[Two cases of therapy-related myelodysplastic syndrome]

Myelodysplastic syndrome (MDS) was sorted out two types; primary type and secondary type caused by irradiation or several drugs. Clinical features and chromosomal analysis were investigated in two patients with secondary MDS, caused by cyclophosphamide (CPM) or rifampicin (RFP) respectively, and fourteen cases of primary MDS hospitalized from 1988 to 1993. Two cases of secondary MDS progressed refractory anemia with excess of blasts (RAEB), however two of 14 patients with primary MDS progressed to acute leukemia. Median survival was similar in two groups. In cytogenitic analysis, complex abnormalities including -5/5q- and/or -7/7q- have two cases of secondary MDS and nine out of 14 cases of primary MDS. Complex chromosomal abnormalities did not improve following chemotherapy. In this study, clinical features and cytogenetic analysis demonstrated no significant difference between primary and secondary MDS.

Two cases of metastatic malignant melanoma of the lower limb treated with hyperthermic isolated limb perfusion and concomitant infusion of either carboplatin or beta-interferon

Two cases of metastatic malignant melanoma of the lower limb who were treated successfully with hyperthermic isolated limb perfusion are reported. One patient was infused with cisdiammine (1.1-cyclobutanedicarboxylate) platinum (II) (carboplatin, Paraplatin, Bristol-Myers Squibb Company, New Jersey, USA), and the other was infused with human natural beta-interferon (Feron, Toray, Tokyo, Japan), via the external iliac artery. The first case showed a remarkable suppression of the growth of multiple metastatic melanoma nodules associated with numerous melanophage infiltrations, as shown histopathologically after the operation. The patient's serum level of 5-S-cysteinyl dopa decreased for the two months following the treatment. In the second case, new formation of metastatic melanoma nodules was completely suppressed for up to 12 months following the operation. Analysis of immunological parameters showed that the number of peripheral CD8+ lymphocytes gradually and constantly increased after the operation, while that of CD4+ lymphocytes transiently increased and then returned to the pre-operative level. Natural killer activity transiently decreased to a slight degree 4 days after the operation and then returned to the pre-operative level 21 days after the operation. Side effects, such as nausea, vomiting and leg discomfort, were seen in the patient (Case 1) treated with carboplatin, but were completely reversible. These results suggest that hyperthermic isolated limb perfusion with concomitant infusion of carboplatin or beta-interferon is effective in suppressing the growth of metastatic malignant melanomas of the lower limb.

Open reduction of chronic lunate and perilunate dislocations

Four patients with chronic lunate and perilunate dislocations were treated by open reduction and internal fixation. The interval between injury and operation was 7, 8, 14 and 18 weeks, respectively. Both palmar and dorsal surgical approaches were needed to reduce the old dislocation in all cases. A case of dorsal trans-scaphoid perilunate dislocation showed concurrent partial disruption of the scapholunate ligament. Transient vascular compromise of either the lunate or the proximal scaphoid fragment was noted in three patients. Despite the delay in treatment, all patients had satisfactory outcomes.

Lithium side effects in relation to brain lithium concentration measured by lithium-7 magnetic resonance spectroscopy

1. The relationship between lithium (Li) side effects and brain Li concentration was examined in 17 patients with bipolar disorder treated with Li and other psychotropic drugs. 2. Brain Li concentration was measured by Li-7 magnetic resonance spectroscopy (MRS). Side effects were assessed using the UCLA General Side Effect Rating Scale For Lithium Treatment (GSE). 3. There was no correlation between the total GSE score and the brain, serum, or erythrocyte Li concentrations. Patients with hand tremor had significantly higher brain Li level (0.51 + or - 0.27 mM) than those without apparent tremor (0.36 + or - 0.20 mM), but no significant difference in serum Li level was seen. As far as the patients had hand tremor, they rarely had brain Li concentration less than the therapeutic range (1 of 15 measurement). On the other hand, they often had brain Li levels less than the therapeutic range when they did not have apparent tremor (13 of 52 measurements). 4. This preliminary study suggests that hand tremor is associated with the brain Li concentration.

