Hispanic/Latinos and non-Hispanic whites' childhood cancer survivors and parents: a dyadic analysis of coping resources and mental health

PURPOSE

While limited, dyadic research demonstrates the interdependent relationship between the health and adjustment after treatment between cancer survivors and caregivers. We examined interrelationships between coping resources and mental health among childhood cancer survivors (CCS)-parent dyads.

METHODS

One hundred sixty CCS-parent dyads from the Project Forward pilot study completed validated questions assessing social support, religiosity, spirituality, depressive symptoms, and perceived stress. Bidirectional associations were identified with path analysis utilizing the actor-partner interdependence model (APIM). We used a multigroup approach to test for the moderating effects by Hispanic ethnicity on these relationships.

RESULTS

Mean age of CCS was 20 years old, 51% female, 30% diagnosed with leukemia, and mean of 7 years from diagnosis. The mean age of parents was 49 years old and 89% were mothers. For both CCS and parents, perceived social support was inversely associated with their depressive symptoms and perceived stress (e.g., actor effects). Parents' social support was not significantly associated with CCS's depressive symptoms and stress. However, higher perceived social support by the CCS was inversely associated with parents' depressive symptoms (β =  - 0.202, p < 0.01) and perceived stress (β =  - 0.164, p < 0.05) (e.g., partner effects). Additional actor effects were observed between spirituality, religiosity, and depressive systems when we explored the moderating effects of Hispanic ethnicity.

CONCLUSION

Partner effects of social support among CCS-parent dyads may influence psychological distress.

IMPLICATION FOR CANCER SURVIVORS

Our findings on parent-child associations between social support and psychosocial well-being imply that survivorship care can be enhanced when the social support needs of both survivors and their parents are addressed together.

A Novel Discriminating Tool for Microcytic Anemia in Childhood

Accurate and timely interpretation of microcytic anemia can be diagnostically challenging in the primary care setting. We sought to develop a novel model for distinguishing iron-deficiency anemia from thalassemia trait in the modern pediatric population. Demographic history and red blood cell indices were retrospectively characterized for 76 children referred to our pediatric hematology clinic for evaluation of microcytic anemia. Statistically significant variables were sequentially added into a logistic regression model to develop the final model. The final discriminating model incorporates red cell distribution width, mean corpuscular hemoglobin concentration, and red blood cell values. Favorable predictive performance is seen in the initial (sensitivity 89.2%, specificity 92.3%) and external validation cohort (sensitivity 84.4%, specificity 88.9%). This novel tool may aid in determining the cause of hypochromic, microcytic anemia in the primary care setting. Finally, the study cohort reflects an underrepresented group in the development of screening tools, and thus offers generalizability.

Social support experiences of hispanic/latino parents of childhood cancer survivors in a safety-net hospital: a qualitative study

PURPOSE

To describe the social support experiences of Hispanic/Latino parents while caregiving for childhood cancer survivors.

RESEARCH APPROACH

Semi-structured one-on-one interviews were conducted among 15 caregivers from a safety-net hospital in Los Angeles. A thematic analysis approach was used to analyze data.

FINDINGS

The positive influence of social support throughout their caregiving experience included (1) sharing information-enhanced knowledge, (2) receiving comfort and encouragement, (3) receiving tangible assistance reducing the caregiving burden, and (4) enhancing caregiving empowerment/self-efficacy. Sub-themes regarding the lack of social support included (1) being a single parent and (2) family and friends withdrawing after the child's cancer diagnosis.

CONCLUSION

We found Hispanic/Latino parents strongly value social support as it enables them to have essential resources that support caregiving for their child and themselves. Efforts should ensure that caregivers are routinely screened to identify their supportive needs so that support services for caregivers can be optimized and tailored, as those with a lack of social support may experience excessive caregiver burden.

Understanding Delayed Presentation to Emergency Care in Pediatric Patients With Neutropenic Fever

We investigated social and logistic factors eg, distance from the medical center, language barriers, other children to care for, number of caregivers, etc.) for families to delay seeking immediate emergency care for neutropenic fever in a retrospective cohort study of all pediatric hematology-oncology patients who presented for fever in the setting of neutropenia to our emergency department or clinic from 2015 to 2020. Patients with a history of at least 2 prior admissions for neutropenic fever waited more often for a second fever before presenting versus those without such history (odds ratio 5.00, 95% CI 1.26 to 19.84, P =0.04). No other significant associations were found.

