tau kinases in the rat heat shock model: possible implications for Alzheimer disease.

We have previously shown, by using the phosphate-dependent anti-tau antibodies Tau-1 and PHF-1, that heat shock induces rapid dephosphorylation of tau followed by hyperphosphorylation in female rats. In this study, we analyzed in forebrain homogenates from female Sprague-Dawley rats the activities of extracellular signal regulated kinase 1/2 (ERK1/2), c-Jun NH(2)-terminal kinase (JNK), glycogen synthase kinase-3beta (GSK-3beta), cyclin-dependent kinase 5 (Cdk5), cAMP-dependent protein kinase A (PKA), and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) at 0 (n = 5), 3 (n = 4), 6 (n = 5), and 12 (n = 5) h after heat shock and in non-heat-shocked controls (n = 5). Immunoprecipitation kinase assays at 0 h showed suppression of the activities of all kinases except of GSK-3beta, which showed increased activity. At 3-6 h, the activities of ERK1/2, JNK, Cdk5, and GSK-3beta toward selective substrates were increased; however, only JNK, Cdk5, and GSK-3beta but not ERK1/2 were overactivated toward purified bovine tau. At 3-6 h, kinase assays specific for PKA and CaMKII showed no increased activity toward either tau or selective substrates. All of eight anti-tau antibodies tested showed dephosphorylation at 0 h and hyperphosphorylation at 3-6 h, except for 12E8, which showed hyperphosphorylation also at 0 h. Immunoblot analysis using activity-dependent antibodies against ERK1/2, JNK, and GSK-3beta confirmed the above data. Increased activation and inhibition of kinases after heat shock were statistically significant in comparison with controls. Because tau is hyperphosphorylated in Alzheimer disease these findings suggest that JNK, GSK-3beta, and Cdk5 may play a role in its pathogenesis.

Hypothalamic Langerhans cell histiocytosis with no eosinophils.

A 26-year-old man presented with diabetes insipidus, sexual dysfunction and memory impairment. Nuclear magnetic resonance imaging and pathologic examination revealed Langerhans cell histiocytosis of the hypothalamus, which contained no eosinophils. The lesional cells were positive for S-100 protein and CD1a antigen, and negative for CD68 antigen. The possible pathogenesis, absence of eosinophils and prognosis are discussed.

Androgens Prevent the Heat Shock-Induced Hyperphosphorylation but not Dephosphorylation of t in Female Rats. Implications for Alzheimer's Disease.

We have previously shown that heat shock induces rapid dephosphorylation of tau in both female and male rats followed by hyperphosphorylation only in female rats (J Neurochem 66 (1996), 1140-1149). We have also shown that the heat shock-induced hyperphos-phorylation of tau is estrogen-independent in female rats and prevented by androgens in male rats (Proc Natl Acad Sci USA 94 (1997), 6612-6617). To investigate whether androgens could prevent the hyperphosphorylation of tau also in female rats, twenty-three 2- to 3-month-old Sprague-Dawley rats were ovariectomized and given daily subcutaneous injections of 1 mg/250 g of testosterone propionate for 3-5 weeks. Immunoblots of SDS cerebral extracts were analysed qualitatively using the peroxidase-antiperoxidase technique and phosphate-dependent and -independent anti-tau antibodies, and quantitatively using Tau-1 and 125I-labeled protein A. We have found that while at 0 h after heat shock tau was dephosphorylated, at 3 h and 6 h after heat shock tau was not hyperphosphorylated, as would be the case in non-androgen-treated female rats (ref. above). In addition, tau became dephosphorylated in non-heat-shocked control rats. Because tau is abnormally hyperphosphorylated in Alzheimer's disease, the possibility of using combined estrogen/androgen replacement therapy in postmenopausal women as a preventive measure against Alzheimer's disease should be investigated.

The heat shock-induced hyperphosphorylation of tau is estrogen-independent and prevented by androgens: implications for Alzheimer disease.

