insulin resistance. Activation of the RXR:PPARgamma dimer with rexinoids may provide a new and effective treatment for NIDDM.

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.

A novel retinoic acid receptor-selective retinoid, ALRT1550, has potent antitumor activity against human oral squamous carcinoma xenografts in nude mice

We have identified a novel retinoid, ALRT1550, that potently and selectively activates retinoic acid receptors (RARs). ALRT1550 binds RARs with Kd values of approximately equal to 1-4 nM, and retinoid X receptors with low affinities (Kd approximately equal to 270-556 nM). We studied the effects of ALRT1550 on cellular proliferation in squamous carcinoma cells. ALRT1550 inhibited in vitro proliferation of UMSCC-22B cells in a concentration-dependent manner with an IC50 value of 0.22 +/- 0.1 (SE) nM. 9-cis-Retinoic acid (ALRT1057), a pan agonist retinoid that activates RARs and retinoid X receptors, inhibited proliferation with an IC50 value of 81 +/- 29 nM. In vivo, as tumor xenografts in nude mice, UMSCC-22B formed well-differentiated squamous carcinomas, and oral administration (daily, 5 days/week) of ALRT1550, begun 3 days after implanting tumor cells, inhibited tumor growth by up to 89% in a dose-dependent manner over the range of 3-75 micrograms/kg. ALRT1550 (30 micrograms/kg) also inhibited growth of established tumors by 72 +/- 3% when tumors were allowed to grow to approximately equal to 100 mm3 before dosing began. In comparison, 9-cis retinoic acid at 30 mg/kg inhibited growth of established tumors by 73 +/- 5%. Interestingly, retinoids did not appear to alter tumor morphologies in UMSCC-22B tumors. Notably, ALRT1550 produced a therapeutic index of approximately equal to 17 in this model, indicating a separation between doses that inhibited tumor growth and that induced symptoms of hypervitaminosis A. In summary, ALRT1550 potently inhibits cellular proliferation in vitro and in vivo in this squamous cell carcinoma tumor model. These data support additional study of ALRT1550 for its potential for improving anticancer therapy in human clinical trials.

Retinoid-induced epiphyseal plate closure in guinea pigs

Vitamin A and its derivatives (retinoids) have been known to cause premature epiphyseal closure in humans as an unwanted side effect of chronic treatment. The purpose of the present study was to determine if guinea pigs could serve as an animal model of retinoid-induced epiphyseal plate closure, and to utilize this model to study the mechanism. Weanling male Hartley guinea pigs were treated ip via osmotic pump for up to 14 days with vehicle or 0.50 to 5.5 mg/kg/day of the retinoic acid receptor (RAR)-selective agonist AGN 190121. Histopathological examination of the proximal tibia of AGN 190121-treated guinea pigs revealed a dose-dependent disruption of the epiphyseal plate. The natural retinoids all-trans-retinoic acid and 13-cis-retinoic acid also induced epiphyseal plate closure in guinea pigs when administered by ip injection for 10 days. Prominent histological features of retinoid-induced epiphyseal closure included the loss of basophilic staining in the extracellular matrix of epiphyseal plate chondrocytes and the invasion of the epiphyseal plate by osteoclasts. To determine if the epiphyseal closure detected histologically was reversible, guinea pigs were treated for 6 days with the RAR-selective agonist (E)-4[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)propen- 1-y1]benzoic acid (TTNPB) or vehicle, and groups of guinea pigs were euthanized on Day 7 or 57. TTNPB but not vehicle treatment caused histological evidence of epiphyseal closure at both time points, and significant bone elongation between Day 7 and Day 57 was detected only in vehicle-treated animals. Epiphyseal closure and other toxic effects of TTNPB were blocked by cotreatment of guinea pigs with a fivefold molar excess of AGN 193109, an RAR antagonist. Taken together, these data demonstrate the utility of the guinea pig as an animal model of retinoid-induced epiphyseal closure and suggest that RAR activation is necessary and sufficient for this activity.

Identification and functional separation of retinoic acid receptor neutral antagonists and inverse agonists

Inverse agonists are ligands that are capable of repressing basal receptor activity in the absence of an agonist. We have designed a series of C-1-substituted acetylenic retinoids that exhibit potent antagonism of retinoic acid receptor (RAR)-mediated transactivation. Comparison of these related retinoid antagonists for their ability to repress basal RAR transcriptional activity demonstrates that the identity of the C-1 substituent differentiates these ligands into two groups: RAR inverse agonists and neutral antagonists. We show that treatment of cultured human keratinocytes with a RAR inverse agonist, but not a RAR neutral antagonist, leads to the repression of the serum-induced differentiation marker MRP-8. While RAR-selective agonists also repress expression of MRP-8, cotreatment with a RAR inverse agonist and a RAR agonist results in a mutual repression of their individual inhibitory activities, indicating the distinct modes of action of these two disparate retinoids in modulating MRP-8 expression. Our data indicate that RARs, like beta2-adrenoreceptors, are sensitive to inverse agonists and that this new class of retinoids will provide insight into the molecular mechanisms of RAR function in skin and other responsive tissues.

