High frequency of carcinogen-induced early, preneoplastic changes in rat tracheal epithelial cells in culture.

To study the mechanisms of carcinogenesis, we have developed a system that uses normal cells from an environmentally and epidemiologically relevant tissue, respiratory epithelium. The induction of preneoplastic variants of epithelial cells in culture was quantitated on a per-cell basis following exposure of rat tracheal epithelial (RTE) cells in vitro to the direct-acting carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Following treatment of normal RTE cells, large colonies of altered cells exhibiting an enhanced growth potential under selective culture conditions were observed, while normal RTE cells ceased proliferation after several cell doublings. After further growth in culture, these altered cells acquired the ability to grow in semisolid medium and to produce squamous cell carcinomas when injected into nude mice. The induction of enhanced growth variants of RTE cells by MNNG occurred with a high frequency (greater than or equal to 2.6%/colony-forming cell). In addition, a linear dose-response curve with a slope of approximately 1 was observed when the logarithm of MNNG-induced transformation frequency was plotted versus the logarithm of MNNG dose. These results are consistent with a one-hit mechanism for induction of preneoplastic variants of RTE cells by MNNG. Similar frequencies and kinetics of induction of preneoplastic variants in other culture systems using diploid cells have been observed, suggesting a common mechanism for this early step in carcinogenesis. The RTE cell system will be useful for mechanistic studies of early as well as late changes in the development of neoplasia by epithelial cells.

Quantitation of the rate of spontaneous generation and carcinogen-induced frequency of anchorage-independent variants of rat tracheal epithelial cells in culture.

The rate of spontaneous generation and the frequency of carcinogen-induced anchorage-independent variants of preneoplastic rat tracheal epithelial (RTE) cells in culture were quantitated. Anchorage-independent variants of different RTE cell lines arose spontaneously by a stochastic process at rates of 0.5 X 10(-4) to 5.4 X 10(-4) variants/cell/generation, as determined by fluctuation analyses. These variants were also induced by the mutagen N-methyl-N'-nitro-N-nitrosoguanidine with a frequency of approximately 10(-3) variants/surviving cell. The rates of spontaneous change and the frequencies of induction are the first reported for epithelial cells and are similar to some, although not all, rates and frequencies of change to anchorage independence for fibroblast-like cells in culture. In addition, these rates and frequencies are similar to those for mutations at some known gene loci. The induced frequency of this late change in neoplastic progression is, however, considerably lower than the frequency of induction of the initial, preneoplastic changes in RTE cells in culture (approximately 3 X 10(-2)/surviving cell). These quantitative determinations are useful in defining the mechanisms of late changes occurring during the progression of RTE cells to the neoplastic state.

Refolding of barnase in the presence of GroE.

The refolding of barnase in the presence of GroEL has been monitored on the millisecond to seconds time scale using stopped-flow kinetics. GroEL binds rapidly and tightly to the denatured enzyme with a second-order rate constant of greater than 1.3 x 10(8) s-1 M-1 and slows down greatly the rate of barnase refolding. However, addition of ever increasing concentrations of GroEL does not prevent barnase refolding completely, as would be expected from mass action if folding of barnase could proceed only in free solution. At saturating concentrations of GroEL, barnase refolds with a half-life of 30 s, compared with 50 ms for refolding of free enzyme. The rate-determining step in the refolding of free barnase is the reaction of a "late" folding intermediate. A mutant of barnase that fold more slowly (Ser-->Ala91), refolds at a correspondingly lower rate when bound to GroEL, suggesting that formation of the fully folded state may be rate limiting for folding on GroEL. For the slow-folding Ser-->Ala91 mutant, the rate-determining refolding step has a half-life of 180 ms. In sequential mixing experiments, a delay was introduced to allow the Ser-->Ala91 mutant to refold for 30 ms before being mixed with GroEL. This reduces by 50% the amount of mutant barnase initially bound by GroEL. As only 11% of this mutant barnase is fully refolded from the late intermediate in 30 ms, there is preferential binding of an earlier refolding state to GroEL. We show by single mixing experiments that binding, not hydrolysis, of ATP reduces the lag in regain of barnase activity seen with GroEL alone. In the presence of high concentrations of ATP and GroEL the rate constant for refolding of barnase approaches that found in their absence, probably because ATP reduces the affinity of GroEL for refolding barnase, such that bound barnase is released and refolds unhindered. The addition of exceedingly small quantities of GroES in the presence of excess GroEL and a moderate amount of ATP also has a marked effect on the barnase refolding rate constant, suggesting that GroES may have higher affinity for the barnase: GroEL complex than for GroEL.