Modulation of platelet-activating factor synthesis by recombinant interferon-alpha in human renal cell carcinoma

Platelet-activating factor (PAF), a potent phospholipid chemical mediator of inflammation, is involved in multiple cellular functions. Since PAF has a strong effect on platelet aggregation and on the enhancement of capillary permeability, it is possible that this factor plays an important role in tumor progression. In human renal cell carcinoma (RCC), it has recently been reported that immunotherapy with interferon (IFN) is effective for the prevention of tumor recurrence and progression. To evaluate the role of PAF and the effect of interferon-alpha (IFN-alpha) on PAF production in RCC, we measured PAF content and the activity of choline phosphotransferase (CPT), an enzyme involved in the de novo biosynthesis of PAF, in RCC specimens obtained from 30 patients who had undergone radical nephrectomy for RCC, and in specimens of normal renal cortex and normal renal medulla. PAF was present in both RCC and the normal renal tissues. Although CPT activity in RCC was similar to that in normal renal cortex, CPT activity in the normal medulla was significantly higher than that in RCC and the normal cortex. No correlation was found between CPT activity and the pathological findings in RCC. Although there was no difference in CPT activity in normal renal tissues between patients treated preoperatively with IFN-alpha and those untreated, CPT activity in RCC was significantly reduced in patients who had received IFN-alpha compared with those who had not. These findings suggest that IFN-alpha may modulate the production of PAF in RCC patients.

T helper cell subsets in the pathogenesis of systemic lupus erythematosus

It has been established that CD4+ T cells play an essential role in the development of systemic lupus erythematosus (SLE). Since CD4+ T cells differentiate upon activation into two defined subsets, TH1 and TH2, differing in their capacities of cytokine production with distinct immunopathological consequences, it becomes important to understand the respective roles of TH subsets in the pathogenesis of SLE. Our analysis on 4 different substrains of autoimmune-prone MRL mice revealed that the progression of SLE in these mice is correlated with an enhanced expression of interferon-gamma (a TH1 type cytokine regulating the production of IgG2a and IgG3) vs interleukin-4 (IL-4; a TH2 type cytokine regulating the production of IgG1), in parallel with an increased production of IgG2a and IgG3 autoantibodies over IgG1. In addition, studies on lupus-prone mice expressing an IL-4 transgene have shown that the constitutive expression of IL-4, biasing autoimmune responses towards a TH2 phenotype, inhibits the development of lupus nephritis. These results suggest that the development and progression of murine lupus is determined by the type of TH responses (either acceleration by TH1 responses or protection by TH2 responses) inducing the generation of more or less pathogenic autoantibodies. In fact, murine IgG3 has been shown to be extremely nephritogenic, generating "wire-loop" lupus-like glomerular lesions, because of their cryoglobulin activity associated with a unique physicochemical property of IgG3 constant region. Our results underline the importance in the pathogenesis of SLE of the qualitative aspects of autoantibody responses controlled by subpopulations of TH cells.

Hepatocellular carcinoma: detection with double-phase helical CT during arterial portography

Retrospective analysis of findings at double-phase helical computed tomography (CT) during arterial portography was performed in 42 hepatocellular carcinomas (HCCs) in 31 patients. Phase 1 scanning started 30-35 seconds after the beginning of injection of contrast material; phase 2 scanning started 10-18 seconds after the end of phase 1. The overall detection rate for HCCs was 83% (35 of 42) in phase 1, 81% (34 of 42) in phase 2, and 90% (38 of 42) for combined phase 1 and 2 findings.

Screening of plant growth regulators acting on Arabidopsis thaliana

Our screening system using Arabidopsis thaliana, enabled us to evaluate the effect of 38 known growth regulators on plant growth promotion. Eleven compounds in the study were found to show a promoting effect upon Arabidopsis dry weight and leaf number; in particular, oligosaccharides (OS) such as raffinose and stachyose had a marked effect. Detailed experiments indicated that the effect of OS on plant growth was not merely derived from its potential carbon source. Among the monosaccharides comprising stachyose, galactose showed the best promoting effect on plant growth.

Immunohistochemical localization of aldehyde and xanthine oxidase in rat tissues using polyclonal antibodies

Tissues from male Wistar rats, fixed with 4% paraformaldehyde and embedded in paraffin, were studied with immunoperoxidase techniques using polyclonal antibodies raised against aldehyde oxidase or xanthine oxidase purified from rat liver. Immunohistochemical studies demonstrated that aldehyde oxidase-bearing cells were strongly stained in renal tubules, esophageal, gastric, intestinal and bronchial epithelium as well as liver cytoplasm. Weak but positive immunoreactivity was observed on the pulmonary alveolar epithelial cells, gastric glands and intestinal goblet cells. In contrast, it was demonstrated that cells with xanthine oxidase were strongly stained in renal tubules, esophageal, gastric, and small and large intestinal and bronchial epithelia etc. Positive immunostaining was also found in adrenal gland, skeletal muscle, spleen and cerebral hippocampus. Immunoreactivity againt aldehyde oxidase was not found in adrenal gland, spleen, mesentery or aorta, while immunoreactivity against xanthine oxidase was not found in mesentery or aorta. Although the significance of this ubiquitous and similar localization of aldehyde and xanthine oxidase seems unclear at present, these results may provide a clue as to the full understanding of the pathophysiological role of these oxidases in tissues.