We have shown that heat shock induces rapid dephosphorylation of tau in both female and male rats followed by hyperphosphorylation only in female rats. To investigate the role of gonadal hormones, rats were ovariectomized (OVX), orchiectomized (ORX), or sham-gonadectomized and received replacement therapy with estradiol benzoate (EB), testosterone propionate (TP), or sesame oil (SO) vehicle for 2-3 weeks, respectively. At 0, 3, 6, and 12 hr after heat shock, immunoblot analysis of SDS cerebral extracts was performed using phosphate-dependent and -independent anti-tau antibodies. Seven groups of rats were analyzed: (i) sham-OVX + SO; (ii) OVX + SO; (iii) OVX + EB; (iv) sham-ORX + SO; (v) ORX + SO; (vi) ORX + TP; and (vii) ORX. In all seven groups, there was dephosphorylation of tau at 0 hr after heat shock. In all three groups of female rats, there was hyperphosphorylation of tau at 3 hr after heat shock, and its degree and temporal pattern were identical between the OVX + SO and OVX + EB groups. In male rats, there was hyperphosphorylation of tau at 3 hr after heat shock in both ORX + SO and ORX groups, and its degree was reduced in the ORX + TP group. Thus, dephosphorylation of tau is gonadal hormone-independent, but while its hyperphosphorylation is estrogen-independent it is prevented by androgens. Because tau is abnormally hyperphosphorylated in Alzheimer disease, which is more frequent in women than men, these findings suggest that androgens may exert a neuroprotective effect.

Heat shock induces rapid dephosphorylation of tau in both female and male rats followed by hyperphosphorylation only in female rats: implications for Alzheimer's disease.

Female and male 2-3-month-old Sprague-Dawley rats were heat shocked at 42 degrees C for 15 min. At 0, 3, 6, 12 and 24 h after heat shock, qualitative and quantitative immunoblot analysis of cerebral extracts and immunohistochemistry were performed using monoclonal anti-tau antibodies that recognize nonphosphorylated (Tau-1), phosphorylated (PHF-1), and phosphate-independent (Tau-5 and Tau-46) epitopes. At 0 h after heat shock, there was dephosphorylation of tau in both female and male rats as evidenced by (1) accentuation and attenuation of tau isoforms recognized by Tau-1 and PHF-1, respectively, and recognition of additional tau polypeptides by Tau-1, Tau-5, and Tau-46 but not PHF-1; (2) significant increase in the nonphosphorylated Tau-1 epitope with resultant decrease in the ratio of total (phosphorylated plus nonphosphorylated) tau to nonphosphorylated tau; and (3) dephosphorylation of the Tau-1 epitope in the somatodendritic compartment. By 6 h after heat shock, there was progressive hyperphosphorylation of tau in female but not male rats exemplified by (1) upward gel mobility shift recognized by PHF-1, Tau-5, and Tau-46, and by Tau-1 after dephosphorylation; (2) significant increase in the ratio of total tau to nonphosphorylated tau; and (3) rephosphorylation of the Tau-1 epitope in the somatodendritic compartment. Two-dimensional electrophoresis showed shifts to basic and acidic tau polypeptides at 0 and 6 h after heat shock, respectively. Hyperphosphorylation of tau also occurred after multiple heat-shock episodes. Microtubules were present at 6 h after heat shock. There were no differences between control and heat-shocked rats in extracts from peripheral nerves. Thus, we now have a simple rat model to study within 6 h the processes of dephosphorylation and hyperphosphorylation of tau, which are altered in Alzheimer's disease.

Leptomeningeal fibroma.

Few cases of benign fibrous tumors have been reported in the central nervous system. Of the 9 cases in the literature only 1 was adjacent to the leptomeninges. We report a case of a fibroma of the leptomeninges of very low cellularity with calcified areas that had typical findings of a fibroma by electron microscopy. Immunophenotyping revealed unexpected positivity for S-100 and glial fibrillary acidic proteins. The histogenesis of this lesion may be a pluripotential cell, or the expression of these antigens may be induced by local factors in the central nervous system. The incidence of this unusual lesion is unknown, and ours is more typical of extracranial fibromas than the previously reported cases.

Functional implications for the microtubule-associated protein tau: localization in oligodendrocytes.