Cooperativity in ATP hydrolysis by GroEL is increased by GroES.

The kinetics of ATP hydrolysis by the 'molecular chaperone' GroEL and the inhibition of this hydrolysis by GroES have been studied in more detail. It is shown that the hydrolysis of ATP by GroEL is cooperative with respect to ATP with a Hill coefficient of 1.86 (+/- 0.13). In the presence of GroES, there is an increase in the degree of cooperativity with a Hill coefficient of 3.01 (+/- 0.18). The observed cooperativity is not due to dissociation of the GroEL oligomer into smaller units but more probably involves structural changes within the GroEL oligomer.

Review of fluvoxamine safety database.

A review of the safety and tolerability of fluvoxamine in worldwide marketing studies involving 24,624 patients, predominantly receiving fluvoxamine treatment in uncontrolled studies in depression, has been conducted. There was a marked preponderance of female patients and patients aged between 30 and 50 years. The majority of patients were treated for 6 weeks, with the most frequent modal total daily dose being 100mg. The greatest proportion of adverse experiences occurring, by COSTART body system, affected the digestive system (24.1%), the nervous system (23.7%), and the body as a whole (15.3%). The only adverse experience with an incidence greater than 10% was nausea (15.7%), with somnolence (6.9%) and asthenia (6.2%) as the next most frequent experiences. Notably, the rates of agitation and anxiety were only 1.4 and 1.3%, respectively. The incidences of adverse experiences increased with age, and were slightly higher in females than males. 15.1% of patients discontinued treatment prematurely as a result of adverse experiences, principally nausea, dizziness, vomiting, somnolence, abdominal pain, and headache. The overall incidence of serious adverse events associated with fluvoxamine treatment was 2.5%, and the incidence of overall suicidality, including suicidal ideation, overdose, and intentional overdose as well as attempted and completed acts of suicide, was remarkably low at 0.8%.

In vitro analysis of multistage carcinogenesis.

Several key events in the multistep process of neoplastic transformation of rat tracheal epithelium (RTE) are described. Whether tracheal epithelium is exposed in vivo to carcinogenic agents or whether primary tracheal epithelial cells are exposed in vitro to carcinogens, initiated stem cells can be detected soon after the exposure by their ability to grow under selective conditions in culture. These initiated stem cells differ fundamentally from normal stem cells in their response to factors normally constraining proliferation and self-renewal. Thus, disruption of inhibitory control mechanisms of stem cell replication appears to be the first event in RTE cell transformation. While the probability of self-renewal (PSR) is clearly increased in initiated stem cells, most of the descendants derived from such stem cells differentiate and become terminal and do not express transformed characteristics. Progression from the first to the second stage of RTE cell transformation, the stage of the immortal growth variant (IGV), is characterized by loss of responsiveness to the growth-restraining effects of retinoic acid. In the third stage of neoplastic transformation, the stage during which neoplastic growth variants (NGV) appear, a growth factor receptor gene is inappropriately expressed in some of the transformants. Thus, it appears that loss of growth-restraining mechanisms may be an early event, and activation of a growth stimulatory mechanism a late event, in neoplastic transformation of RTE cells.

Fluvoxamine. A review of its safety profile in world-wide studies.