Observation of macular lesion in Best's vitelliform macular dystrophy by scanning laser ophthalmoscope

Using a scanning laser ophthalmoscope (SLO), the ocular fundus of a patient with Best's vitelliform macular dystrophy was examined. With the argon blue laser, a dark area was seen in the fovea. Areas of weakly bright reflex were seen corresponding to the scrambled-egg lesion observed by ophthalmoscope. With the argon green laser, highly bright spots were observed at the foveola. Intense bright reflex was seen over the scrambled-egg lesion at the posterior pole. The helium-neon laser revealed highly bright patches corresponding to the orderly ring distribution of the yellowish deposits at the posterior pole. The diode laser revealed a mottled appearance with dark and bright patches in the scrambled-egg lesion. SLO provided a morphologic enhancement in the specifically affected layers of the macula in Best's vitelliform macular dystrophy.

Effect of amino acids on the excretions of purine bases and oxypurinol

To investigate whether or not amino acids affect the urinary excretion of purine bases and oxypurinol, a 12% amino acid solution was infused to 6 subjects who took allopurinol (300 mg) 6 h before the study. Amino acid infusion increased the urinary excretion and the fractional clearance of uric acid and oxypurinol and decreased the plasma concentration of oxypurinol. However, it affected neither the urinary excretion, the fractional clearance, the plasma concentration of oxypurines nor the plasma concentration of uric acid. These results indicate that amino acids affect the renal transport pathways of oxypurinol and uric acid but not those of oxypurines. In addition, it was suggested that the amino acid-induced increase in the urinary excretion of oxypurinol may be considered when allopurinol is administered to hyperuricemic patients with hypoproteinemia who have taken amino acids either orally or intravenously.

Nitric oxide and endothelin 1 during postnatal life

Nitric oxide (NO) is a potent vasodilator produced by endothelial cells. Endothelin 1 (ET-1), another agent made by endothelial cells, is the most potent vasoconstrictor known to date. Endogenous NO and ET-1 may play a part in the normal physiological pulmonary vascular changes during the postnatal period. However, the changes of NO and ET-1 in healthy neonates have not been defined. We determined serum NO metabolites, i.e., nitrites and nitrates, and plasma ET-1 in 19 healthy neonates at birth (cord blood) and at ages 5 and 30 days. The sums of serum nitrite and nitrate (NOx) levels were 27.5 +/- 12.8, 53.8 +/- 14.2, and 38.3 +/- 13.2 mumol/l at birth, age 5 days, and age 30 days, respectively. The plasma ET-1 concentrations were 3.9 +/- 1.6, 1.1 +/- 0.2, and 1.1 +/- 0.2 x 10(6) mumol/l at birth, age 5 days, and age 30 days, respectively. These changes in healthy neonates suggest the presence of active physiological roles for NO and ET-1 in circulatory adaptation to extra-uterine life.

[Studies on solid phase extraction of bile acids from biological matrix]

To quantify bile acids in biological samples, a solid phase extraction method was examined. This method is known as simpler procedures with less contamination compared with solvent extraction methods. Rat bile, feces and urine were used as biological samples. Since Bond Elut C18 and C8 were proved to be more suitable than the other phases (CH and SAX) so far examined using standard bile acids, Bond Elut C18 was used for biological samples. Quantification of biological sample was carried out by gas chromatography after the extracted sample was derivatized to methyl ester by treatment with trimethylsilyldiazomethane then to trifluoroacetyl ester by trifluoroacetic anhydride. On the gas chromatography, two columns (Rtx-50 and Rtx-200) were connected to the injector with Y-tube for elimination of interference. Except for a few bile acids, high recovery with less biological contamination was obtained by this solid phase extraction method.