We present evidence that the microtubule-associated protein tau is present in oligodendrocytes (OLGs), the central nervous system cells that make myelin. By showing that tau is distributed in a pattern similar to that of myelin basic protein, our results suggest a possible involvement of tau in some aspect of myelination. Tau protein has been identified in OLGs in situ and in vitro. In interfascicular OLGs, tau localization, revealed by monoclonal antibody Tau-5, was confined to the cell somata. However, in cultured ovine OLGs with an exuberant network of processes, tau was detected in cell somata, cellular processes, and membrane expansions at the tips of these processes. Moreover, in such cultures, tau appeared localized adjacent to or coincident with myelin basic protein in membrane expansions along and at the ends of the cellular processes. The presence of tau mRNA was documented using fluorescence in situ hybridization. The distribution of the tau mRNA was similar to that of the tau protein. Western blot analysis of cultured OLGs showed the presence of many tau isoforms. Together, these results demonstrate that tau is a genuine oligodendrocyte protein and pave the way for determining its functional role in these cells.

Rapid dephosphorylation of tau in heat-shocked fetal rat cerebral explants: prevention and hyperphosphorylation by inhibitors of protein phosphatases PP1 and PP2A.

We heat shocked 21- and 35-day-old fetal rat cerebral explants at 45 degrees C for 18 min and performed immunocytochemistry and immunoblot analysis of sodium dodecyl sulfate extracts using the monoclonal anti-tau antibodies Tau-1, Tau-5, Tau-46, and PHF-1 and the peroxidase-antiperoxidase technique or 125I-labeled protein A. Tau-1 and PHF-1 recognize nonphosphorylated and phosphorylated epitopes, respectively, and both Tau-5 and Tau-46 recognize phosphate-independent epitopes. tau immunoreactivity was confined to neurons and increased in heat-shocked perikarya but not axons. At 0 h after heat shocking, there was dephosphorylation of tau exemplified by (1) faster migration of tau isoforms with resultant loss or attenuation of the 60- and 52-kDa tau isoforms recognized by all four anti-tau antibodies and concomitant accentuation of the fastest moving 50-kDa tau isoform recognized by Tau-1, Tau-5, and Tau-46; and (2) significant increase in the nonphosphorylated Tau-1 epitope with resultant decreases in the ratio of total (phosphorylated plus nonphosphorylated) tau to nonphosphorylated tau and the difference of total tau minus nonphosphorylated tau. tau was phosphorylated back to the control level by 12 h and remained so at 24 and 48 h after heat shocking. Treatment of explants with cycloheximide, a protein synthesis inhibitor, did not prevent the heat shocking-induced dephosphorylation of tau. Treatment of explants with the inhibitors of protein phosphatases PP1 and PP2A, okadaic acid or calyculin A, produced hyperphosphorylated tau polypeptides, prevented the heat shocking-induced dephosphorylation of tau, and intensified the immunoreactivity of the neurofilament subunit H with the only antiphosphoneurofilament antibody that reacts with intraneuronal neurofibrillary tangles. In 35-day-old explants, in addition to the three 50-, 52-, and 60-kDa tau isoforms seen in 21-day-old explants, a 66-kDa tau polypeptide was also present.

Nuclear tau immunoreactivity in presenile dementia with motor neuron disease: a case report.

We report for the first time localization of tau immunoreactivity with neuronal nuclei in an autopsy case of a 64-year-old white male with a 10-year history of presenile dementia with motor neuron disease. The anti-tau mAbs Tau-1, Tau-2, Tau-5 and PHF-1 and the anti-phosphoneurofilament mAb SMI-31, which crossreacts with tau, stained neuronal nuclei in neocortical pyramidal layer V or in layer III of primary motor cortex, in the periamygdaloid and entorhinal cortices, in pons and in a few paramedian neurons in dorsal medulla. The staining was excluded from nucleoli.

Proton magnetic resonance imaging and spectroscopic studies of the pathogenesis and treatment of juvenile dermatomyositis.

Juvenile dermatomyositis is an inflammatory disorder of muscle, skin, and connective tissue. Immune vasculopathy is central to the pathophysiology. We studied a 13-year-old boy with juvenile dermatomyositis using proton magnetic resonance imaging (MRI) with short tau inversion recovery (STIR), and proton magnetic resonance spectroscopy (MRS) to quantitate lipid and water in affected regions of muscle. Tissue perfusion was assessed by measuring tissue water concentration changes during isometric exercise of the tibialis anterior muscle. During sequential studies over 3 months of steroid treatment, STIR image abnormalities, resting water concentrations, and diminished perfusion returned to normal. Resting lipid concentrations increased during this period. MRI serves to guide muscle biopsy and monitor progress of the disease state. MRS demonstrates the vasculopathy and provides noninvasive assessment of steroid therapy in juvenile dermatomyositis.