Fluvoxamine, a selective serotonin reuptake inhibitor, was studied extensively in 34,587 predominantly depressed patients in 66 studies conducted world-wide. These studies were largely uncontrolled trials representing the use of fluvoxamine by psychiatric and general practice physicians in everyday conditions. The safety data were analyzed according to standardized medical review and data management policies. Approximately 70% of the fluvoxamine population were female and 44% were aged 31-51 years. The modal total daily dose was 100 mg. Safety findings revealed a pharmacological adverse event profile similar to that seen with other serotonin reuptake inhibitors. Nausea was found to be the only common symptom, with an incidence rate of 16%. Approximately 2% of the fluvoxamine population reported at least one serious adverse event (per FDA criteria). Overall suicidality rates of fluvoxamine were found to be low (0.7%). No cases of zimelidine syndrome, bleeding syndrome or Guillain-Barré syndrome were identified. Overall, fluvoxamine was found to be safe and well tolerated suggesting a favorable alternative in the treatment of depression.

Cytotoxicity, genotoxicity and transforming activity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in rat tracheal epithelial cells.

The cytotoxicity, genotoxicity and transforming activity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were studied by the assays of colony-forming efficiency (CFE), micronucleus formation (MN), and cell transformation in rat tracheal epithelial (RTE) cells both in vitro and in vivo. Liver S9, primary hepatocytes and RTE cells from normal and Aroclor-1254 induced rats were compared for bioactivation of NNK using Salmonella mutagenesis as the endpoint. Results from the in vitro experiments indicated that low concentrations of NNK (0.01-25 micrograms/ml) caused from 15% to greater than 100% increases in CFE of RTE cells. At high concentrations (100-200 micrograms/ml), NNK was significantly toxic to RTE cells. NNK treatment in vitro (50-200 micrograms/ml) increased MN frequency as much as 3-fold above background and significantly increased the transformation frequency (TF) in 4/5 (50 micrograms/ml) and 6/8 (100 micrograms/ml) experiments. The in vivo exposure of rats to NNK (150-450 mg/kg, given i.p.) resulted in a 60-85% reduction in CFE and a 3-5-fold increase in MN formation in RTE cells. In vivo treatment with cumulative doses of 150 and 300 mg/kg of NNK produced significant increases in TF of tracheal cells from 3/3 and 2/3 rats, respectively. Without activation, NNK was not mutagenic in Salmonella TA1535. The bioactivation of NNK to a mutagenic metabolite was achieved by incubation of NNK with liver S9 fraction from Aroclor-1254 induced rats or primary hepatocytes from both untreated and Aroclor-1254 pretreated rats. RTE cells did not produce sufficient quantities of mutagenic NNK metabolites to be detected by the Salmonella assay.

Regulation of transformation frequency by exogenous and endogenous growth factors in rat tracheal epithelial cells.

The purpose of our studies was to re-evaluate the rat tracheal epithelial (RTE) transformation system and to identify critical variables that affect the development of enhanced growth variants (EGV). The enhanced growth variant colony, which is a preneoplastic cell variant, is the quantifiable transformation endpoint in RTE cultures. Using a standard protocol the frequency of EGV colony formation was shown to be inversely related to the number of clonogenic cells (CFU) seeded per dish in control cultures as well as in cultures treated with the transforming agent 6-nitrochrysene (6-NC). Experiments showed that the major mechanisms that underlie the CFU density-dependent inhibition of EGV colony formation are depletion of growth factors from and accumulation of autocrine TGF-beta in the media. Thus the cells themselves are creating the selection environment, which allows only the EGVs to survive. The effects of agents such as 6-NC, which increase the frequency of EGV colony formation, are to induce a cellular phenotype that is less susceptible to the selection environment. We showed that TGF-beta-neutralizing antibodies added to the selection media significantly increased EGV colony formation in control cultures but not in 6-NC-exposed cultures. In addition we demonstrated that the development of EGV colonies is much less susceptible to inhibition by (exogenous) TGF-beta in 6-NC-exposed than in control cultures. Thus spontaneous and 6-NC EGV colony formation are distinguishable based on TGF-beta sensitivity. To conduct quantitative cell transformation experiments with RTE cells it is essential that the number of surviving CFU per dish is the same in control and treated cultures. Under the conditions used in the studies described here, 350-500 CFU per culture was found to be the optimum CFU density. Besides 6-NC, agents that have been shown to increase EGV colony frequency under conditions similar to those described here are nitrosamines, NNK, nickel compounds and X-rays.