Stimulatory effect of leminoprazole on secretion and synthesis of mucus by rabbit gastric mucosal cells

We examined whether leminoprazole (an acid pump inhibitor) enhances the secretion and synthesis of gastric mucus in vitro. Mucosal cells were prepared from male rabbit stomachs, and the amounts of secreted and synthesized mucus were determined by the [3H] glucosamine labeling method. Exposure of gastric mucosal cells to leminoprazole at 1 to 100 microM for 8 hr caused significant increases in the secretion and synthesis of mucus in a dose-related manner, but omeprazole was not effective. The stimulatory effects of leminoprazole on secretion and synthesis were observed 4 hr and 6 hr later, respectively. In contrast, both 16,16-dimethyl prostaglandin E2 and nitroprusside, a nitric oxide (NO) generator, caused marked increases in mucus secretion and synthesis even after 2-hr incubation. The effects of leminoprazole on gastric mucus were strongly inhibited by NO synthase inhibitors such as NG-nitro-L-arginine methyl ester and NG-monomethyl-L-arginine and by the NO scavenger oxyhemoglobin. However, neither indomethacin (an inhibitor of cyclooxygenase), aminoguanidine (an inhibitor of inducible nitric oxide synthase) nor cycloheximide (a protein synthesis inhibitor) could suppress its effects. These results suggest that leminoprazole stimulates the secretion and synthesis of gastric mucus after a lag period, probably through NO produced by constitutive NO synthase.

Inhibition of tumor necrosis factor in the brain suppresses rabbit sleep

Tumor necrosis factor (TNF) is a cytokine that possesses many biological activities, including enhancement of non-rapid-eye-movement sleep (NREMS). The role of endogenous TNF in the regulation of spontaneous sleep is unknown. If TNF is involved in sleep regulation, then reduction of endogenous TNF should suppress spontaneous sleep. A soluble TNF-binding protein I (TNF-BP I) and a synthetic fragment of TNF-BP I, TNF-R-(159-178), that contains the biologically active region of TNF-BP I, were used. These substances bind TNF and possess TNF-inhibitory activity; their effects on rabbit sleep after intracerebroventricular injection were determined across a 6-h recording period. Two doses of TNF-BP I (0.05 micrograms and 0.5 micrograms) were administered; the higher dose of TNF-BP I significantly decreased NREMS. Four doses of TNF-R-(159-178) (0.25 micrograms, 2.5 micrograms, 25 micrograms and 50 micrograms) were used. The 25 micrograms and 50 micrograms doses significantly suppressed NREMS. The highest dose (50 micrograms) also decreased REM sleep. These results are consistent with the hypothesis that endogenous brain TNF is involved in the regulation of normal sleep.

Role of C5a-ase in group B streptococcal resistance to opsonophagocytic killing

Type III group B streptococci (GBS) can be subdivided into three subtypes, RDP III-1, III-2, and III-3, on the basis of numerical analysis of HindIII restriction endonuclease digestion patterns (HindIII RDP) with their chromosomal DNAs. In the present study, the effect of C5a on opsonophagocytic killing of a representative strain from each RDP type was investigated by using a novel optical method for determining opsonophagocytic killing, and the effect of C5a-ase treatment of C5a on opsonophagocytic killing was also investigated. Pre-stimulation of polymorphonuclear leukocytes (PMNs) with C5a significantly increased opsonophagocytic killing of all three strains. The increase in killing was abolished by pretreating the C5a with GBS that express C5a-ase, a treatment that also destroyed the chemoattractant activity of the C5a. The kinetics of killing of the RDP III-2 strain differed from those of the other two strains. The survival of the RDP III-2 bacteria continued to decline over the entire 60-min incubation of the opsonophagocytic assay when PMNs were prestimulated with C5a or with C5a that had been inactivated with GBS C5a-ase (dC5a). In contrast, killing of the RDP III-1 and III-3 strains almost ceased after 20 or 60 min when PMNs were prestimulated with dC5a or C5a, respectively. A difference in bacterial killing between the III-2 strain and the III-1 and III-3 strains therefore became increasingly apparent with prolonged incubation time. The percentage of bacteria surviving in the extracellular fluid was approximately the same as the percentages of bacteria surviving in both intracellular and extracellular locations when PMNs were prestimulated with either C5a or dC5a. These data imply that the majority of bacterial killing occurred following phagocytosis and suggest that the enhanced killing of GBS following prestimulation of PMNs with C5a resulted from increased ingestion of the bacteria.

