Association of PHB 1630 C>T and MTHFR 677 C>T polymorphisms with breast and ovarian cancer risk in BRCA1/2 mutation carriers: results from a multicenter study.

BACKGROUND: The variable penetrance of breast cancer in BRCA1/2 mutation carriers suggests that other genetic or environmental factors modify breast cancer risk. Two genes of special interest are prohibitin (PHB) and methylene-tetrahydrofolate reductase (MTHFR), both of which are important either directly or indirectly in maintaining genomic integrity. METHODS: To evaluate the potential role of genetic variants within PHB and MTHFR in breast and ovarian cancer risk, 4102 BRCA1 and 2093 BRCA2 mutation carriers, and 6211 BRCA1 and 2902 BRCA2 carriers from the Consortium of Investigators of Modifiers of BRCA1 and BRCA2 (CIMBA) were genotyped for the PHB 1630 C>T (rs6917) polymorphism and the MTHFR 677 C>T (rs1801133) polymorphism, respectively. RESULTS: There was no evidence of association between the PHB 1630 C>T and MTHFR 677 C>T polymorphisms with either disease for BRCA1 or BRCA2 mutation carriers when breast and ovarian cancer associations were evaluated separately. Analysis that evaluated associations for breast and ovarian cancer simultaneously showed some evidence that BRCA1 mutation carriers who had the rare homozygote genotype (TT) of the PHB 1630 C>T polymorphism were at increased risk of both breast and ovarian cancer (HR 1.50, 95%CI 1.10-2.04 and HR 2.16, 95%CI 1.24-3.76, respectively). However, there was no evidence of association under a multiplicative model for the effect of each minor allele. CONCLUSION: The PHB 1630TT genotype may modify breast and ovarian cancer risks in BRCA1 mutation carriers. This association need to be evaluated in larger series of BRCA1 mutation carriers.

Genetic polymorphisms in fatty acid metabolism genes and colorectal cancer.

Colorectal cancer (CRC) is a leading cause of cancer death worldwide. Epidemiological risk factors for CRC included dietary fat intake; consequently, the role of genes in the fatty acid biosynthesis and metabolism pathways is of particular interest. Moreover, hyperlipidaemia has been associated with different type of cancer and serum lipid levels could be affected by genetic factors, including polymorphisms in the lipid metabolism pathway. The aim of this study is to assess the association between single-nucleotide polymorphisms (SNPs) in fatty acid metabolism genes, serum lipid levels, body mass index (BMI) and dietary fat intake and CRC risk; 30 SNPs from 8 candidate genes included in fatty acid biosynthesis and metabolism pathways were genotyped in 1780 CRC cases and 1864 matched controls from the Molecular Epidemiology of Colorectal Cancer study. Information on clinicopathological characteristics, lifestyle and dietary habits were also obtained. Logistic regression and association analysis were conducted. Several LIPC (lipase, hepatic) polymorphisms were found to be associated with CRC risk, although no particular haplotype was related to CRC. The SNP rs12299484 showed an association with CRC risk after Bonferroni correction. We replicate the association between the T allele of the LIPC SNP rs1800588 and higher serum high-density lipoprotein levels. Weak associations between selected polymorphism in the LIPC and PPARG genes and BMI were observed. A path analysis based on structural equation modelling showed a direct effect of LIPC gene polymorphisms on colorectal carcinogenesis as well as an indirect effect mediated through serum lipid levels. Genetic polymorphisms in the hepatic lipase gene have a potential role in colorectal carcinogenesis, perhaps though the regulation of serum lipid levels.

Double heterozygosity in the BRCA1 and BRCA2 genes in the Jewish population.

