Relationship between the CYP2D6 genotype and the steady-state plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine

The relationship between the cytochrome P450 (CYP) 2D6 genotype and the steady-state plasma concentrations (Css) of trazodone and its active metabolite m-chlorophenylpiperazine (mCPP) was studied in 54 depressed Japanese patients receiving trazodone 150 mg at bedtime. By use of allele-specific PCR analysis, the wild type allele, three mutated alleles causing absent enzyme activity (CYP2D6A, CYP2D6B and CYP2D6D) and one mutated allele causing decreased enzyme activity (CYPZD6 Ch) were identified. The means (ranges) of the Css of trazodone, corrected to the median body weight in 17 cases with no mutated allele, 27 cases with one mutated allele and 10 cases with two mutated alleles, were 556 (281-1115), 643 (302-1362) and 671 (234-1418) ng/ml, respectively, while the values of mCPP were 60 (35-121), 65 (33-99) and 58 (38-112) ng/ml, respectively. Neither the Css of trazodone (F = 0.80, P = 0.45) nor that of mCPP (F = 0.49, P = 0.61) significantly differed among the three groups. The present study thus suggests that the CYP2D6 genotype cannot predict the Css of these compounds.

Immortalization of mutant p53-transfected human fibroblasts by treatment with either 4-nitroquinoline 1-oxide or X-rays

The study of in vitro cell transformation is valuable for understanding the multistep carcinogenesis of human cells. The difficulty in inducing neoplastic transformation of human cells by treatment with chemical or physical agents alone is due to the difficulty in immortalizing normal human cells. Thus, the immortalization step is critical for in vitro neoplastic transformation of human cells. We transfected a mutant p53 gene (mp53: codon 273Arg-His) into normal human fibroblasts and obtained two G418-resistant mp53-containing clones. These clones showed an extended life span but ultimately senesced. However, when they were treated with either 4-nitroquinoline 1-oxide or X-rays, they were immortalized. The immortalized cells showed both numerical and structural chromosome abnormalities, but they were not tumorigenic. The expression of mutant but not wild type p53 was detected in the immortalized cells by RT-PCR. Expression of p21, which is located downstream of p53, was remarkably reduced in the immortalized cells, resulting in increased cdk2 and cdc2 kinase activity. However, there was no significant difference between the normal and immortalized human cells in expression of another tumor suppressor gene, p16. These findings indicate that the p53-p21 cascade may play an important role in the immortalization of human cells.

Analysis of the functional domain of the rat liver mitochondrial import receptor Tom20

Tom20 is an outer mitochondrial membrane protein and functions as a component of the import receptor complex for the cytoplasmically synthesized mitochondrial precursor proteins. It consists of the N-terminal membrane-anchor segment, the tetratricopeptide repeat (TPR) motif, a charged amino acids-rich linker segment between the membrane anchor and the TPR motif, and the C-terminal acidic amino acid cluster. To assess the functional significance of these segments in mammalian Tom20, we cloned rat Tom20 and expressed mutant rat Tom20 proteins in Deltatom20 yeast cells and examined their ability to complement the defects of respiration-driven growth and mitochondrial protein import. Tom20N69, a mutant consisting of the membrane anchor and the linker segments, was targeted to mitochondria and complemented the growth and import defects as efficiently as wild-type Tom20, whereas a mutant lacking the linker segment did not. In vitro protein import into mitochondria isolated from the complemented yeast cells revealed that the precursor targeted to yeast Tom70 was efficiently imported into the mitochondria via rat Tom20N69. Thus the linker segment is essential for the function of rat Tom20, whereas the TPR motif and the C-terminal acidic amino acids are not.

Binding of mitochondrial precursor proteins to the cytoplasmic domains of the import receptors Tom70 and Tom20 is determined by cytoplasmic chaperones

We have reconstituted the early steps of precursor targeting to mitochondria in a defined and soluble system consisting of the cytosolic domains of the yeast mitochondrial import receptors Tom20 and Tom70, precursor to bovine adrenal adrenodoxin (which has a cleavable targeting signal) and rat liver cytosolic chaperones hsp70 and mitochondrial import-stimulating factor (MSF). The Tom70 domain only bound the precursor in the presence of MSF, yielding a precursor-MSF-Tom70 complex; ATP hydrolysis by MSF released MSF and generated a precursor-Tom70 complex whose formation was inhibited by an excess of a functional presequence peptide, but not by 150 mM NaCl. In the presence of the Tom20 domain, ATP caused transfer of the precursor from the precursor-MSF-Tom70 complex to Tom20. The Tom20 domain alone only bound the precursor in the presence of hsp70; hsp70 itself was not incorporated into the resulting complex. Formation of the Tom20-precursor complex was inhibited by excess presequence peptide or by 150 mM NaCl. Similar results were obtained with the ADP/ATP carrier and porin precursors, which both lack a cleaved targeting signal. Correct targeting of a precursor to mitochondrial import receptors thus requires cytosolic chaperones, irrespective of the presence or absence of a cleavable presequence.