The effect of sodium selenite on cell proliferation and transformation of primary rat tracheal epithelial cells.

The effects of sodium selenite (Na2SeO3) on cell proliferation and the development of preneoplastic transformed variants were studied in primary cultures of rat tracheal epithelial cells. Results revealed a biphasic effect of Na2SeO3 on cell proliferation: at concentrations between 6 x 10(-8) and 6 x 10(-6) M, it stimulated and at concentrations of approximately 2 x 10(-5) and above it inhibited cell proliferation (presumably due to toxicity). Nontoxic concentrations of Na2SeO3 (6 x 10(-8) -6 x 10(-7) M) significantly reduced the spontaneous transformation frequency. Transformation induced by the tobacco-specific nitrosamine 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was effectively inhibited by nontoxic as well as toxic concentrations of Na2SeO3. Treatment of cultures with Na2SeO3 after cessation of NNK exposure, i.e. during the selection period, also significantly reduced the transformation frequency. These experiments show that the inhibition of transformation by Na2SeO3 is not the result of an antiproliferative effect. They further indicate that the inhibitory effect occurs even when the chemical treatment occurs during the 'postinitiation' phase. Thus the inhibition of transformation by Na2SeO3 cannot solely be explained by its effects on drug metabolism.

Asparagine-344 is a key residue for ligand binding in keratinocyte growth factor receptor.

The membrane proximal, immunoglobulin- (Ig-) like domain 3 of KGFR shows significant sequence similarity to the Ig light chain variable (V) domain. According to our model, based on this similarity, the F-G loop in KGFR corresponds to the complementarity determining region (CDR) 3 of the Ig V domain. The F-G loop in the membrane proximal domain of the keratinocyte growth factor receptor has previously been shown to participate in determining the FGF ligand binding specificity of KGFR [Gray, T. E., Eisenstein, M., Shimon, T., Givol, D., & Yayon, A. (1995) Biochemistry 34, 10325-10333]. Here, we report the effects of additional mutations in this F-G loop. Both a single mutant KGFR Q348-->I and a double mutant KGFR Q348-->I, Q351-->H are found to have relatively mild effects on ligand binding, as was previously found for three other F-G loop mutant receptors. In contrast, a single mutation N344-->A in the F-G loop of KGFR is sufficient to abolish essentially all affinity of this receptor for its primary ligand KGF, while some affinity for aFGF is retained. Asparagine-344 is, therefore, essential for ligand binding by KGFR. We discuss the likelihood of this effect being due to global or local structural changes or to the removal of a specific interaction with the ligand, in relation to various known and model structures. Taking into account the mild effects of other mutations in the region and various other considerations, we tend to favor the idea that asparagine-344 is a key residue in determining the local conformation of the F-G loop.

Contrasting responses of normal and transformed rat tracheal epithelial cells to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate.

The data presented here are part of an ongoing effort to examine the response of rat tracheal epithelium to tumor promoting agents and to elucidate the mechanisms of tumor promotion in that epithelial tissue (see Steele, this volume). Previous studies indicated that airway epithelium is responsive to the tumor promoter TPA and that TPA can promote the tumor response in rat tracheal epithelium But what are the mechanisms involved? We have divided this question into two main elements: 1) Which stages of neoplastic development are affected by TPA, i.e., which preneoplastic cell populations are targets for TPA action resulting in the acceleration and enhancement of the process of neoplastic development? 2) What effects does TPA have on various preneoplastic cell populations and how do such effects result in promotion? The experiments discussed here relate to the second part of the question. They suggested that TPA elicits a marked cytotoxic response in stably transformed RTE cell variants (see Fig. 1). These preneoplastic cell variants are clearly different from untransformed RTE cells which are triggered into cell cycle as indicated by an increase in CFE. This difference between normal and transformed cells is of considerable interest in itself since it points to a fundamental, biochemical alteration in the transformed cells. Evidence exists that transformed RTE cell lines have TPA receptors and that at least some of the responses elicited by TPA exposure, such as the induction of ornithine decarboxylase activity, are receptor-mediated. Whether the cytotoxic response elicited by TPA is receptor-mediated is presently not known.(ABSTRACT TRUNCATED AT 250 WORDS)

Mucociliary differentiation of serially passaged normal human tracheobronchial epithelial cells.