Psychological Impact and Coping Strategies of Hispanic Parents of Children with Cancer: A Qualitative Study

Throughout the cancer trajectory, parents of childhood cancer survivors (CCSs) may experience mental and social challenges requiring continual adaptation to cancer-induced stress. Using Lazarus and Folkman's Transactional Model of Stress and Coping framework, this qualitative study aimed to describe Hispanic parents' psychological health and explore their coping strategies. Purposive sampling was used to recruit 15 Hispanic caregivers from a safety-net hospital in Los Angeles County. To be eligible, participants had to be: the primary caregiver of a CCS who had completed active treatment, the primary caregiver or child self-identified as Hispanic, and proficient in English or Spanish. The interviews lasted approximately 60 min, were audio-recorded (in English and Spanish), and professionally transcribed. Data were analyzed following a thematic content analysis with deductive and inductive approaches on Dedoose. Participants described high levels of stress and fear when their child was diagnosed with cancer. They also shared experiencing symptoms of social anxiety, post-traumatic stress disorder, and depression. Participants' coping strategies were encompassed by three major themes: problem-focused, emotion-focused, and avoidant coping strategies. Problem-focused coping strategies included self-efficacy, behavioral change, and social support. Emotion-focused coping strategies included religious practices and positive reframing. Avoidant coping strategies included denial and self-distraction. Despite the evident disparities in psychological health for Hispanic parents of CCSs, gaps remain in designing a culturally tailored program to help alleviate the caregiver burden. This study provides insights regarding coping strategies that Hispanic caregivers use to deal with the psychological impact of their child's cancer diagnosis. Our findings also delve into the contextual and cultural factors that impact psychological adjustment.

Survival of pediatric Hodgkin lymphoma patients treated with doxorubicin, bleomycin, vincristine, etoposide, prednisone, and cyclophosphamide (ABVE-PC) versus doxorubicin, bleomycin, vinblastine, and dacarbazine (ABVD) at a single institution

BACKGROUND

Adriamycin, bleomycin, vinblastine, dacarbazine (ABVD), the de facto standard of care in adult-onset Hodgkin lymphoma (HL), has not been directly compared to doxorubicin, bleomycin, vincristine, etoposide, prednisone, and cyclophosphamide (ABVE-PC), a pediatric-aimed regimen designed to reduce late effects. We aimed to describe the single-institution experience of using both regimens in patients with pediatric HL.

METHODS

This retrospective cohort study evaluated a total of 224 patients diagnosed with HL between 1999 and 2018 at Children's Hospital Los Angeles (CHLA), of which 93 patients were eligible having received ABVD (n = 46) or ABVE-PC (n = 47) chemotherapy as their initial treatment. Descriptive analyses were performed using the Student's t-test or Fisher's exact test. Survival analysis used the Kaplan-Meier method. Events included death, relapse, and secondary malignancy. We also describe the use of radiation therapy, pulmonary toxicity, and cardiomyopathy determined by shortening fraction <29%. Analyses followed an intention-to-treat principle.

RESULTS

There was no difference in baseline characteristics between the patients receiving ABVE-PC or ABVD in regard for stage, risk group, or prognostic variables, such as the presence or absence of "B" symptoms, bulky disease, and extra-nodal involvement. A greater proportion of patients treated with ABVE-PC received consolidating external beam radiation treatment (XRT) either by randomization or by response compared to ABVD (59.6% vs. 32.6%, respectively, p = .01). While not statistically significant, response to therapy, assessed by positron emission tomography/computerized tomography (PET/CT) where available, mirrored the use for radiation (rapid response 58.3% vs. 90.0%, n = 34, p = .11). The median dose of anthracycline (doxorubicin) was the same in patients receiving ABVE-PC versus ABVD (200 vs. 200 mg/m² , interquartile range 200-250 vs. 200-300 mg/m² , p = .002). There was no difference in event-free survival (p = .63) or overall survival (p = .37) with a median follow-up length of 3.9 years.

CONCLUSIONS

ABVD and ABVE-PC achieved similar survival outcomes in our single-institution cohort.

The Impact of Hispanic Ethnicity and Language on Communication Among Young Adult Childhood Cancer Survivors, Parents, and Medical Providers and Cancer-Related Follow-Up Care

PURPOSE

The triad of communication between young adult childhood cancer survivors (YACCSs), their parents, and their medical providers is an important process in managing health care engagement. This study sought to identify communication patterns among this triad, factors associated with communication, and engagement of survivorship care.