Increased plasma concentrations of bromperidol and its reduced metabolite with levomepromazine, but not with thioridazine

Bromperidol is a close structural analog of haloperidol. The authors studied the effects of levomepromazine and thioridazine, which are frequently added to other neuroleptics as sedatives, on plasma concentrations of bromperidol and its reduced metabolite. The subjects were 26 inpatients with schizophrenia receiving bromperidol, 12 to 24 mg/day, for 1 to 19 weeks. In 10 cases, 50 mg levomepromazine per day and in nine cases, 50 mg thioridazine per day were coadministered for 1 week. In seven cases, both drugs were coadministered with > or = 2-week intervals. Plasma concentrations of bromperidol and reduced bromperidol were measured by a high-performance liquid chromatographic method. Levomepromazine (n = 17) significantly (p < 0.001) increased plasma concentrations of bromperidol (7.3 +/- 4.1 versus 10.2 +/- 4.8 ng/ml) and reduced bromperidol (1.8 +/- 1.4 versus 4.5 +/- 3.3 ng/ml). Thioridazine (n = 16) did not significantly change plasma concentrations of bromperidol (9.1 +/- 5.7 versus 8.6 +/- 5.5 ng/ml), while those of reduced bromperidol could not be measured because of interfering peaks. The current study suggests that levomepromazine, but not thioridazine, increases plasma concentrations of bromperidol and reduced bromperidol by inhibiting the metabolism of these compounds.

Evidence for proton transfer from Glu-46 to the chromophore during the photocycle of photoactive yellow protein

Photoactive yellow protein (PYP) belongs to the novel group of eubacterial photoreceptor proteins. To fully understand its light signal transduction mechanisms, elucidation of the intramolecular pathway of the internal proton is indispensable because it closely correlates with the changes in the hydrogen-bonding network, which is likely to induce the conformational changes. For this purpose, the vibrational modes of PYP and its photoproduct were studied by Fourier transform infrared spectroscopy at -40 degrees C. The vibrational modes characteristic for the anionic p-coumaryl chromophore (Kim, M., Mathies, R. A., Hoff, W. D., and Hellingwerf, K. J. (1995) Biochemistry 34, 12669-12672) were observed at 1482, 1437, and 1163 cm-1 for PYP. However, the bands corresponding to these modes were not observed for PYPM, the blue-shifted intermediate, but the 1175 cm-1 band characteristic of the neutral p-coumaryl chromophore was observed, indicating that the phenolic oxygen of the chromophore is protonated in PYPM. A 1736 cm-1 band was observed for PYP, but the corresponding band for PYPM was not. Because it disappeared in the Glu-46 --> Gln mutant of PYP, this band was assigned to the C=O stretching mode of the COOH group of Glu-46. These results strongly suggest that the proton at Glu-46 is transferred to the chromophore during the photoconversion from PYP to PYPM.

Functional expression and site-directed mutagenesis of photoactive yellow protein

The gene encoding photoactive yellow protein (PYP) was isolated from Ectothiorhodospira halophila, and a high-level expression system for PYP was constructed in Escherichia coli. The molecular weight and the absorption spectrum of PYP expressed in E. coli were identical with those of the native PYP isolated from E. halophila. The amino acid residues which might interact with the chromophore (Tyr42, Glu46, Thr50, Arg52, and Cys69) were mutated by site-directed mutagenesis and the absorption spectra of these mutants were examined to study the chromophore/protein interaction in PYP. The former three substitutions (Y42F, E46Q, and T50V) brought about red-shifts of the absorption spectra, but the substitution of Arg52 (R52Q) brought about no change and that of Cys69 (C69S) led to no formation of pigments. These results suggest that Tyr42, Glu46, and Thr50 strongly interact with the chromophore, while Arg52 does not contribute the color tuning of PYP.