Altered phosphorylation of tau protein in heat-shocked rats and patients with Alzheimer disease.

Six hours after heat shocking 2- to 3-month-old male and female Sprague-Dawley rats at 42 degrees C for 15 min, we analyzed tau protein immunoreactivity in SDS extracts of cerebrums and peripheral nerves by using immunoblot analysis and immunohistochemistry with the anti-tau monoclonal antibody Tau-1, which recognizes a phosphate-dependent non-phosphorylated epitope, and with 125I-labeled protein A. In the cerebral extracts, we found altered phosphorylation of tau in heat-shocked females, characterized by a marked reduction in the amount of nonphosphorylated tau, a doubling of the ratio of total (phosphorylated plus nonphosphorylated) tau to nonphosphorylated tau, and the appearance of the slowest moving phosphorylated tau polypeptide (68 kDa). Similar, but milder, changes were observed in male rats. These changes progressively increased in females from 3 to 6 h after heat shocking. In contrast, both phosphorylated tau and nonphosphorylated tau were reduced in peripheral nerves after heat shocking. In immunoblots of SDS extracts from Alzheimer disease-affected brain, the two slowest moving phosphorylated tau polypeptides (62 kDa and 66 kDa, respectively) were detected by Tau-1 after dephosphorylation and by Tau-2 (an anti-tau-monoclonal antibody that recognizes a phosphate-independent epitope) without prior dephosphorylation only in regions that contained tau immunoreactivity in histologic preparations. In addition, quantitative immunoblot analysis of cortex and the underlying white matter with Tau-1 and 125I-labeled protein A showed that the amount of phosphorylated tau progressively increased in the Alzheimer disease-affected cerebral cortex, while concurrently a proportionally lesser amount of tau entered the white matter axons. The similar findings for the rat heat-shock model and Alzheimer disease suggest that life stressors may play a role in the etiopathogenesis of Alzheimer disease.

Phase I/II clinical trial of didemnin B in non-small-cell lung cancer: neuromuscular toxicity is dose-limiting.

Didemnin B (NSC 325,319), a cyclic depsipeptide isolated from a Caribbean tunicate, exhibits potent preclinical antitumor activity. In previous phase I studies, 3.47 mg/m2 was the maximally tolerated dose, with nausea and vomiting being the dose-limiting toxicity. The drug was given in a single bolus infusion over 30 min every 28 days. In the current study, 30 patients presenting with previously treated non-small-cell lung cancer (NSCLC) received 46 courses of the drug at doses ranging from 3.47 to 9.1 mg/m2. Neuromuscular toxicity was dose-limiting. Nausea and vomiting appeared to be correlated with dose levels and were ameliorated by a combination of antiemetics including dexamethasone. Other side effects included a mild rise in hepatic enzymes and an allergic reaction that was preventable by the addition of corticosteroids to the premedication regimen. In all, 2 minor responses were seen among 24 evaluable patients. Because neuromuscular toxicity is dose-limiting, we recommend that routine measurements of creatine kinase and aldolase, a careful neurologic evaluation, and electromyography and muscle biopsy (if indicated) be incorporated into phase II trials. The recommended dose for phase II studies using a single bolus schedule is 6.3 mg/m2, following the premedication of patients with antiemetics.

Primary intracerebral Hodgkin's disease: a case report.

The authors report a case of primary intracerebral Hodgkin's disease in an 84-year-old woman who presented with a solitary intraparenchymal parieto-occipital lesion and absence of extracranial disease. The histologic diagnosis of Hodgkin's disease was further confirmed with positive immunohistochemical staining of Hodgkin's mononuclear cells and Reed-Sternberg cells and electron microscopy. Such an initial presentation of a solitary intracerebral tumor is extremely rare in Hodgkin's disease. This case helps establish primary intracerebral Hodgkin's disease as a true entity.

Tau protein immunoreactivity in dementia of the Alzheimer type: II. Electron microscopy and pathogenetic implications. Effects of fixation on the morphology of the Alzheimer's abnormal filaments.