METHODS

We analyzed data from Project Forward, a population-based study that surveyed YACCSs and their parents. YACCSs were on average age 20 years, 7 years from diagnosis, 50% female, and 57% identified as Hispanic/Latino (N = 160 dyads). Latent class analysis of nine communication indicators from parent and YACCS surveys identified distinct classes of communication between YACCSs, parents, and medical providers. Associations between resulting classes and YACCS/parent characteristics were examined using multinomial logistic regression. Logistic regression was used to examine the association between communication classes and cancer-related follow-up care.

RESULTS

Latent class analysis identified three classes of triad communication: (1) high health care-focused communication (37.5%), (2) high comprehensive communication (15.6%), and (3) overall low communication (46.9%). After adjusting for covariates, greater time since diagnosis was associated with reduced odds of membership in class 2 while dyads with Spanish-speaking Hispanic parents were more likely to be in class 2 (v class 3). Additionally, YACCSs who were in either of the high communication groups were more likely to have received recent follow-up care.

CONCLUSION

Examining language preference provides an important contextual understanding as we found Spanish-speaking Hispanic parents engaged in high communication, which was associated with cancer-related follow-up care. Yet, our results also support the need to enhance communication between this triad to improve outcomes.

Effect of childhood obesity on admissions for respiratory disease

AIM

The purpose of this study was to assess for an association between higher body mass index and disease severity, morbidity and mortality in children admitted for an acute respiratory distress and failure.

METHODS

A single-institution retrospective cross-sectional study performed in the United States evaluating paediatric patients, 2-20 years of age, admitted for diagnoses related to acute respiratory distress and acute respiratory failure. Main outcomes include disease severity as assessed using the respiratory component of the Paediatric Early Warning Score (PEWS) with adjustment for altered mental status (Resp-PEWS + AMS), hospital or intensive care length of stay (LOS) and death.

RESULTS

Children with obesity made up 42/334 (13%) of the cohort. There was no significant difference in Resp-PEWS + AMS between obese and non-obese cohorts (mean of 0.93, {standard deviation 1.11} vs. 1.13 {1.35}, range 0-6, rank sum p = 0.46). There was no significant difference in overall hospital LOS or intensive care LOS. Multivariate analysis including diagnosis as a control variable did not change the results.

CONCLUSION

We found that body habitus was not an independent factor for illness severity or clinical outcomes.

Abstract PO-016: A latent class analysis of communication patterns between Hispanic and non-Hispanic childhood cancer survivors, parents, and medical providers

Introduction: The triad of communication between childhood cancer survivors (CCS), their parents, and their medical providers may motivate CCS healthcare engagement but has not been examined. This may be particularly important for Hispanic/Latino populations, who are more likely to trust and receive health information from hospital providers and are less likely to remain engaged in survivorship care compared to non-Hispanic white persons. Methods: We analyzed data from the Project Forward pilot study, a population-based study that evaluated follow-up care among 160 CCS-parent dyads (CCS mean age=20 years, 7 years from diagnosis, and 29% of parents identified as Spanish-speaking Hispanic). Nine indicators representing multiple dimensions of communication were used in latent class analysis to identify distinct classes of communication. These indicators were selected from the parent and CCS survey and asked about communication between CCS, parents, and medical providers. The association between resulting classes and various covariates (e.g., parent ethnicity/language, CCS demographic, clinical characteristics) was examined using multinomial logistic regression. Results: Three classes of the triad of communication were identified: (1) high healthcare-focused communication (37.5%); (2) high comprehensive communication (15.6%); and (3) overall low communication (46.9%). The high healthcare-focused communication class was characterized by patterns of high probability for communication about future health care needs among CCS, parents, and medical providers. The high comprehensive communication class was characterized by a high probability of communication about future healthcare needs and a high probability for parent-CCS communication about different cancer facets. The overall low communication class was characterized by a low probability of endorsing any communication items. Greater time since diagnosis was marginally significantly associated with reduced odds of the dyad's membership in class 2 [OR=0.798, 95% CI=0.635, 1.002, p-value=0.0520], compared to class 3 (low communication). Additionally, dyads with English-speaking non-Hispanic parents were less likely to be in class 2 [OR=0.361, 95% CI=0.130, 1.005, p-value=0.0511], compared to class 3. After adjusting for all covariates simultaneously, greater time since diagnosis was associated with reduced odds of membership in class 2 (vs class 3). Dyads with Spanish-speaking Hispanic parents were more likely to be in classes 1 and 2 (vs. class 3). Discussion: Our results support the need to enhance communication among CCS, parents, and medical providers generally to improve knowledge and understanding about the long-term effects of cancer, treatment, and outcomes. Our study suggests that dyads, where parents were Spanish-speaking Hispanics tended to engage in high communication. Examining language preference provides an important contextual understanding as it supports the notion that Hispanic/Latino cultural values may play a favorable role in high levels of communication.