BACKGROUND: The frequency and characteristics of disease in individuals who concomitantly harbor pathogenic mutations in both BRCA1 and BRCA2 genes are not established. MATERIALS AND METHODS: Data were collected from the database of Clalit Health Services National Familial Cancer Consultation Service. Probands referred to this clinical service and their family members are routinely tested for the three Jewish founder mutations (BRCA1: 185delAG, 5382insC, BRCA2: 6174delT). In addition, carriers identified in a population-based cohort of all cases diagnosed with breast cancer in Israel in 1987-1988 allowed the estimation of the population frequency of this phenomenon. RESULTS: In the clinic-based series of 1191 carriers of mutations in BRCA1 or BRCA2 belonging to 567 families, 22 males and females (1.85%) from 17 different families (3.0%) were found to harbor two different mutations. These included 18 individuals (1.51%) who concomitantly carried the 185delAG BRCA1 and the 6174delT BRCA2 mutations and four individuals (0.34%) who carried the 5382insC BRCA1 and the 6174delT mutations. All individuals were heterozygote carriers and none had a double mutation of both founder mutations in the BRCA1 gene itself. Seven of the 16 double carrier women (46.7%) had a personal history of breast carcinoma, diagnosed at a mean age of 44.6, compared with 372/926 (40.2%) carriers of a single mutation diagnosed with a mean age at diagnosis of 48.1 [odds ratio (OR)=1.3, 95% confidence interval (CI) 0.4-4.0]. One case (6.7%) had a personal history of ovarian carcinoma diagnosed at the age of 53 compared with 55/926 (5.9%) of the women with single mutation (OR=1.1, CI=0.2-7.6). The frequency of double mutations in the population-based national breast cancer cohort was 2.2% of all carriers, and 0.3% of all breast cancer cases in the Ashkenazi population in the cohort. The mean age at diagnosis of breast cancer was younger in the carriers of two mutations. CONCLUSION: Double carriers of mutations in the BRCA genes are rare and seem to be carrying a similar probability of developing breast and ovarian cancers as carriers of single mutations.

Evaluation of a candidate breast cancer associated SNP in ERCC4 as a risk modifier in BRCA1 and BRCA2 mutation carriers. Results from the Consortium of Investigators of Modifiers of BRCA1/BRCA2 (CIMBA).

BACKGROUND: In this study we aimed to evaluate the role of a SNP in intron 1 of the ERCC4 gene (rs744154), previously reported to be associated with a reduced risk of breast cancer in the general population, as a breast cancer risk modifier in BRCA1 and BRCA2 mutation carriers. METHODS: We have genotyped rs744154 in 9408 BRCA1 and 5632 BRCA2 mutation carriers from the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA) and assessed its association with breast cancer risk using a retrospective weighted cohort approach. RESULTS: We found no evidence of association with breast cancer risk for BRCA1 (per-allele HR: 0.98, 95% CI: 0.93-1.04, P = 0.5) or BRCA2 (per-allele HR: 0.97, 95% CI: 0.89-1.06, P = 0.5) mutation carriers. CONCLUSION: This SNP is not a significant modifier of breast cancer risk for mutation carriers, though weak associations cannot be ruled out.

The TP53 Arg72Pro and MDM2 309G>T polymorphisms are not associated with breast cancer risk in BRCA1 and BRCA2 mutation carriers.

BACKGROUND: The TP53 pathway, in which TP53 and its negative regulator MDM2 are the central elements, has an important role in carcinogenesis, particularly in BRCA1- and BRCA2-mediated carcinogenesis. A single nucleotide polymorphism (SNP) in the promoter region of MDM2 (309T>G, rs2279744) and a coding SNP of TP53 (Arg72Pro, rs1042522) have been shown to be of functional significance. METHODS: To investigate whether these SNPs modify breast cancer risk for BRCA1 and BRCA2 mutation carriers, we pooled genotype data on the TP53 Arg72Pro SNP in 7011 mutation carriers and on the MDM2 309T>G SNP in 2222 mutation carriers from the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA). Data were analysed using a Cox proportional hazards model within a retrospective likelihood framework. RESULTS: No association was found between these SNPs and breast cancer risk for BRCA1 (TP53: per-allele hazard ratio (HR)=1.01, 95% confidence interval (CI): 0.93-1.10, P(trend)=0.77; MDM2: HR=0.96, 95%CI: 0.84-1.09, P(trend)=0.54) or for BRCA2 mutation carriers (TP53: HR=0.99, 95%CI: 0.87-1.12, P(trend)=0.83; MDM2: HR=0.98, 95%CI: 0.80-1.21, P(trend)=0.88). We also evaluated the potential combined effects of both SNPs on breast cancer risk, however, none of their combined genotypes showed any evidence of association. CONCLUSION: There was no evidence that TP53 Arg72Pro or MDM2 309T>G, either singly or in combination, influence breast cancer risk in BRCA1 or BRCA2 mutation carriers.

Blastocystis hominis as a cause of hypoalbuminemia and anasarca.