The goal of our studies was to establish procedures for subculturing normal human tracheobronchial epithelial (NHTBE) cells without compromising their ability to differentiate into mucous and ciliated cells (i.e., differentiation competence) and to study the regulation of airway secretions by epidermal growth factor (EGF) and retinoic acid (RA). Primary NHTBE cells were obtained from a commercial source and subcultured repeatedly in serum-free medium on plastic tissue culture dishes. The subcultured cells were tested after every passage for differentiation competence in air-liquid interface (ALI) cultures. The apical secretions of cultured NHTBE cells were characterized by immunoblotting, Western blotting, or enzyme-linked immunosorbent assay using a variety of antibodies. They contained mucin-like materials as well as lysozyme, lactoferrin, and secretory leukocyte protease inhibitor (SLPI). We found that an EGF concentration of 25 ng/ml, which is commonly used in airway cell cultures, adversely affected growth, mucin production, and morphology of ALI cultures and that RA was essential for mucociliary differentiation. Without RA, the epithelium became squamous and mucin secretions decreased 300- to 900-fold. In contrast, secretion of lysozyme, lactoferrin, and SLPI was significantly increased in RA-depleted cultures. Cells of passage 2 (P-2) through P-4 remained competent to differentiate into mucous and ciliated cells when grown in ALI cultures. However, mucin secretion and ciliagenesis decreased in P-3 and P-4 cell cultures and P-3 but not P-4 cell cultures exhibited bioelectric properties characteristic of airway epithelium. We concluded that P-2 and P-3 NHTBE cell cultures retain many important features of normal airway epithelium. This enables one to conduct many studies of airway cell biology with a greatly expanded (6,000-fold) cell pool.

Enhanced growth potential of cultured rabbit tracheal epithelial cells following exposure to N-methyl-N'-nitro-N-nitrosoguanidine.

To establish a standardized model for the transformation of rabbit airway epithelial cells, we attempted to transform rabbit tracheal epithelial (RbTE) cells in culture with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). RbTE cells, harvested by enzymatic digestion from male New Zealand white rabbits, were plated onto feeder layers of irradiated 3T3 cells. Control cells proliferated exponentially during the 2nd week of culture and reached the plateau phase by the 3rd week. Cells exposed to MNNG (0.1 microgram/ml) proliferated in a fashion similar to the control cells, except that there was some delay before proliferation began. The clonogenic activity of RbTE cells rapidly decreased in parallel with the increase in cell population equally in the control and MNNG groups. During the late plateau phase, cells exposed to MNNG regained clonogenic activity, and this compartment size expanded with time, whereas the clonogenic activity in control cultures remained below the detectable level. In RbTE cell cultures exposed three times to 0.1 microgram/ml MNNG, large, persistent and proliferating colonies emerged at a frequency of 1-3 x 10(-2) among the surviving clones, whereas all the control cultures eventually became senescent. The MNNG-induced alteration in the growth potential of RbTE cells, i.e., the extended lifespan, and the maintenance and even expansion of clonogenic activity, was similar to that of transformed rat tracheal epithelial cells. However, no immortal cell line could be established from these growth-altered RbTE cells. We therefore concluded that the growth-altered RbTE cells were partially transformed.

Refolding of barnase mutants and pro-barnase in the presence and absence of GroEL.

Three mutants of barnase and a pro-barnase variant, which have a variety of different physical properties but the same overall protein structure, were analysed for their folding in the presence of the molecular chaperone GroEL. Mutants were chosen on the basis that changes in their refolding rate constants in solution are not correlated with the changes in their stability. All barnase variants fold considerably more slowly when bound to GroEL. However, barnase refolding on GroEL parallels that in solution: there is a linear relationship between the refolding rate constants, obtained for wild-type and all mutants of barnase, in the presence and absence of GroEL. Barnase is synthesized in vivo with a 13 amino acid pro-sequence attached to the N-terminus. The pro-sequence of pro-barnase is shown by NMR spectroscopy to be devoid of defined structure. The presence of this pro-sequence has no effect on the overall refolding rate constant or the activity of barnase. In the presence of GroEL, the refolding of pro-barnase is retarded relatively more strongly than that of wild-type and the mutant barnase proteins, suggesting that the pro-sequence provides additional binding sites for the chaperone.