A histamine H2 receptor antagonist, roxatidine, stimulates mucus secretion and synthesis by cultured rabbit gastric mucosal cells

We examined the effects of the known antisecretory and mucosal protective drug, roxatidine, on the secretion and synthesis of mucus by cultured rabbit gastric mucosal cells. The amounts of secreted and synthesized mucus were determined by the [3H] glucosamine labelling method. Exposure of the cells to roxatidine for 8 hr caused increases in the secretion and synthesis of mucus in a dose-related manner. The increase in mucus synthesis was maximally induced 4 hr after the addition of roxatidine, while mucus secretion was maximally enhanced a further 4 hr later. However, other H2 antagonists such as cimetidine, rantidine and famotidine failed to stimulate the secretion and synthesis of gastric mucus. In addition, neither indomethacin nor NG-nitro-L-arginine methyl ester affected the roxatidine-induced increases in mucus secretion and synthesis. We conclude that roxatidine directly acts on gastric mucosal cells, inducing increases in both the secretion and synthesis of mucus, and that an unknown regulatory pathway might be involved in these stimulatory actions of roxatidine.

Protein kinase C activation in the heart: effects on calcium and contractile proteins

BACKGROUND

Cardiac contractile function is dependent on the energetic state of the heart, intracellular calcium levels, and the interaction of the contractile proteins with both adenosine triphosphate and calcium. Protein kinase C (PKC) is a ubiquitous intracellular mediator that has been found in the heart and has been shown to phosphorylate proteins that regulate calcium homeostasis (calcium channels) and the contractile proteins themselves (troponin I and troponin T).

METHODS

To determine the role of PKC activation on cardiac contractile function, direct activation of PKC was achieved by the infusion of phorbol 12-myristate 13-acetate, an activating phorbol ester. The effects of PKC activation were evaluated in Langendorff-perfused rabbit hearts. Contractile function, high-energy phosphate content (phosphorous-31 nuclear magnetic resonance spectroscopy), oxygen consumption, and intracellular calcium levels (calcium fluorescent dye Rhod-2) were determined.

RESULTS

Activation of PKC in the heart by phorbol 12-myristate 13-acetate resulted in a significant decrease in both systolic and diastolic function while oxygen consumption and adenosine triphosphate production remained unchanged. Both baseline and peak intracellular calcium levels decreased, which may contribute to the impaired systolic function.

CONCLUSIONS

Activation of PKC in the heart leads to significant loss of contractile function without affecting energetics. The effect is most likely due to alteration in cytosolic calcium regulation and altered contractile sensitivity to calcium.

Multiple neuroepithelial tumors of different cell types--case report

A 31-year-old male developed intramedullary tumors in the medulla oblongata and the upper cervical spinal cord. He was first admitted with tetraparesis. Magnetic resonance (MR) imaging revealed a low intensity mass lesion in the medulla oblongata. The tumor was removed and diagnosed as a pilocytic astrocytoma. Nine years later, he was readmitted with motor weakness and dysesthesia in the right arm. MR imaging revealed a mass lesion in the cervical cord. This tumor was removed and diagnosed histologically as ependymoma. We suggest that the displacement of primitive spongioblasts with subsequent differentiation resulted in an astrocytoma and an ependymoma in adjacent areas.

Reaction of cytochrome bo3 with oxygen: extra redox center(s) are present in the protein

The reaction of oxygen with cytochrome bo3, a quinol oxidase from Escherichia coli, has been studied by resonance Raman scattering after initiation of the reaction by CO photolysis in a continuous flow apparatus and by directly mixing the enzyme with oxygen. The high-frequency region of the spectrum was monitored to determine the time evolution of the spin, oxidation, and coordination states of heme O and the oxidation state of heme B by using newly established marker lines for each heme. Three phases of the reaction were detected. In phase I, complete in 75 microseconds, O2 reacted with heme O and formed a low-spin ferric or ferryl adduct without significant oxidation of heme B. In phase II, between 75 and 120 microseconds, a small fraction of heme B was oxidized. In phase III, at approximately 1 s, the majority of heme B was oxidized and heme O reverted to a high-spin ferric state. The high rate of oxygen reduction at heme O to the three- or four-electron reduced level, despite a very low rate of heme B oxidation, indicates that there are electron donors active in the enzyme other than the metal centers. Assays of our enzyme preparations rule out a quinol in the tight binding (QH) site as a possible donor but instead suggest electron donation from the protein matrix, such as from tryptophans or tyrosine.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of furin to the trans-Golgi network and recycling from the cell surface involves Ser and Tyr residues within the cytoplasmic domain