No effect of the anticholinergic drugs trihexyphenidyl and biperiden on the plasma concentrations of bromperidol and its reduced metabolite

Effects of the anticholinergic drugs trihexyphenidyl and biperiden on plasma concentrations of bromperidol and its reduced metabolite were studied. Subjects comprised 20 schizophrenic inpatients taking bromperidol, 6-18 mg/ day for 1-9 weeks. Patients were randomly allocated to one of two treatment sequences: trihexyphenidyl-biperiden (n = 12) or biperiden-trihexyphenidyl (n = 8). Each sequence consisted of two 2-week phases, with no washout period between the two phases. The daily dose of trihexyphenidyl was 8 mg and that of biperiden 6 mg. Plasma concentrations of bromperidol and reduced bromperidol were measured using high-performance liquid chromatography (HPLC). There was no significant difference in plasma bromperidol or reduced bromperidol concentrations among baseline, trihexyphenidyl and biperiden phases: 7.3 +/- 3.7 versus 7.2 +/- 4.1 versus 7.0 +/- 4.3 ng/ml and 2.0 +/- 2.1 versus 2.2 +/- 2.1 versus 1.9 +/- 2.0 ng/ml, respectively. The present study thus suggests that neither trihexyphenidyl nor biperiden affects plasma concentrations of bromperidol and its reduced metabolite.

Metaxin is a component of a preprotein import complex in the outer membrane of the mammalian mitochondrion

Metaxin, a novel gene located between the glucocerebrosidase and thrombospondin 3 genes in the mouse, is essential for survival of the postimplantation mouse embryo. In this study, the subcellular location, domain structure, and biochemical function of metaxin were investigated. Anti-recombinant metaxin antibodies recognized 35- and 70-kDa proteins in mitochondria from various tissues; the 35-kDa protein is consistent in size with the predicted translation product of metaxin cDNA. When metaxin cDNA was transfected into COS cells, immunofluorescence staining demonstrated that the protein is located in mitochondria. Metaxin contains a putative mitochondrial outer membrane signal anchor domain at its C terminus, and a truncated form of metaxin lacking this signal anchor domain had a reduced association with mitochondria. In addition, metaxin was highly susceptible to proteases in intact mitochondria. We therefore conclude that metaxin is a mitochondrial protein that extends into the cytosol while anchored into the outer membrane at its C terminus. In its N-terminal region, metaxin shows significant sequence identity to Tom37, a component of the outer membrane portion of the mitochondrial preprotein translocation apparatus in Saccharomyces cerevisiae, but important structural differences, including apparently different mechanisms of targeting to membranes, also exist between the two proteins. Given the similar subcellular locations of metaxin and Tom37, the possible role of metaxin in mitochondrial preprotein import was investigated. Antibodies against metaxin, when preincubated with mitochondria, partially inhibited the uptake of radiolabeled preadrenodoxin into mitochondria. Metaxin is therefore the second mammalian component of the protein translocation apparatus of the mitochondrial outer membrane to be characterized at the molecular level and the first for which an inherited mutation has been described. The early embryonic lethal phenotype of mice lacking metaxin demonstrates that efficient import of proteins into mitochondria is crucial for cellular survival. The characterization of metaxin provides an opportunity to elucidate similarities and possible differences in the mechanisms of protein import between fungi and mammals and in the phenotypes of fungi and mammals lacking mitochondrial import receptors.

Increases in plasma concentration of m-chlorophenylpiperazine, but not trazodone, with low-dose haloperidol

Our previous study suggested that cytochrome P4502D6 (CYP2D6) is involved in the metabolism of trazodone and its active metabolite, m-chlorophenylpiperazine (m-CPP). The purpose of this study was to examine the degrees of increase in plasma concentrations of trazodone and m-CPP induced by haloperidol, which is an inhibitor of CYP2D6. The subjects were nine depressed inpatients receiving trazodone at bedtime (150 mg in seven patients and 300 mg in two) for 2-19 weeks. Haloperidol at 4 mg/day was coadministered for 1 week, and blood samplings were taken before and after the coadministration. Contrary to our expectation, haloperidol did not significantly increase the mean plasma trazodone concentration (810 +/- 382 vs. 856 +/- 357 ng/ml). However, haloperidol significantly increased (p < 0.01) the mean plasma m-CPP concentration (78 +/- 31 vs. 92 +/- 34 ng/ml).