Citation Format: Carol Y. Ochoa, Junhan Cho, Kimberly A. Miller, Lourdes Baezconde-Garbanati, Randall Y. Chan, Albert J. Farias, Joel E. Milam. A latent class analysis of communication patterns between Hispanic and non-Hispanic childhood cancer survivors, parents, and medical providers [abstract]. In: Proceedings of the AACR Virtual Conference: 14th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2021 Oct 6-8. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2022;31(1 Suppl):Abstract nr PO-016.

Post-Chemotherapy Histiocyte-Rich Pseudotumors: Radiologic and Endoscopic Mimics of Residual Lymphoma

Development of post-chemotherapy histiocyte-rich pseudotumor (PHP) is an underrecognized event following therapy in lymphoma patients and may mimic residual tumor using current therapy monitoring protocols. We report a series of 5 patients with PHP along with a review of the literature. In our series, we describe 3 patients with persistent hypermetabolic masses by positron emission tomography-computed tomography, one with persistent terminal ileal nodules on endoscopy, and one with bone marrow involvement, a site not associated with mass-like disease. Twenty-three patients with long-term follow-up were identified from our series and review of the literature. Forty-four percent of patients received additional therapy, and only 4% of patients died of lymphoma. This study illustrates that PHPs are not identified using current lymphoma therapy monitoring algorithms and may result in overtreatment with risk for additional therapy-related complications. The need for confirmatory tissue biopsy in this setting is recommended.

Combined immune checkpoint blockade increases CD8+CD28+PD-1+ effector T cells and provides a therapeutic strategy for patients with neuroblastoma

Immune checkpoint therapy has resulted in minimal clinical response in many pediatric cancers. We sought to understand the influence of immune checkpoint inhibition using anti-PD-1 and anti-CTLA-4 antibodies individually, in combination, and after chemotherapy on immune responses in minimal and established murine neuroblastoma models. We also sought to understand the role of the tumor microenvironment (TME) and PD-L1 expression and their alteration post-chemotherapy in our models and human tissues. PD-L1 expression was enriched in human tumor-associated macrophages and up-regulated after chemotherapy. In a murine minimal disease model, single and dual immune checkpoint blockade promoted tumor rejection, improved survival, and established immune memory with long-term anti-tumor immunity against re-challenge. In an established tumor model, only dual immune checkpoint blockade showed efficacy. Interestingly, dual immune checkpoint therapy distinctly influenced adaptive and innate immune responses, with significant increase in CD8⁺CD28⁺PD-1⁺ T cells and inflammatory macrophages (CD11b^hiCD11c⁻F4/80⁺Ly6C^hi) in tumor-draining lymph nodes. Adding chemotherapy before immunotherapy provided significant survival benefit for mice with established tumors receiving anti-PD-1 or dual immune checkpoint blockade. Our findings demonstrate anti-PD-1 and anti-CTLA-4 therapy induces a novel subset of effector T cells, and support administration of induction chemotherapy immediately prior to immune checkpoint blockade in children with high-risk neuroblastoma.

Acceptability of assisted reproductive technologies in Hong Kong, a very low fertility Asian city

Background

Although advances in medical technologies now allow greater reproductive options, the social acceptance of assisted reproductive technologies (ART) has not been examined in East Asian countries which currently have the lowest fertility rates in the world and highly prohibitive regulations.

Methods

A cross-sectional telephone surveys interviewed 990 among Hong Kong Chinese adults (&gt;18 years of age) in 2015 who were asked about their knowledge and attitudes towards various ART and their inclination to use ART. A focus group was conducted (n = 30) on physicians to examine the perceived barriers and benefits of integrating ART as routine offerings.