Sources of Ca2+ for different Ca(2+)-activated K+ conductances in neurones of the rat superior cervical ganglion

1. The role of various Ca(2+)-activated K+ conductances were investigated using intracellular recording and single-electrode voltage clamp in neurones of superior cervical ganglia isolated in vitro from young adult rats. 2. Following replacement of Ca2+ with Co2+ (2 mM) or the addition of Cd2+ (100 microM), action potential amplitude and half-width either increased or decreased (in different cells), but both the after-hyperpolarization (AHP) and the outward tail current following a suprathreshold voltage step were markedly attenuated (by about 75%). 3. Addition of charybdotoxin (60 nM) or nifedipine (10 microM) increased action potential half-width (by about 25%) but had no significant effect on the AHP or tail current. 4. Addition of apamin (100 nM) or omega-conotoxin GVIA (100 nM) reduced the AHP and tail current (by about 60%) but did not significantly affect the action potential. A prolonged apamin-resistant component of the AHP present in 50% of neurones was blocked by ryanodine (20 microM). 5. Omega-Conotoxin MVIIC (150 nM) and omega agatoxin IVA (200 nM) had no significant effects on the action potential half-width or the AHP. 6. None of the Ca2+ channel blockers affected the prolonged ryanodine-sensitive component of the AHP and tail current. 7. We conclude that, in rat sympathetic neurones, Ca2+ entry via L-type channels selectively activates large conductance Ca(2+)-activated K+ channels (BK type) contributing to action potential repolarization, whereas Ca2+ entry via N-type channels selectively activates small conductance Ca(2+)-activated K+ channels (SK type) contributing to the AHP. Ca2+ entry via R-type Ca2+ channels prolongs the AHP by activating Ca2+ release from intracellular stores.

Synthesis and structure-activity relationships of retinoid X receptor selective diaryl sulfide analogs of retinoic acid

Retinoids exert their biological effects by binding to and activating nuclear receptors that interact with responsive elements on DNA to promote gene transcription. There are two families of retinoid receptors, the retinoic acid receptor (RAR) family and the retinoid X receptor (RXR) family, which are each further divided into three subclasses: RAR alpha, beta, gamma and RXR alpha, beta, gamma. Herein we describe the synthesis and structure-activity relationships of a new series of diaryl sulfide retinoid analogs that specifically bind and transactivate the RXRs. Furthermore, the sulfoxide and sulfone derivatives of these analogs are partial agonists which activate the RXRs only at high concentrations. Thus, these compounds possess a potential site of metabolic deactivation and may have less prolonged systemic effects than other compounds with arotinoid-like structures. We show also that these compounds have activity in nontransfected cells as demonstrated by their ability to induce TGase activity in HL-60 cells. Finally, we corroborate our earlier report that RXR-specific agonists may possess reduced teratogenic toxicity compared to RAR-specific agonists since these compounds are much less potent inhibitors of chondrogenesis than RAR-specific agonists such as TTNPB.

Retinoic acid induction of the tissue transglutaminase promoter is mediated by a novel response element

We recently cloned and sequenced two kilobases of the upstream flanking region of the mouse tissue transglutaminase gene. Transfection experiments showed that this region of the transglutaminase flanking sequence was sufficient to mediate a 4-fold induction in reporter gene expression by retinoic acid. The goal of these studies was to identify retinoid receptor binding sites within this proximal 2 kilobase sequence and then to determine if these binding sites had ligand-dependent enhancer activity. To accomplish this we first employed a competitive band-shift assay using PCR-synthesized genomic DNA fragments as probes. This assay identified a receptor binding site located 1.7 Kb upstream from the transcription start site that contained three consensus hexanucleotide 'half sites' separated by 7 and 5 bp, respectively. This tripartite response element was shown to mediate retinoic acid activation of a heterologous promoter in transient transfection assays in RAW264.7 cells. Our results suggest that this novel retinoid response element is responsible for the retinoic acid induction of mouse tissue transglutaminase gene expression observed in numerous cells.