The protozoan Blastocystis hominis has been considered nonpathogenic, but this classification has come under scrutiny in light of reports in the medical literature indicating it could be the cause of intestinal disorders and, in one case, hypoalbuminemia. Reported here is a severe case of infection with B. hominis that caused acute gastroenteritis with prolonged diarrhea, hypoalbuminemia and anasarca. The diagnosis was based on the parasitological finding, since no other pathological evidence was found. The patient responded favorably to treatment with metronidazole for 10 days. This case supports the idea that B. hominis should be considered as a cause of opportunistic infection in debilitated patients despite the controversy surrounding its pathogenicity.

Leprosy in Israel: an imported disease--the support of histopathological examination for its detection.

Leprosy is rare and non-endemic in Israel. Cases of leprosy are invariably imported by immigrants or foreign workers arriving from endemic areas. In view of the relative rarity of the disease, clinicians and pathologists are not always alert to the possibility of the disease or recognize potential symptoms. A case history is presented of a 31-year-old immigrant presenting symptoms of skin lesions and nodules on the hands and facial region, especially the ear lobe. Confirmation of the infection was provided by histopathology of suspected lesions stained for acid-fast bacilli (modified Fite-Faraco staining).

Laryngotracheobronchial involvement in a patient with nonendemic rhinoscleroma.

We report the first case of rhinoscleroma in an Israeli citizen, a former sailor with a transatlantic shipping company. Characteristic histologic changes from a tracheal biopsy and isolation of Klebsiella rhinoscleromatis from a blood culture after diagnostic bronchoscopy confirmed the diagnosis. Extreme delay in the diagnosis, a not uncommon feature in nonendemic areas, was associated with severe advanced laryngotracheobronchial disease. Treatment with quinolones was followed by significant improvement, but the patient died 1 month after presentation, apparently from upper airway obstruction.

Nuclear eukaryotic initiation factor 4E (eIF4E) colocalizes with splicing factors in speckles.

The eukaryotic initiation factor 4E (eIF4E) plays a pivotal role in the control of protein synthesis. eIF4E binds to the mRNA 5' cap structure, m(7)GpppN (where N is any nucleotide) and promotes ribosome binding to the mRNA. It was previously shown that a fraction of eIF4E localizes to the nucleus (Lejbkowicz, F., C. Goyer, A. Darveau, S. Neron, R. Lemieux, and N. Sonenberg. 1992. Proc. Natl. Acad. Sci. USA. 89:9612-9616). Here, we show that the nuclear eIF4E is present throughout the nucleoplasm, but is concentrated in speckled regions. Double label immunofluorescence confocal microscopy shows that eIF4E colocalizes with Sm and U1snRNP. We also demonstrate that eIF4E is specifically released from the speckles by the cap analogue m(7)GpppG in a cell permeabilization assay. However, eIF4E is not released from the speckles by RNase A treatment, suggesting that retention of eIF4E in the speckles is not RNA-mediated. 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB) treatment of cells causes the condensation of eIF4E nuclear speckles. In addition, overexpression of the dual specificity kinase, Clk/Sty, but not of the catalytically inactive form, results in the dispersion of eIF4E nuclear speckles.

Incidence of bacteraemia following fibreoptic bronchoscopy.

Guidelines for antibiotic prophylaxis of infective endocarditis prior to fibreoptic bronchoscopy, are based on only five studies, which showed a bacteraemia rate of <1% among 291 patients studied. T his study was designed to expand the current data regarding the frequency of bacteraemia following fibreoptic bronchoscopy. Aerobic and anaerobic cultures of venous blood and of lavage fluid were drawn from 200 consecutive patients undergoing fibreoptic bronchoscopy without respiratory infection or antibiotic treatment prior to the procedure. The true bacteraemia rate was calculated after excluding probable "contaminated" blood cultures. A possible correlation between type of procedure performed during the bronchoscopy and occurrence of bacteraemia was investigated. Positive blood cultures were noted following 26 bronchoscopy examinations. Coagulase negative Staphylococcus was found in the cultures of 18 patients, coagulase positive Staphylococcus in 3 patients, nonhaemolytic streptococci and a Klebsiella species in 2 patients each, and beta haemolytic streptococcus in one patient. After exclusion of 13 "contaminated" specimens the bacteraemia rate was 6.5% (13/200 patients). This study showed a bacteraemia rate of 6.5%, significantly higher than previously recognized in a cohort of patients undergoing fibreoptic bronchoscopy without either pulmonary infection or an unusually high rate of invasive procedures. These findings should be taken into account in future evaluations of recommendations for antibiotic prophylaxis of endocarditis.