Characterization of a third transforming growth factor beta 1 transcript in rat tracheal epithelial cells.

It has been previously reported (R. W. Steigerwalt et al., Mol. Carcinog., 5:32-40, 1992) that primary cultures of rat tracheal epithelial (RTE) cells and immortalized RTE cell lines produce three mRNA transcripts [2.5, 1.9, 1.4 kilobases (kb)] which hybridize to a murine transforming growth factor beta 1 (TGF-beta 1) complementary DNA probe. In this report, we show that the 1.9- and 1.4-kb transcripts are not detectable by Northern analysis of resting adult trachea but are induced in regenerating tracheal grafts and tumors formed from transformed RTE cells. Northern analysis of the TGF-beta 1 transcripts with subclones of the murine complementary DNA demonstrate that the 1.4-kb transcript lacks much of the 5' untranslated region (UTR). RNase protection analysis was used to map the transcriptional start site of the 1.4-kb transcript to within 30-40 base pairs of the first ATG codon. No differences in the coding or 3' UTR were detected between the 1.4-kb and the 2.5-kb transcripts. Although RTE cells produce a 1.9-kb TGF-beta 1 mRNA, we were unable to detect a previously reported unique 3' UTR, which we found to be almost identical to a rat mitochondrial ATPase sequence. Because the 1.4-kb transcript is missing most of the long GC-rich 5' UTR, it may be translated at a different rate than the 2.5- and 1.9-kb transcripts, or it may code for an intracellular form of TGF-beta 1. The 1.4-kb transcript has been observed under several conditions of injury or stress and, therefore, may be an important component of the TGF-beta 1 response to these conditions.

Arachidonic acid metabolism in normal and transformed rat tracheal epithelial cells and its possible role in the regulation of cell proliferation.

The objectives of our investigations were to characterize the profile of arachidonic acid metabolites produced by cultured rat tracheal epithelial cells, and to determine whether or not transformation of these cells causes major qualitative or quantitative changes in arachidonic acid metabolism and whether arachidonic acid metabolites play an important role in the regulation of proliferation of rat tracheal cells. Our studies showed that prostaglandin E2 was the only major prostanoid produced by normal and transformed rat tracheal epithelial cells. When stimulated with calcium ionophore A23187, 12-O-tetradecanoylphorbol 13-acetate, arachidonic acid, or serum, the cultures produced small amounts of thromboxane B2, prostaglandin F2 alpha, and hydroxyeicosatetraenoic acid(s) in addition to prostaglandin E2. Mitogenesis studies showed that none of the peptide growth factors tested stimulated either prostaglandin E2 production or DNA synthesis. Fetal bovine serum, on the other hand, stimulated both. 12-O-Tetradecanoylphorbol 13-acetate and arachidonic acid stimulated prostaglandin E2 production but caused no increase in DNA synthesis. Dexamethasone and indomethacin, inhibitors of phospholipase A2 and cyclooxygenase, respectively, significantly inhibited prostaglandin E2 production at concentrations as low as 10(-8) and 10(-9) M but did not inhibit DNA synthesis. It is concluded (1) that prostaglandin E2 is the major arachidonic acid metabolite of rat tracheal epithelial cells, (2) that transformation does not significantly alter arachidonic acid metabolism in these cells, and (3) that neither prostaglandin E2 nor other arachidonic acid metabolites play a significant role in mitogenic stimulation of rat tracheal epithelial cells.

Safety database on fluvoxamine: analysis and report.