Retinoid-regulated expression of BCL-2 and tissue transglutaminase during the differentiation and apoptosis of human myeloid leukemia (HL-60) cells

Retinoids induce terminal differentiation and subsequent apoptosis in the human myeloid leukemia (HL-60) cell line. We have previously shown that in HL-60 cells, ligand activation of retinoic acid receptors (RARs) is sufficient to induce differentiation but ligand activation of retinoid X receptors (RXRs) is necessary for the retinoid-induced apoptosis of these cells. In the present studies we have characterized the effect of retinoids on the expression of two apoptosis-linked gene products, BCL-2 and tissue transglutaminase. BCL-2 is a membrane-associated protein whose expression has been linked to the suppression of apoptosis in many cells. Tissue transglutaminase is a protein cross-linking enzyme that accumulates in many cells undergoing apoptotic cell death. Our data suggest that ligand activation of RARs in HL-60 cells results in a global suppression of BCL-2 expression whereas ligand activation of both RARs and RXRs triggers the selective accumulation of tissue transglutaminase in the apoptotic HL-60 cells.

Purchasing post-qualifying professional education in the health care sector

The National Health Service (NHS) is proposing to establish local consortia for educational contracting, with wider involvement and responsibility being devolved to service managers. This paper addresses the educational issues of purchasing post-qualifying professional education for a cross-section of NHS hospital professionals. The professions chosen for comparison were clinical staff and include nurses, doctors, and as an example of paramedical professions', physiotherapists.

Enhanced antitumor efficacy of cisplatin in combination with ALRT1057 (9-cis retinoic acid) in human oral squamous carcinoma xenografts in nude mice

Cisplatin (DDP) is commonly used to treat head and neck tumors. Therapy frequently fails due to development of DDP resistance or toxicities associated with DDP therapy. In this study, effects of ALRT1057 [9-cis retinoic acid (9-cis RA)] on DDP cytotoxicity were studied in a human oral squamous carcinoma xenograft model. Mice bearing xenografts were dosed p.o. daily 5 days/week with 30 mg/kg 9-cis RA and/or i.p. twice weekly with 0.3-0.9 mg/kg DDP. Maximum tolerated doses of 9-cis RA and DDP were approximately 60 and >/=2.9 mg/kg, respectively, under their dosing schedules and routes of administration. Control tumors grew rapidly with mean doubling times of 4 +/- 1 days and reached mean volumes of 1982 +/- 199 (SE) mm3 after 24 days. DDP at doses of 0.3, 0.45, and 0.9 mg/kg inhibited tumor growth by 28, 47, and 86%, respectively, 24 days after tumor cell implantation. Thirty mg/kg 9-cis RA inhibited tumor growth by 25%. In combination, 0.3 mg/kg DDP + 30 mg/kg 9-cis RA inhibited tumor growth by 68%; 0.45 mg/kg DDP + 30 mg/kg 9-cis RA inhibited growth by 78%. These decreases were greater than those that would have been produced by either agent summed separately. Of importance, at doses of 9-cis RA that enhanced DDP cytotoxicity, no change in dose tolerance was observed as compared to tolerances observed for either agent alone, indicating that 9-cis RA increased sensitivity to DDP without altering systemic toxicity. In addition, 9-cis RA profoundly altered squamous cell carcinoma phenotypes by suppressing squamous cell differentiation, resulting in tumors with increased numbers of basal cells. In contrast, DDP selectively depleted proliferating basal cells from carcinomas. In combination, morphological changes produced by 9-cis RA alone predominated, suggesting a possible basis for enhanced DDP sensitivity in tumors exposed to both agents. These data demonstrate that 9-cis RA enhances tumor sensitivity to DDP, and suggest that this combination should be tested in Phase I-II clinical trials for its potential for improving anticancer therapy of squamous cell cancers.

Genetic Dissection of the Relative Roles of Auxin and Gibberellin in the Regulation of Stem Elongation in Intact Light-Grown Peas

Exogenous gibberellin (GA) and auxin (indoleacetic acid [IAA]) strongly stimulated stem elongation in dwarf GA1-deficient le mutants of light-grown pea (Pisum sativum L.): IAA elicited a sharp increase in growth rate after 20 min followed by a slow decline; the GA response had a longer lag (3 h) and growth increased gradually with time. These responses were additive. The effect of GA was mainly in internodes less than 25% expanded, whereas that of IAA was in the older, elongating internodes. IAA stimulated growth by cell extension; GA stimulated growth by an increase in cell length and cell number. Dwarf lkb GA-response-mutant plants elongated poorly in response to GA (accounted for by an increase in cell number) but were very responsive to IAA. GA produced a substantial elongation in lkb plants only in the presence of IAA. Because lkb plants contain low levels of IAA, growth suppression in dwarf lkb mutants seems to be due to a deficiency in endogenous auxin. GA may enhance the auxin induction of cell elongation but cannot promote elongation in the absence of auxin. The effect of GA may, in part, be mediated by auxin. Auxin and GA control separate processes that together contribute to stem elongation. A deficiency in either leads to a dwarfed phenotype.