Furin is a membrane-associated endoprotease that catalyzes cleavage of precursor proteins at Arg-X-Lys/Arg-Arg sites. Although, at steady state, furin is predominantly found in the trans-Golgi network (TGN), it also cycles between the TGN and the cell surface. Recently, the cytoplasmic tail of furin has been shown to be sufficient for its localization to the TGN. Within the cytoplasmic domain, there are Ser residues, which we now show are sites for phosphorylation by casein kinase II in vitro, and a Tyr-containing sequence, both of which have been shown to be important for other TGN proteins to localize to this compartment. In the present study, we show by site-directed mutagenesis that these residues are important for TGN localization and recycling of furin. Mutation of the Ser residues abrogated the TGN localization. By contrast, mutation of the Tyr residue did not affect the TGN localization but impaired the internalization from the plasma membrane. These observations suggest that distinct cytoplasmic determinants are responsible for retention in the TGN and retrieval from the cell surface of furin.

Chromosomal anomalies in prostatic intraepithelial neoplasia and carcinoma detected by fluorescence in situ hybridization

The pathogenetic relationship between high-grade prostatic intraepithelial neoplasia (PIN), prostatic carcinoma, and metastases is poorly understood. We used fluorescence in situ hybridization (FISH) with centromere-specific probes for chromosomes 7, 8, 10, 12, and Y to evaluate numeric chromosomal anomalies in PIN (68 foci), localized prostatic carcinoma (78 foci), and lymph node metastases (8 foci) in 40 whole-mount radical prostatectomy and pelvic lymphadenectomy specimens. Chromosomal anomalies were found in 50, 51, and 100% of the foci of PIN, carcinoma, and metastases, respectively. The mean numbers of abnormal chromosomes per focus were 0.66 in PIN, 1.09 in carcinoma, and 3.75 in metastases. The most frequent anomaly in PIN was a gain of chromosome 8 (32% of foci), followed by gains of chromosomes 10 (13%), 7 (10%), 12 (4%), and Y (4%). The most frequent anomalies in foci of carcinoma were gains of chromosomes 7 and 8 (28% and 30% of foci, respectively), followed by gains of chromosomes 10 (23%), 12 (9%), and Y (9%). There was a positive correlation of the gain of chromosome 8 with the pathological stage and Gleason score (both P < 0.05). Usually, carcinoma foci contained more anomalies than paired PIN foci, but five prostates contained one or more foci of PIN with more anomalies than carcinoma. Among the cases with metastases, usually one or more foci of the primary tumor shared chromosomal anomalies with the matched metastases. Our results indicate that PIN and prostatic carcinoma foci have similar proportions of chromosomal anomalies, but foci of carcinoma usually have more alterations. This observation supports the hypothesis that PIN is often a precursor of carcinoma, although there are some carcinoma foci that have few or no apparent chromosomal alterations, whereas concurrent PIN foci have multiple alterations. A gain of chromosome 8 was the most common numerical alteration and was associated with increasing cancer stage and grade, suggesting that it may play a role in the initiation and progression of prostatic carcinoma. Usually, one or more foci of the primary tumor shared chromosomal anomalies with associated lymph node metastases, suggesting that, often, just a single focus of carcinoma gives rise to metastases.

A second mutant allele of furin in the processing-incompetent cell line, LoVo. Evidence for involvement of the homo B domain in autocatalytic activation

Furin is a Golgi membrane-associated endoprotease that is involved in cleavage of various precursor proteins predominantly at Arg-X-Lys/Arg-Arg sites. Furin itself is synthesized as an inactive precursor, which is activated through intramolecular autocatalytic cleavage at an Arg-X-Lys-Arg site. We previously found that human colon carcinoma LoVo cells have a frameshift mutation within the homo B domain of furin and thereby lack processing activity toward Arg-X-Lys/Arg-Arg sites. In this study, however, we identified a second furin mutation in this cell line. The mutation, a replacement of a conserved Trp residue within the homo B domain with Arg, results in lack of processing activity of the mutant furin. The combination of both mutations can account for the recessive nature of the processing incompetence of LoVo cells. Immunofluorescence analysis with three distinct anti-furin monoclonal antibodies revealed that neither furin mutant underwent the autocatalytic activation or left the endoplasmic reticulum for the Golgi. These data indicate that the homo B domain as well as the catalytic domain is required for autocatalytic activation of furin.