Transformation of normal human fibroblasts into immortalized cells with the mutant p53 gene and X-rays

In vitro cell transformation is a valuable approach for studying the mechanisms of multistep carcinogenesis of human cells. Since immortalization is an essential step for in vitro neoplastic transformation of human cells, this study addresses the question of whether mutant p53 contributes to the immortalization process of human cells. The mutant p53 gene (mp53: codon273Arg-His) was introduced into normal human fibroblasts (OUMS-24 line) and a G418-resistant clone, OUMS-24/P6 line, was obtained. This clone showed an extended life span and chromosome abnormalities, but senesced at the 79th population doubling level (PDL). When these cells were subjected to intermittent X-ray treatment, they became an immortalized cell line (OUMS-24/P6X). Although these immortalized cells showed chromosome abnormalities, they were not tumorigenic. On the other hand, normal OUMS-24 cells into which mp53 had not been introduced were not immortalized by the same X-ray treatment. These results indicate that introduction and expression of mp53 alone were not sufficient for immortalization of human cells, and that mutations of the remaining wild-type p53 or other genes may have been necessary for immortalization. In fact, no expression of the wild-type p53 was detected in the immortalized cells by RT-PCR. Expression of p21, which is located downstream of p53, was remarkably reduced in the immortalized cells, resulting in an increase in cdk2 and cdc2 kinase activity. These findings indicate that the p53-p21 cascade may play some role in the immortalization of human cells. On the other hand, there was no significant difference in expression of proteins such as Rb, p16, cdk4, cdk6, cyclin A and cyclin D1 between the normal and immortalized human fibroblasts.

Identification and functional characterization of yeast zeta-COP

Coatomer, the cytosolic protein complex, consists of seven subunits (alpha-, beta-, beta'-, gamma-, delta-, epsilon-, and zeta-COP) and is involved in vesicle trafficking early in the secretory pathway in collaboration with a 20 kDa GTP-binding protein (ARF). In the present study, we have identified a yeast gene which encodes a protein having 39% amino acid sequence identity with bovine zeta-COP. This gene (YZC1 for Yeast Zeta COP) is essential for vegetative growth and the growth defect of delta yzc1 cells was restored by bovine zeta-COP cDNA. We isolated a temperature-sensitive mutant of YZC1 (yzc1ts) and examined its capacity for both the ER-to-Golgi transport and the double lysine motif (KKXX)-mediated retrograde transport from Golgi to ER. At non-permissive temperature, the yzc1ts cells exhibited a weak defect in the anterograde transport, but a strong defect in the retrograde vesicle transport. We conclude that Yzc1p is a yeast homologue of mammalian zeta-COP and participates mainly in the Golgi-to-ER retrograde transport.

Plasma concentrations of trazodone and m-chlorophenylpiperazine at steady state can be predicted from those after an initial dose of trazodone

1. The authors studied the correlations between plasma concentrations of trazodone and mCPP at steady state and those after an initial dose of trazodone. 2. Fifteen depressed patients received trazodone 150 mg at bedtime for 3 weeks, and blood samplings were taken 12 h after the initial dose and 12 h after the last dose at each week. Plasma concentrations of trazodone and mCPP were measured by high-performance liquid chromatography. 3. Plasma concentration of mCPP, but not trazodone, was significantly higher at each week than after initial dosing. 4. For both trazodone and mCPP, significant linear relationships were found between plasma concentration after initial dosing and the average of 3 weeks' plasma concentrations. 5. The present study thus suggests that plasma concentrations of trazodone and mCPP at steady state can be predicted from those after an initial dose of trazodone.

Interaction between carbamazepine and bromperidol

OBJECTIVE

The interaction between carbamazepine and bromperidol was studied in 13 schizophrenic inpatients.

METHODS

Before carbamazepine addition, the subjects were taking bromperidol 12-24 mg.day-1 for 1-20 weeks. Carbamazepine 400 mg.day-1 was coadministered for 4 weeks, and blood samplings were performed before carbamazepine addition and at weekly intervals after the addition. Plasma concentrations of bromperidol and its reduced metabolite were measured by high-performance liquid chromatography.

RESULTS

Carbamazepine significantly decreased plasma concentrations of both bromperidol and reduced bromperidol for all weeks. On average, the plasma concentrations of bromperidol and reduced bromperidol at 4 weeks were 37% and 23% of the corresponding precarbamazepine values. Despite these decreases in plasma concentration, the Clinical Global Impression scores decreased slightly but significantly after carbamazepine addition.

CONCLUSION

The present study suggests that carbamazepine decreases plasma concentrations of bromperidol and its reduced metabolite by inducing the metabolism of these compounds. Nevertheless, adjunctive carbamazepine may be useful for schizophrenic patients treated with bromperidol.