I have used Tau-1 and Tau-2, two monoclonal antibodies against tau protein, to study at the electron microscopic level the tau immunoreactivity in 8 cases with dementia of the Alzheimer type, using the peroxidase-antiperoxidase technique and formalin-fixed autopsy and biopsy brain tissues. In neurons and astrocytes, excessive amounts of tau immunoreactivity were noted in association with ribosomes. The Alzheimer's abnormal filaments in neurofibrillary tangles in neuronal perikarya, in senile plaques, and in a multitude of abnormal neuropil neurites were frequently stained intensely. However, many neurons contained either stained ribosomes only or stained ribosomes and unstained abnormal filaments both scattered and in neurofibrillary tangles. In all locations, the immunostained abnormal filaments were straight without appreciable periodic constrictions and, on cross-section, had a tubular appearance with stained walls, frequently demonstrable unstained lumens and an accentuation of staining intensity at the periphery. In addition, conventional electron microscopy showed that formalin-fixed and glutaraldehyde-fixed neurofibrillary tangles were made of compactly arranged straight filaments and loosely arranged paired helical filaments, whereas osmium tetroxide-fixed neurofibrillary tangles were made almost exclusively of paired helical filaments. These findings suggest that: (a) localization of excessive tau immunoreactivity with ribosomes might be the primary event and association of detectable tau immunoreactivity with already assembled filaments might be an epiphenomenon; and (b) the mode of fixation and subsequent preparatory procedures might alter the morphology of the Alzheimer's abnormal filaments.

Tau protein immunoreactivity in dementia of the Alzheimer type. I. Morphology, evolution, distribution, and pathogenetic implications.

The author has used two monoclonal antibodies against tau, Tau-1 and Tau-2, to study at the light microscopic level the morphology, evolution, and distribution of tau immunoreactivity in 21 cases with dementia of the Alzheimer type (DAT) with clinical histories of dementia ranging from 6 months to 10-15 years. They included four cases with Alzheimer's disease (AD), 14 cases with senile dementia of the Alzheimer type (SDAT), and three demented patients with Down's Syndrome (DS). The morphology and distribution of tau immunoreactivity was similar in all three forms of DAT, but the rapidity of evolution, as judged by the duration of dementia and the amount of immunoreactivity, was most severe in DS with dementia and least severe in SDAT. Excessive tau immunoreactivity, as compared with controls which were negative, was present in both astrocytes and vulnerable neurons. Tau-2-positive astrocytes were present throughout the brain and even in regions with no neuronal vulnerability. In evolving cases, several regions that in full-blown cases showed neuronal involvement contained only labeled astrocytes. The neurofibrillary tangles in neuronal involvement contained only labeled astrocytes. The neurofibrillary tangles in neuronal perikarya, the neurites in senile plaques, and an abundance of abnormal neurites found diffusely in the neuropil were intensely stained. In addition, stained granules (ribosomes) were present in both astrocytes and vulnerable neurons. The senile plaques frequently developed around and, on serial sectioning, were almost constantly associated with blood vessels. The amyloid core in senile plaques and the congophilic vessels were unstained. In cases with the shortest duration of dementia, tau immunoreactivity in neurons was found only in the amygdala, the subiculum, the Sommer's sector, the nucleus raphe dorsalis, locus ceruleus, and nucleus basalis of Meynert. In evolving cases, the depths of sulci were more severely affected than the crests of gyri, and the temporoparietal association cortex was more severely involved than the frontal cortex, but, in advanced cases, the depths of sulci, the crests of gyri, and the entire association cortex were equally affected.(ABSTRACT TRUNCATED AT 400 WORDS)

Phosphorylation determines two distinct species of Tau in the central nervous system.

The monoclonal antibody, Tau-1, which had previously been used to localize tau to the axonal compartment in brain has been reutilized for light and electron microscopic immunohistochemistry following phosphatase treatment of tissue. We report here that a significant quantity of tau in the central nervous system is phosphorylated in situ at or near the Tau-1 epitope, preventing the binding of the Tau-1 antibody. Upon removal of this/these phosphate group(s), however, Tau-1 was observed in the somatodendritic compartment of neurons as well as in axons. Furthermore, intense staining was also observed in astrocytes and in perineuronal glial cells. This immunoreactivity was present along the lengths of microtubules and on ribosomes (polysomes). Treatment of immunoblots of extracts of whole cerebral cortex with phosphatase confirmed the immunohistochemical results in that a 50-65% increase in Tau-1 binding to the tau region of the blot was noted. Moreover, a novel monoclonal antibody, Tau-2, was also used in these experiments. This antibody binds only to tau and localizes along microtubules in axons, somata, dendrites, and astrocytes and on ribosomes (polysomes) without phosphatase pretreatment.