Ectopic expression of 2-5A synthetase in myeloid cells induces growth arrest and facilitates the appearance of a myeloid differentiation marker.

Two variants of the human myeloid leukemia cell line HL-60 were used to study the possible involvement of the IFN-induced protein 2-5A synthetase in cell growth arrest and differentiation. The two variants, HL-205 and HL-525, are equally susceptible to differentiation to the granulocyte lineage by exposure to DMSO, but only HL-205 cells acquire the macrophage phenotype following exposure to phorbol esters. The kinetics of 2-5A synthetase activity was established in both variants exposed to either DMSO or phorbol 12-myristate 13-acetate. With DMSO treatment, 2-5A synthetase activity was markedly induced in both variants, although with slightly different kinetics. With phorbol 12-myristate 13-acetate treatment, 2-5A enzymatic activity increased only in HL-205; no activity was detected up to 96 h after treatment in HL-525. The induction of 2-5A synthetase activity is apparently alpha/beta-IFN dependent, because only antibodies directed against a mixture of alpha- and beta-IFN completely abolished the increase in activity detected during differentiation of HL-205 cells. To directly establish the role of 2-5A synthetase in differentiation, HL-205 cells were transfected with an expression vector harboring the cDNA for the 43-kDa isoform of murine 2-5A synthetase fused to the inducible metallothionein promoter. Two clones, clone 6, which yielded a low level of 2-5A synthetase activity in response to ZnCl2 (which activates the promoter), and clone 7, which was a high responder, were further analyzed and compared with the control clone, neo. Reductions in the rates of cell growth and thymidine incorporation were observed with both clone 6 and clone 7 cells exposed to ZnCl2; clone 7 was more responsive. In addition, the level of c-myc-specific RNA transcript was greatly reduced in ZnCl2 or beta-IFN-treated clone 7 cells, whereas the neo cells responded similarly only after beta-IFN treatment. Treatment of clone-neo cells with beta-IFN resulted in conversion of pRb protein from the phosphorylated to the underphosphorylated form within 24 h; ZnCl2 had no effect, even after 72 h. In contrast, the accumulation of the underphosphorylated form of pRb was observed in clone 7 cells treated either with beta-IFN or ZnCl2. Finally, a significant increase in nitro blue tetrazolium-positive cells, an indication of differentiation, was evident with ZnCl2-treated clone 6 and clone 7 cells; no such increase was observed with clone-neo cells under similar conditions. We conclude that ectopic expression of 2-5A synthetase in HL-205 cells results in cell growth arrest and facilitates the appearance of a myeloid differentiation marker.

Distinct sensitivity of normal and malignant cells to ultrasound in vitro.

The effect of ultrasonic irradiation on the viability of human normal (foreskin fibroblast and amniotic fluid epithelial) and tumor (breast carcinoma, melanoma, and lung carcinoma) cells lines was studied. Cells were subjected to ultrasonic irradiation with a frequency of 20 kHz and an intensity of 0.33 W/cm2 for variable periods of time. Several parameters were tested to determine the effects of ultrasonic irradiation on cell viability and cellular function. Normal cells were relatively resistant to ultrasonic irradiation, whereas malignant cells were much more sensitive. Maximum damage occurred 4 min after exposure of the malignant cells to irradiation. Cellular DNA and protein synthesis were significantly affected as a function of time of irradiation and cloning efficiency of malignant cells exposed to irradiation was greatly reduced. To generalize the consistency of the ultrasonic effect, studies on additional normal and malignant human cells of distinct origin are under way to test their sensitivity to ultrasonic irradiation. Thus, the applicability of ultrasonic irradiation as an antitumor agent may be important in the development of a new methodology in the treatment of cancer.

Functional domain analysis of interferon consensus sequence binding protein (ICSBP) and its association with interferon regulatory factors.