Cytosolic factors in mitochondrial protein import

In vitro import studies have confirmed the participation of cytosolic protein factors in the import of various precursor proteins into mitochondria. The requirement for extramitochondrial adenosine triphosphate for the import of a group of precursor proteins seems to be correlated with the chaperone activity of the cytosolic protein factors. One of the cytosolic protein factors is hsp70, which generally recognizes and binds unfolded proteins in the cytoplasm. Hsp70 keeps the newly synthesized mitochondrial precursor proteins in import-competent unfolded conformations. Another cytosolic protein factor that has been characterized is mitochondrial import stimulation factor (MSF), which seems to be specific to mitochondrial precursor proteins. MSF recognizes the mitochondrial precursor proteins, forms a complex with them and targets them to the receptors on the outer surface of mitochondria.

Hallucinations after a therapeutic dose of benzodiazepine hypnotics with co-administration of erythromycin

A case of repetitive hallucinations during treatment with a therapeutic dosage of triazolam (0.25 mg/day) and nitrazepam (5 mg/day) is presented. The patient suffered from acute pneumonia and chronic renal failure. Such non-psychotic symptoms as anxiety, tremor and depressed feeling were observed initially. However, after co-administration of erythromycin (600 mg/day), visual hallucinations and abnormal bodily sensations developed repeatedly after each administration of triazolam or nitrazepam. This report suggests that benzodiazepine hypnotics even at a therapeutic dosage with co-administration of erythromycin causes serious psychotic symptoms in vulnerable patients with physical complications.

Possible inhibitory effect of diazepam on the metabolism of zotepine, an antipsychotic drug

Effects of smoking and cytochrome P450 2C19 (CYP2C19) status on the single dose kinetics of zotepine and pharmacokinetic interaction between zotepine and diazepam were investigated. In 14 healthy volunteers, the pharmacokinetics of zotepine after a single oral 25 mg dose were compared between eight smokers and six non-smokers, or between seven extensive metabolizers (EMs) and seven poor metabolizers (PMs) of S-mephenytoin. There was no significant difference in any pharmacokinetic parameters between smokers and non-smokers, or between the EM and PM groups. In 17 patients treated with zotepine 80-340 mg/day, intra-individual changes in plasma concentrations of zotepine caused by coadministration of diazepam 10 mg/day for 2 weeks were examined. Plasma concentrations of zotepine were significantly increased after coadministration of diazepam (P < 0.05). Consequently, it is suggested that neither smoking nor CYP2C19 status affects the metabolism of zotepine. The elevation in plasma concentrations of zotepine after coadministration of diazepam may be a result of competitive inhibition of zotepine metabolism by diazepam via other isoenzyme than CYP2C19, e.g., CYP3A4.

No interaction between desipramine and bromperidol

1. The authors studied the effects of coadministration of desipramine, which is a substrate of CYP2D6, on plasma concentrations of bromperidol and its reduced metabolite (reduced bromperidol). Clinical changes were also evaluated by the CGI and UKU. 2. The subjects were 13 schizophrenic inpatients receiving bromperidol 12.24 mg/day for 1.20 weeks. Desipramine 50 mg/day was coadministered for 1 week, and blood samplings and clinical ratings were performed before and after the coadministration. 3. Plasma concentrations of bromperidol and reduced bromperidol were measured by a HPLC method. 4. Desipramine coadministration did not affect plasma concentration of bromperidol (9.6 +/- 4.5 vs. 9.6 +/- 2.8 ng/ml) nor that of reduced bromperidol (2.8 +/- 2.5 vs. 2.8 +/- 2.1 ng/ml). 5. There was no significant change in the CGI scores nor UKU scores after desipramine coadministration. 6. The present study thus suggests that there is no interaction between desipramine and bromperidol.

Two-dimensional electrophoretic studies on down-regulated intracellular transferrin in human fibroblasts immortalized by treatment with either 4-nitroquinoline 1-oxide or 60Co gamma rays

The immortalization of human cells is an important early step of carcinogenesis. To investigate the mechanisms of immortalization, we established three immortalized human fibroblast cell lines by treatment with either 4-nitroquinoline 1-oxide (4NQO) or 60Co gama rays. Using two-dimensional gel electrophoresis (2-D PAGE), we identified proteins which are down-regulated in these immortalization cell lines. Their isoelectric points ranged between 5.5 and 6.3, and their molecular masses were approximately 80 kDa. The proteins were also decreased in another human fibroblast cell line immortalized with simian virus 40 (SV40) and two human cervical cell lines. The proteins were present in a cytoskeletal fraction, reacted with anti-transferrin antibody and some of them were phosphorylated. The proteins were identified as transferrin. Although the 2-D PAGE patterns of our proteins and serum transferrin of different origin were distinct from each other, their isoelectric points and molecular weights were similar. We implicate some functions of intracellular transferrin, other than an iron transporter, in immortalization of human cells and discuss a new aspect of transferrin metabolism in the cells.