Results

Although nearly all adults (&gt;92.0%) were familiar with ART procedures such as in vitro fertilization, sperm banking, and gestational surrogacy, attitudes supporting the use of these services and the inclination to use these services varied widely by socio-demographic attributes. Nearly one-third (31.5%) of women said that they would consider cryopreservation of their oocytes or embryos if they could afford it and 21.9% would encourage their female family members to do so. Although respondents considered sperm donation and embryo preservation to be well-accepted practices, support for these services was noticeably lower than in Western countries for unmarried individuals and homosexuals. Also, the vast majority of respondents were much more disinclined to use anonymous donor gametes than in Western countries. Among medical practitioners, the primary barriers to routine offering of these services to their clients was the perceived lack of cultural acceptance of these types of services.

Conclusions

Public support of assisted reproductive services for genetic offspring is well-accepted for heterosexual couples. Main Messages: Asian countries with sub-replacement fertility levels may consider integrating ART into their mainstream health services and updating their regulatory frameworks.

Key messages

Public support for assisted reproductive technologies is high for married couples only in Hong Kong. Given the sub-replacement fertility levels, cities in East Asia should consider updating regulatory frameworks to allow expansion of ART services.

Tumor-associated macrophages promote neuroblastoma via STAT3 phosphorylation and up-regulation of c-MYC

Tumor-associated macrophages (TAMs) are strongly associated with poor survival in neuroblastomas that lack MYCN amplification. To study TAM action in neuroblastomas, we used a novel murine model of spontaneous neuroblastoma lacking MYCN amplification, and observed recruitment and polarization of TAMs, which in turn enhanced neuroblastoma proliferation and growth. In both murine and human neuroblastoma cells, we found that TAMs increased STAT3 activation in neuroblastoma cells and transcriptionally up-regulated the MYC oncogene. Analysis of human neuroblastoma tumor specimens revealed that MYC up-regulation correlates with markers of TAM infiltration. In an IL6^ko neuroblastoma model, the absence of IL-6 protein had no effect on tumor development and prevented neither STAT3 activation nor MYC up-regulation. In contrast, inhibition of JAK-STAT activation using AZD1480 or the clinically admissible inhibitor ruxolitinib significantly reduced TAM-mediated growth of neuroblastomas implanted subcutaneously in NOD scid gamma mice. Our results point to a unique mechanism in which TAMs promote tumor cells that lack amplification of an oncogene common to the malignancy by up-regulating transcriptional expression of a distinct oncogene from the same gene family, and underscore the role of IL-6-independent activation of STAT3 in this mechanism. Amplification of MYCN or constitutive up-regulation of MYC protein is observed in approximately half of high-risk tumors; our findings indicate a novel role of TAMs as inducers of MYC expression in neuroblastomas lacking independent oncogene activation.

Ocular Whipple's disease: earlier definitive diagnosis

PURPOSE

Whipple's disease is a rare, chronic, and multiorgan bacterial disease that predominantly involves the gut and its lymphatic drainage in middle-aged Caucasian men but may involve the eye. It is often difficult to diagnose and treat. We report results of one more polymerase chain reaction (PCR) analysis-diagnosed ocular Whipple's disease (OWD) case and the care of three new patients with ocular inflammation caused by OWD.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS

Three patients.

METHODS

Diagnostic PCR was performed on a vitreous sample, medical records of three patients with OWD were reviewed, and a literature review (1907 to present) located 74 OWD cases. Analysis of published OWD cases to seek out factors that contribute to earlier, definitive diagnosis and treatment of OWD is made.

MAIN OUTCOME MEASURES

Response of ocular inflammation and vision to treatment.

RESULTS

One of 3 new and 4 of 74 published OWD cases reviewed were diagnosed with PCR on vitreous samples and subsequently successfully treated with antibiotics without devastating central nervous system (CNS) sequelae.

CONCLUSION

Diagnostic PCR on vitreous samples and recognition of key presenting symptoms in patients with OWD allows earlier definitive diagnosis, when the disease may be more amenable to antibiotic treatment, compared with "late" CNS Whipple's disease in the cases reviewed.