Interferon consensus sequence binding protein (ICSBP) is a member of the interferon regulatory factor (IRF) family of proteins that include IRF-1, IRF-2, and ISGF3gamma which share sequence similarity at the putative DNA binding domain (DBD). ICSBP is expressed exclusively in cells of the immune system and acts as a repressor of interferon consensus sequence (ICS) containing promoters that can be alleviated by interferons. In this communication, we have searched for functional domains of ICSBP by dissecting the DBD from the repression activity. The putative DBD of ICSBP (amino acids 1-121) when fused in frame to the transcriptional activation domain of the herpes simplex VP16 (ICSBP-VP16) is a very strong activator of ICS-containing promoters. In addition, ICSBP-VP16 fusion construct transfected into adenovirus (Ad) 12 transformed cells enabled cell surface expression of major histocompatibility complex class I antigens as did treatment with interferon. On the other hand, the DBD of the yeast transcriptional activator GAL4 was fused in frame to a truncated ICSBP in which the DBD was impaired resulting in a chimeric construct GAL4-ICSBP. This construct is capable of repressing promoters containing GAL4 binding sites. Thus, ICSBP contains at least two independent domains: a DBD and a transcriptional repressor domain. Furthermore, we have tested possible interactions between ICSBP and IRFs. The chimeric construct GAL4-ICSBP inhibited the stimulated effect of IRF-1 on a reporter gene, implying for a possible interaction between IRF-1 and ICSBP. Electromobility shift assays, demonstrated that ICSBP can associate with IRF-2 or IRF-1 in vitro as well as in vivo. Thus, ICSBP contains a third functional domain that enables the association with IRFs. These associations are probably important for the fine balance between positive and negative regulators involved in the interferon-mediated signal transduction pathways in cells of the immune system.

Hemoglobin is a late event in the differentiation of Friend erythroleukemic cells in-vitro. I. The role of interferon-induced proteins.

Here we report that the interferon (IFN)-induced proteins, 2'-5'-oligoadenylate synthetase (OAS) and IFN-induced protein kinase (PKI), appearance and activity precede that of hemoglobin (Hb) in the differentiation process of Friend erythroleukemic cells (FLC). Since our results are correlative, we assume that OAS and PKI are activated, and act at an early stage in the differentiation process, enabling the late onset of Hb synthesis. It is, thus, suggested that red blood cells harboring specific differentiating genes may be used as more efficient carriers of oxygen-binding molecules.

La autoantigen enhances and corrects aberrant translation of poliovirus RNA in reticulocyte lysate.

Translation initiation on poliovirus RNA occurs by internal binding of ribosomes to a sequence within the 5' untranslated region. We have previously characterized a HeLa cell protein, p52, that binds to a fragment of the poliovirus 5' untranslated region (K. Meerovitch, J. Pelletier, and N. Sonenberg, Genes Dev. 3:1026-1034, 1989). Here we report the purification of the HeLa p52. Protein microsequencing identified p52 as La autoantigen. The La protein is a human antigen that is recognized by antibodies from patients with autoimmune disorders such as systemic lupus erythematosus and Sjögren's syndrome. We show that the La protein stimulates translation of poliovirus RNA, but not brome mosaic virus, tobacco mosaic virus, and alfalfa mosaic virus 4 RNA, translation in a reticulocyte lysate. In addition, La corrects aberrant translation of poliovirus RNA in a reticulocyte lysate. Subcellular immunolocalization showed that La protein is mainly nuclear, but after poliovirus infection, La is redistributed to the cytoplasm. Our results suggest that La protein is involved in poliovirus internal initiation of translation and might function through a similar mechanism in the translation of cellular mRNAs.

ferT encodes a meiosis-specific nuclear tyrosine kinase.

ferT is a mouse testis-specific mRNA, shown previously to potentially encode a 51 kilodalton tyrosine kinase termed p51ferT. The accumulation of ferT RNA is restricted to primary spermatocytes that are at the prophase stage of the first spermatogenic meiotic division. By using antibodies raised against a synthetic peptide which was designed according to a putative p51ferT unique amino acid sequence, we have shown that testicular cells indeed contain a 51 kilodalton protein that is recognized by the anti-p51ferT antibodies. The protein was not detected in six nontesticular mouse tissues, nor was it detected, like the ferT RNA, in the testes of 14-day-old mice. These findings strongly suggest that the 51 kilodalton protein is p51ferT. Immunohistochemical staining localized p51ferT to meiotically dividing spermatocytes. Transfection experiments in CHO cells confirmed the nuclear localization of p51ferT in eukaryotic cells. p51ferT seems thus to be the first meiosis-specific nuclear tyrosine kinase described to date.