Identification and characterization of a versatile retinoid response element (retinoic acid receptor response element-retinoid X receptor response element) in the mouse tissue transglutaminase gene promoter

Tissue transglutaminase (transglutaminase type II) is an intracellular protein cross-linking enzyme that accumulates in connective tissue and in cells undergoing apoptosis. Retinoids regulate the transcription of the mouse tissue transglutaminase gene via activation of regulatory elements contained within 4 kilobases of the 5'-end of the gene. Co-transfection studies with retinoid receptor expression vectors in CV-1 cells demonstrated that the mouse tissue transglutaminase promoter is activated by ligand activation of either retinoic acid receptor-retinoid X receptor (RAR.RXR) heterodimers or RXR homodimers. Optimal induction is achieved with retinoid receptor panagonists; partial activation can also be achieved with either RAR-specific or RXR-specific retinoids. Retinoid-dependent activation of the tissue transglutaminase promoter depends on both a proximal regulatory region containing sequences highly conserved between the human and the mouse tissue transglutaminase promoters and a distal region that includes a 30-base pair retinoid response element (mTGRRE1). mTGRRE1 contains three hexanucleotide half-sites (two canonical and one non-canonical) in a DR7/DR5 motif that bind both RAR*RXR heterodimers and RXR homodimers. These studies suggest that retinoid-dependent expression of the mouse tissue transglutaminase gene is mediated by a versatile tripartite retinoid response element located 1.7 kilobases upstream of the transcription start site.

The importance of the GTP-binding protein tissue transglutaminase in the regulation of cell cycle progression

Tissue transglutaminase (tTgase) is a GTP-binding Ca(2+)-dependent enzyme which catalyses the post-translational modification of proteins via epsilon(gamma-glutamyl) lysine bridges. Recent evidence suggests that the GTP-binding activity of tTgase may be important in intracellular signaling thus explaining some of the diverse suggested roles for the enzyme. In the following work a malignant hamster fibrosarcoma (Met B) has been stably transfected with both the full length tTgase cDNA (wild type) and a mutant form of the cDNA whereby the active site cysteine (Cys 277) has been replaced by serine. Expression of this mutant cDNA leads to a protein with GTP binding activity which is deficient of protein crosslinking activity. When synchronised into S-phase and allowed to progress through the cell cycle tTgase transfected clones (both mutant and wild type), when compared to transfected controls, show a delayed progression from S-phase to G2/M when analysed by flow cytometry which appears to be elicited by the G-protein activity of the tTgase.

Retinoid-induced suppression of squamous cell differentiation in human oral squamous cell carcinoma xenografts (line 1483) in athymic nude mice

Retinoids are promising agents for therapy of squamous cancers. In vitro, retinoids decrease expression of differentiation markers in head and neck squamous carcinoma cells. Little information is available on effects of retinoids on head and neck squamous carcinoma cell xenograft growth in vivo. To address this issue, head and neck squamous carcinoma cells (line 1483) were established as xenografts in nude mice. Control tumors grew rapidly with doubling times of 4-6 days to mean volumes of 1696 mm3 after 24 days. Histological analyses indicated the formation of well-differentiated squamous carcinoma cells exhibiting pronounced stratification (basal and suprabasal cells) and keratinization (keratin pearls) with abundant stroma. Cytokeratin 19 expression was restricted to the basal cell layers, and cytokeratin 4 expression was abundant in suprabasal cells. Mice were treated daily with 30 mg/kg 9-cis retinoic acid, 20 mg/kg all-trans-retinoic acid, or 60 mg/kg 13-cis retinoic acid by p.o. gavage on a schedule of 5 days/week over 4 weeks. Low micromolar (1.48-3.67 microM) and nanomolar (200-490 nM) concentrations of 9-cis retinoic acid and all-trans-retinoic acid were measured in plasmas and xenografts, respectively, 30 min after dosing. Retinoid treatment produced a marked suppression of the squamous cell differentiation of tumor cells manifest by decreased keratinization, loss of stratification, and accumulation of basal cells. This was accompanied by large decreases in the number of CK4-positive cells and concomitant increases of CK19-positive cells. REtinoic acid receptor-beta expression was also increased by 2.9-9.7-fold after chronic retinoid treatment. 9-cis retinoic acid and all-trans-retinoic acid decreased tumor volumes by 23 +/- 5 (SE) and 19 +/- 3%, respectively (P < or = 0.05); 13-cis retinoic acid was inactive. These retinoids did not decrease the rate of exponential tumor growth but increased the latent period until exponential growth began. These studies demonstrate that retinoids do not universally decrease tumor growth but profoundly suppress squamous cell differentiation in vivo in this xenograft model.