A reporter gene assay for the detection of phytoestrogens in traditional Chinese medicine

Bupleurum & Peony Formula (Jia Wei Xiao Yao San) is a herbal formula which possesses a clinical history for the treatment of menopausal syndrome and menstrual irregularity. The present investigation reports the ability to monitor the formula's phytoestrogen content that will allow for the implementation of a standardization protocol that is based on a quantifiable biological response. Utilizing an oestrogen-sensitive chimeric receptor/reporter gene element which has been stably transfected into HeLa cells, the botanical formula was shown to induce the expression of the reporter gene, luciferase, in a dose dependent manner. Pretreatment of the HeLa cells with the botanical formula produced a 5-fold increase in bioluminescence compared with the control. Additionally, our studies showed that the response of the cells, when challenged by the botanical formula, was oestrogen specific. Pretreatment of the cells with tamoxifen effectively blocked the activation of the chimeric oestrogen receptor by the botanical formula. The cell line provides a sensitive assay that can easily detect the presence of phytoestrogens in complex botanical formulas.

Role of intronic E- and N-box motifs in the transcriptional induction of the acetylcholinesterase gene during myogenic differentiation

In this study, we examined whether an intronic N-box motif is involved in the expression of acetylcholinesterase (AChE) during myogenesis. We determined that AChE transcripts are barely detectable in cultured myoblasts and that their levels increase dramatically in myotubes. Nuclear run-on assays revealed that this increase was accompanied by a parallel induction in the transcriptional activity of the AChE gene. These changes in transcription were also observed in transfection experiments using AChE promoter-reporter gene constructs. Mutation of the intronic N-box at position +755 base pairs (bp) reduced by more than 70% expression of the reporter gene in myotubes. Disruption of an adjacent E-box, at position +767 bp, also reduced expression of the reporter gene following myogenic differentiation. Co-transfection experiments using AChE promoter-reporter gene constructs and a myogenin expression vector showed that expression of this regulatory factor increased expression of the reporter gene in myotubes. Although the AChE promoter contains multiple E-boxes, mutation of this intronic one was sufficient to prevent the myogenin-induced increase in reporter gene expression. Together, these results indicate that changes in AChE gene transcription occur during myogenesis and highlight the contribution of the intronic N- and E-box motifs in the developmental regulation of the AChE gene in skeletal muscle.

Molecular mechanisms underlying the activity-linked alterations in acetylcholinesterase mRNAs in developing versus adult rat skeletal muscles

The molecular mechanisms underlying the activity-linked plasticity of acetylcholinesterase (AChE) mRNA levels in mammalian skeletal muscle have yet to be established. Here, we demonstrate that denervation of adult muscle induces a dramatic (up to 90%) and rapid (within 24 h) decrease in the abundance of AChE mRNAs. By contrast, denervation of 14-day-old rats leads to a significantly less pronounced reduction (50% of control) in the expression of AChE mRNAs. Assessment of the transcriptional activity of the AChE gene reveals that it remains essentially unchanged in adult denervated muscles, whereas it displays an approximately two- to three-fold increase (p < 0.05) in denervated muscles from 2- to 14-day-old rats. In addition, we observed a higher rate of degradation of in vitro transcribed AChE mRNAs upon incubation with protein extracts from denervated muscles. Finally, UV-crosslinking experiments reveal that denervation increases the abundance of RNA-protein interactions in the 3' untranslated region of AChE transcripts. Taken together, these data suggest that the abundance of AChE transcripts in mature muscles is controlled primarily via posttranscriptional regulatory mechanisms, whereas in neo- and postnatal muscles, both transcriptional and posttranscriptional regulation appears critical in dictating AChE mRNA levels. Accordingly, the activity-linked transcriptional regulation of the AChE gene appears to demonstrate a high level of plasticity during muscle development when maturation of the neuromuscular junctions is still occurring.