Actin immunoreactivity localizes with segregated microtubules and membraneous organelles and in the subaxolemmal region in the beta,beta'-iminodipropionitrile axon.

Using the peroxidase-antiperoxidase staining technique with monoclonal and polyclonal antibodies against actin, we found that, in beta,beta'-iminodipropionitrile (IDPN)-treated axons, actin immunoreactivity was codistributed with segregated microtubules and membranous organelles in the central region and excluded from the peripheral axoplasm occupied by neurofilaments. Actin immunoreactivity was also present in the subaxolemmal region. Fast axonal transport is localized in the central region of the IDPN axon (Papasozomenos et al., 1982a). As both microtubules and actin are present in the central region of IDPN axons, a possible role of actin in fast axonal transport warrants further investigation.

Microtubule-associated protein 2 (MAP2) is present in astrocytes of the optic nerve but absent from astrocytes of the optic tract.

Using the peroxidase-antiperoxidase staining technique at the light- and electron-microscope levels and two monoclonal antibodies against microtubule-associated protein 2 (MAP2), we found that astrocytes located at the periphery of the rat optic nerve were strongly stained, while those in the central region were very weakly stained. MAP2 immunoreactivity was present in astrocytes of the optic chiasm, but was absent from astrocytes in the optic tract. Inside astrocytes, MAP2 immunoreactivity was excluded from bundles of glial filaments. Treatment of animals with beta,beta'-iminodipropionitrile (IDPN), which caused axonal atrophy, enhanced the staining intensity of all optic nerve astrocytes. Axons and oligodendrocytes remained unstained. Using PAGE and Western immunoblots, we found that extracts from bovine optic nerve contained MAP2. Astrocytes in any other region of the nervous system were negative for MAP2 immunoreactivity, except of the pituicytes and the astrocytes of the fimbria of hippocampus. The optic nerve, neurohypophysis, and hippocampal fimbria are white matter tracts that travel unsupported and free of surrounding nervous tissue. These findings suggest that MAP2 is expressed in astrocytes that are under excessive mechanical stress and further indicate that MAP2 may function as a cytoskeletal rigidifying agent in certain cells.

Characteristics of human medulloblastoma cell line TE-671 under different growth conditions in vitro: a morphological and immunohistochemical study.

The human medulloblastoma cell line, TE-671, was studied in vitro both in monolayer culture and in a three-dimensional culture system using gelfoam as the supporting matrix. Flow cytometry studies of cells grown in monolayer culture revealed a unimodal, tetraploid DNA content. Most cells in both in vitro systems contained neuron-specific enolase (NSE), actin, and tubulin, while only occasional cells or cell clusters contained the 68,000 molecular weight subunit of neurofilaments (NF mol. wt 68,000) or microtubule-associated protein 2 (MAP-2). In monolayer culture, long cellular processes containing NSE, NF mol. wt 68,000 and MAP-2, which were present at 2 days, were nearly absent by 7 days. All antigens were present at 4 days in the organ culture system; by 72 days, cells still stained positively for NF mol. wt 68 000 and MAP-2, but staining for NSE, actin, and beta-tubulin was diminished as compared to 4 days. Retinoic acid (RA) in the 13-cis isomer form at 10(-6) M was applied to monolayer cultures at day 1 for 6 days and to gelfoam cultures at day 1 for 28 days. RA did not significantly alter cell proliferation up to 7 days in vitro and did not appreciably affect cellular expression of NSE, NF mol. wt 68 000, MAP-2, beta-tubulin, or actin in either system. By electron microscopy, most cells grown under different culture conditions with or without RA treatment appeared to be undifferentiated and polygonal, with occasional cytoplasmic annulate lamellae. The immunohistochemical and ultrastructural features reported indicate that the TE-671 medulloblastoma line is composed primarily of primitive neuroepithelial cells with a limited potential for neuronal differentiation. This differentiation was not promoted by RA or by an in vitro system known to favour differentiation in a number of human and animal nervous system tumours. The findings suggest that the cells of the TE-671 line lack either receptors for retinoic acid or the capacity to respond to bound retinoic acid.