The response of normal and malignant cells to ultrasound in vitro.

The effect of ultrasonic irradiation on the viability of normal and tumor cell cultures derived from human and mouse origins was investigated. The cells were irradiated with a frequency of 2 MHz and intensity of 0.33 W/cm2, up to 4 min and immediately tested for cell viability using four different parameters: vital staining for the determination of the rate of cell growth; [3H]-thymidine and [3H]-leucine incorporation as an indication of the rate of DNA and protein synthesis respectively; and cloning efficiency as a measurement of the cell ability to multiply. Two human normal cell lines used in our studies, FS11 foreskin fibroblasts and Wish cells, were relatively resistant to ultrasonic irradiation effect although the growth rate of the latter was somewhat affected, particularly after 2 or 4 min of irradiation. However, cells derived from either malignant melanoma or breast carcinoma were highly sensitive to irradiation as demonstrated by a reduction of 96% and 65%, respectively, in cloning efficiency even after irradiation for 1 min. A third tumor cell line derived from lung carcinoma was more resistant. Two normal clones derived from NIH/3T3 mouse fibroblasts were used. These clones revealed some degree of sensitivity, particularly after 4 min of irradiation. However, their murine-sarcoma-virus transformed counterparts were found to be even more sensitive at identical times of ultrasonic irradiation, although the differences are not as striking as demonstrated with cells from human origin.(ABSTRACT TRUNCATED AT 250 WORDS)

A fraction of the mRNA 5' cap-binding protein, eukaryotic initiation factor 4E, localizes to the nucleus.

The 5' cap structure m7GpppN (where N is any nucleotide) is a ubiquitous feature of cellular eukaryotic mRNAs. The cap is multifunctional as it is involved in translation, nucleocytoplasmic transport, splicing, and stabilization of mRNA against 5' exonucleolytic degradation. The cap binding protein, eukaryotic initiation factor 4E (eIF-4E), is a translation initiation factor that binds to the cap structure and is part of a complex (eIF-4F) that promotes mRNA binding to ribosomes. Overexpression of eIF-4E in fibroblasts results in cell transformation. To test the hypothesis that some of the biological effects of eIF-4E might be effected by a nuclear function, we determined the cellular distribution of eIF-4E. By means of indirect immunofluorescence experiments using polyclonal and monoclonal antibodies against eIF-4E as well as transfected epitope-tagged eIF-4E, we demonstrate that a fraction of eIF-4E localizes to the nucleus. These results suggest that eIF-4E is also involved in a nuclear function.

Biological effects of photoactivated-HPD and cholesteryl hemisuccinate on erythroid differentiation.

In order to establish the ability of porphyrins to distinguish between differentiated and undifferentiated cells of the erythropoietic pathway, the cytotoxic effects of hematoporphyrin derivative (HPD) on Friend erythroleukemic cells (FLC) were derivative (HPD) on Friend erythroleukemic cells (FLC) were studied. Since cholesterol affects the fluidity of cell membranes, the inhibitory effect of cholesteryl hemisuccinate (CHS) on HPD was similarly tested. FLC were induced with either dimethyl sulfoxide (DMSO), hemin, or both. The cells responded to DMSO-treatment by the synthesis of a large amount of hemoglobin and a decrease in both the cell volume and rate of cell-growth. Hemin, on the other hand, did not drive FLC to synthesize hemoglobin and reduced only moderately the growth rate compared to untreated cultures. The combined effect of DMSO and hemin led to a profound inhibition of the growth rate, but did not increase the synthesis of hemoglobin compared to the level observed in cells treated with DMSO only. The binding property of HPD to FLC was also determined. DMSO-treatment significantly reduced the amount of HPD-binding, and combined treatment with DMSO and hemin resulted in even a lower level of HPD-binding. On the other hand, induced as well as non-induced cells showed the same sensitivity to photoactivated HPD when both DNA and protein synthesis were examined. Pretreatment of both differentiated and undifferentiated cells with CHS reduced the cytotoxicity of photoactivated HPD to the same level. We conclude that the decreased binding of HPD to differentiated cells is a result of a reduction in their cell volume. Thus, the differentiation process per se does not protect cells against the photodynamic effect of HPD. Moreover, CHS may act as a scavenger or first acceptor of singlet oxygen blocking the photodynamic effect.