Distances between DNA and ATP binding sites in the TyrR-DNA complex

The Escherichia coli regulatory protein TyrR controls the expression of eight transcription units that encode proteins involved in the biosynthesis and transport of aromatic amino acids. It binds to DNA as a homodimer with a subunit molecular mass of 57 640 Da, each of which has a single site for the binding of ATP within a central structural domain. This paper reports distances between four sites on the DNA and the ATP binding site as determined by fluorescence resonance energy transfer. The DNA was a 30mer containing a centrally located binding site for TyrR. Replacement of a thymidine residue with an aminouridine residue at positions -9, -7, -3, and 2 of the palindromic oligonucleotide sequence enabled the placement of a single fluorescein group along the major groove of the DNA. The energy transfer acceptor was ATP labeled with a rhodamine group through positions 2' and 3' of the ribose, positions that are known to cause minimal interference with the binding of ATP to protein. The dissociation constant for the binding of rhodamine-ATP to TyrR was 300 nM as determined by steady-state fluorescence anisotropy titrations. The energy transfer efficiencies were determined by measuring the level of quenching of donor fluorescence on binding rhodamine-ATP to the TyrR-DNA complex. The experimental transfer efficiencies were compared to theoretical values calculated for a model of the DNA-TyrR complex in which the position of the ATP binding site was allowed to vary over the surface of the monomer unit. Theory was written to account for the transfer from one donor to two acceptors, one on each monomer unit of the TyrR dimer. The results indicate that the ATP binding site is about 40-45 A from the nearest point on the DNA and distant from the DNA helix-turn-helix binding domain. The effects of ATP binding of (i) increasing the TyrR binding affinity by a factor of 4-5 and (ii) permitting the binding of the tyrosine corepressor must therefore occur because of a significant allosteric change in the conformation of the protein.

Chronic activation of ORL1 receptor induces supersensitization of adenylyl cyclase

The opioid receptor-like (ORL1) receptor regulates a variety of effectors shared by its close relatives, the opioid receptors. Supersensitization of adenylyl cyclase (AC) is a hallmark of cellular tolerance induced by chronic activation of opioid receptors. To examine if chronic activation of the ORL1 receptor leads to a similar adaptation, a HEK293 cell line stably expressing the human ORL1 receptor (293/ORL1) was established. Chronic treatment of 293/ORL1 cells with nociceptin/OFQ resulted in enhanced AC activity in response to forskolin stimulation. The AC supersensitivity was blocked by pertussis toxin, indicating the involvement of Gi/Go proteins. Likewise, chronic activation of endogenous ORL1 receptors in the neuroblastoma SK-N-SH cells led to Gi/Go-mediated AC supersensitization.

The role of antibody to human beta4 integrin in conjunctival basement membrane separation: possible in vitro model for ocular cicatricial pemphigoid

PURPOSE

To demonstrate the specific binding of autoantibodies present in the sera of patients with ocular cicatricial pemphigoid (OCP) to human beta4 integrin present in the normal human conjunctiva (NHC) and to study the role of OCP autoantibodies and antibody to human beta4 integrin in the pathogenesis of subepithelial lesion formation in OCP.

METHODS

Indirect immunofluorescence assay and in vitro organ culture method using NHC were used. Sera and IgG fractions from 10 patients with OCP; immunoaffinity-purified OCP autoantibody; antibodies to human beta4, beta1, alpha6, and alpha5 integrins; and sera from patients with pemphigus vulgaris, bullous pemphigoid (BP), and chronic atopic and chronic ocular rosacea cicatrizing conjunctivitis; and normal human serum (NHS) were used.

RESULTS

Nine of 10 OCP sera or IgG fractions, immunoaffinity-purified OCP autoantibody, antibodies to human beta4 and alpha6 integrins, and sera from patients with BP showed homogenous, smooth linear binding along the basement membrane zone (BMZ) of the NHC. NHS, antibodies to other integrins, and sera from patients with chronic cicatrizing conjunctivitis from other causes showed no such binding. When NHC was first absorbed with OCP sera and then reacted with anti-beta4 antibodies or vice versa, the intensity of the BMZ binding was dramatically reduced or completely eliminated, indicating that there were autoantibodies in OCP sera specific for the beta4 integrin. BMZ separation developed 48 to 72 hours after addition of total OCP sera, IgG fractions from OCP sera, immunoaffinity-purified autoantibodies from sera of patients with OCP, or anti-beta4 antibodies to the NHC cultures, but not after addition of normal control sera, sera from patients with chronic cicatrizing conjunctivitis from causes other than OCP, or sera from patients with OCP in clinical remission.

CONCLUSION

Circulating anti-beta4 integrin antibody may have an important role in the pathogenesis of OCP.