A review was conducted of the safety and tolerability of fluvoxamine in 54 worldwide marketing studies that enrolled 24,624 patients, the majority of whom were treated with fluvoxamine in uncontrolled studies in depression. In accordance with the general epidemiologic distribution of depressive disorder, female patients and patients aged between 30 and 50 years predominated. The majority of patients were treated for 6 weeks, the most frequent, or modal, total daily dose being 100 mg. Overall, 57.4% of the patients exposed to fluvoxamine did not have any adverse experiences. The greatest proportion of adverse experiences, as defined using COSTART body systems, affected the digestive system (24.1%), the nervous system (23.7%), and the body as a whole (15.3%). The only adverse experience with an incidence greater than 10% was nausea (15.7%); somnolence (6.9%) and asthenia (6.2%) were the next most frequent adverse experiences. Notably, the rates of agitation and anxiety were only 1.4% and 1.3%, respectively. The incidences of adverse experiences generally increased with age and were slightly higher in females than in males. In total, 15.1% of patients discontinued treatment prematurely as a result of adverse experiences, principally nausea, dizziness, vomiting, somnolence, abdominal pain, and headache. The overall incidence of serious adverse events in association with fluvoxamine treatment was 2.5% when U.S. Food and Drug Administration criteria and the most conservative approach, without causality judgments, were used.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular modeling based mutagenesis defines ligand binding and specificity determining regions of fibroblast growth factor receptors.

The fibroblast growth factor receptor 2 (FGFR2) and the keratinocyte growth factor receptor (KGFR) have different ligand binding specificities despite differing only in the second half of their immunoglobulin-like (Ig-like) domain III. Three-dimensional model structures were generated for domain III on the basis of variable (V) Ig domains. The region that differs between the two receptors is predicted to include two loops: one connects beta-strands F-G and is analogous to the complementarity determining region 3 (CDR3) of immunoglobulins; the other connects beta-strands D-E. These regions were targeted for mutagenesis. Single mutations in the F-G loop were found to only slightly alter ligand binding, whereas a double mutant, KGFR Y345-->S,Q348-->I, acquired significant affinity for bFGF. Notably, the affinity of this double mutant KGFR for KGF and aFGF was essentially unaltered. A mutant FGFR2, in which the D-E beta-hairpin (T319TDKEI) is replaced with the KGFR D-E beta-hairpin (S319SNA), has 9-fold reduced affinity for bFGF. These results demonstrate that the F-G or CDR3 analogous loop in FGFRs plays a key role in determining ligand binding and specificity. In addition, however, the protein loop connecting beta-strands D and E may also be involved in ligand binding. Several point mutations in FGFR2, shown recently to give rise to multiple inherited skeletal defects, are localized according to our models to the F-G or D-E loops of domain III. Our results strongly suggest that these naturally occurring mutations specifically alter ligand binding by FGFR2.

Site-directed mutagenesis reveals transition-state stabilization as a general catalytic mechanism for aminoacyl-tRNA synthetases.

Some aminoacyl-tRNA synthetases of almost negligible homology do have a small region of similarity around four-residue sequence His-Ile(or Leu or Met)-Gly-His(or Asn), the HIGH sequence. The first histidine in this sequence in the tyrosyl-tRNA synthetase, His-45, has been shown to form part of a binding site for the gamma-phosphate of ATP in the transition state for the reaction as does Thr-40. Residue His-56 in the valyl-tRNA synthetase begins a HIGH sequence, and there is a threonine at position 52, one position closer to the histidine than in the tyrosyl-tRNA synthetase. The mutants Thr----Ala-52 and His----Asn-56 have been made and their complete free energy profiles for the formation of valyl adenylate determined. Difference energy diagrams have been constructed by comparison with the reaction of wild-type enzyme. The difference energy profiles are very similar to those for the mutants Thr----Ala-40 and His----Asn-45 of the tyrosyl-tRNA synthetase. Thr-52 and His-56 of the valyl-tRNA synthetase contribute little binding energy to valine, ATP, and Val-AMP. Instead, the wild-type enzyme binds the transition state and pyrophosphate some 6 kcal/mol more tightly than do the mutants. Preferential transition-state stabilization is thus an important component of catalysis by the valyl-tRNA synthetase. Further, by analogy to the tyrosyl-tRNA synthetase, the valyl-tRNA synthetase has a binding site for the gamma-phosphate of ATP in the transition state, and this is likely to be a general feature of aminoacyl-tRNA synthetases that have a HIGH region.