Protein import into mammalian mitochondria. Characterization of the intermediates along the import pathway of the precursor into the matrix

We have characterized several intermediates in the mitochondrial import stimulation factor (MSF)-dependent import into mammalian mitochondria of a matrix-targeted precursor, preadrenodoxin (pAd). In the first step, pAd docks onto the 37-kDa protein of the outer membrane (OM37) as a complex with MSF (stage I intermediate). It is then transferred to the import pore of OM in the presence of ATP, but in the absence of Deltapsi across the inner membrane (IM), to form stage II intermediate. Depletion of matrix ATP in the presence of both extramitochondrial ATP and Deltapsi induces accumulation of stage III intermediate, which is a mixture of the precursor with different intramitochondrial localizations: the precursor whose presequence had crossed either OM (IIIa) or both OM and IM (IIIb), but with a bulk portion remaining exposed to the cytosol and the precursor whose presequence had crossed both membranes, but with a residual portion staying within the intermembrane space (IIIc). These intermediates are on the correct import pathway and are characteristic in their protease accessibility, salt extractability, and antibody accessibility, as well as in their energy requirement for the chase reaction.

A method for rapid determination of zotepine by gas chromatography-mass spectrometry

A rapid and sensitive method using solid-phase extraction and gas chromatography-mass spectrometry (GC-MS) has been developed for the determination of zotepine (ZTP), an atypical neuroleptic, in human plasma. The detection limit of ZTP was 1 microgram/L. Standard curves over the concentration range from 2.5 to 100 micrograms/L had a good linearity. Intraassay variability ranged from 2.2 to 3.3% and interassay variability from 3.5 to 6.6% at the concentration range of 5-75 micrograms/L. Our preliminary data of single-dose kinetics of ZTP by using this method suggested that the peak time and elimination half-life was much longer than previously reported, and that there appeared to be a second peak after 10-12 h of ZTP administration, indicating the possibility of the presence of enterohepatic recirculation.

Mutation in p53 and de-regulation of p53-related gene expression in three human cell lines immortalized with 4-nitroquinoline 1-oxide or 60Co gamma rays

In vitro models of malignant transformation of human cells may provide considerable insight into the mechanisms of multi-step carcinogenesis. It is well established that normal human cells must be immortalized before they can be malignantly transformed; however, they are stringently destined for aging and are rarely immortalized. The mechanism of cellular aging and immortalization is still unknown. We detected expression of only mutated p53 mRNA by direct sequencing of the reverse-transcribed mRNA in 3 human cell lines immortalized either with 4-nitroquinoline 1-oxide or with 60Co gamma rays. Consequently, only the mutated pS3 protein was expressed in each immortalized cell line. The expression of sdiI/p21 and mdm2, both of which are positively regulated by wild-type p53, was significantly down-regulated in the immortalized cell lines, resulting in over-expression of cdk2 and cdk4. Introduction of the sdiI/p21 gene into these cells was followed by a remarkable decrease in their ability to synthesize DNA. These results indicate that the p53 cascade may play an important role in the immortalization of human cells.

Interleukin-6 gene expression is preferentially restricted in VLA-5-MPC-1- immature but not in VLA-5+MPC-1+ mature myeloma cells

Interleukin-6 (IL-6) is essential for the proliferation of myeloma cells, and IL-6 is considered to be produced from not only myeloma cells themselves but also microenvironments including stromal cells. To clarify which subpopulation of myeloma cells can produce IL-6, we examined IL-6 mRNA expression in immature and mature myeloma cells and normal plasma cells by RT-PCR. IL-6 mRNA expression was found in all (10/10) specimens of sorted VLA-5-MPC-1- immature myeloma cells and 27% (3/11) of VLA-5-MPC-1+ myeloma cells. On the contrary, no IL-6 mRNA was expressed in VLA-5+MPC-1+ mature myeloma cells (0/4) and CD19+CD56- normal plasma cells (0/5). IL-6R gene expression was detected in all normal and malignant plasma cells without exception. Therefore, these findings suggest that IL-6 production is preferentially restricted in immature not mature myeloma cells, and this may explain why immature myeloma cells show greater proliferative activity.