An intronic enhancer containing an N-box motif is required for synapse- and tissue-specific expression of the acetylcholinesterase gene in skeletal muscle fibers

mRNAs encoding acetylcholinesterase (AChE; EC 3.1.1.7) are highly concentrated within the postsynaptic sarcoplasm of adult skeletal muscle fibers, where their expression is markedly influenced by nerve-evoked electrical activity and trophic factors. To determine whether transcriptional regulatory mechanisms account for the synaptic accumulation of AChE transcripts at the mammalian neuromuscular synapse, we cloned a 5.3-kb DNA fragment that contained the 5' regulatory region of the rat AChE gene and generated several constructs in which AChE promoter fragments were placed upstream of the reporter gene lacZ and a nuclear localization signal (nls). Using a recently described transient expression assay system in intact skeletal muscle, we show that this AChE promoter fragment directs the synapse-specific expression of the reporter gene. Deletion analysis revealed that a 499-bp fragment located in the first intron of the AChE gene is essential for expression in muscle fibers. Further analysis showed that sequences contained within this intronic fragment were (i) functionally independent of position and orientation and (ii) inactive in hematopoietic cells. Disruption of an N-box motif located within this DNA fragment reduced by more than 80% the expression of the reporter gene in muscle fibers. In contrast, mutation of an adjacent CArG element had no effect on nlsLacZ expression. Taken together, these results indicate that a muscle-specific enhancer is present within the first intron of the AChE gene and that an intronic N-box is essential for the regulation of AChE along skeletal muscle fibers.

GalphaL1 (Galpha14) couples the opioid receptor-like1 receptor to stimulation of phospholipase C

In most tissues and cells the opioid receptor-like (ORL1) receptor regulates effectors primarily through the pertussis toxin (PTX)-sensitive guanine nucleotide-binding regulatory proteins (G proteins) Gi/Go. Many Gi-coupled receptors possess additional capability to interact with one or more PTX-insensitive G proteins. Using the betagamma-induced stimulation of type 2 adenylyl cyclase as a readout, we screened the ability of ORL1 receptor to interact with a panel of PTX-insensitive G proteins. In the presence of PTX, activation of the ORL1 receptor resulted in the stimulation of type 2 adenylyl cyclase only in HEK 293 cells coexpressing the alpha subunit of Gz, G12, G14, or G16, but not in cells coexpressing G11, G13, or Gq. Coupling to both Gz and G16 was expected because close relatives of the ORL1 receptor, the opioid receptors, are known to couple productively to these G proteins. ORL1 receptor coupling to either G12 or G14 has not been demonstrated. As predicted by the type 2 adenylyl cyclase assays, activation of the ORL1 receptor resulted in the formation of inositol phosphates in COS-7 cells transiently cotransfected with Galpha14. The ORL1 receptor-mediated stimulation of phospholipase C was found to be Galpha14 dependent, agonist dose dependent, ligand selective, and PTX insensitive. We conclude that G14 can link the ORL1 receptor to regulation of phopholipase C.

Nerve-derived trophic factors and DNA elements controlling expression of genes encoding synaptic proteins in skeletal muscle fibers

The neuromuscular junction represents an excellent model system for studying various critical issues in neurobiology at the molecular, cellular, and physiological levels. Our understanding of the basic events underlying synpase formation, maintenance, and plasticity has progressed considerably over the last few years primarily because of the numerous studies that have focused on this synapse and used sophisticated recombinant DNA technology. Recent data indicate that myonuclei located in the vicinity of the postsynaptic membrane are in a differential state of transcription compared to nuclei of the extrasynaptic sarcoplasm. Thus, renewal of postsynaptic membrane proteins appears to occur via a mechanism involving the local transcriptional activation of genes encoding these specialized proteins and extracellular cues originating from motoneurons. Such interaction between presynaptic nerve terminals and the postsynaptic sarcoplasm indicates that the entire signal transduction pathway is compartmentalized at the level of the neuromuscular junction. Expression of these genes appears less coregulated than originally anticipated, indicating that maintenance of the postsynaptic membrane requires the contribution of multiple extracellular signals, which ultimately urge target transcription factors to distinct DNA regulatory elements via various second messenger systems.

Increased expression of acetylcholinesterase T and R transcripts during hematopoietic differentiation is accompanied by parallel elevations in the levels of their respective molecular forms

Differentiation of hematopoietic cells is known to be accompanied by profound changes in acetylcholinesterase (AChE) enzyme activity, yet the basic mechanisms underlying this developmental regulation remain unknown. We initiated a series of experiments to examine the molecular mechanisms involved in regulating AChE expression during hematopoiesis. Differentiation of murine erythroleukemia (MEL) cells using dimethyl sulfoxide resulted in a 5- and 10-fold increase in intracellular and secreted AChE enzyme activity, respectively. Interestingly, these increases resulted from a preferential induction of the globular molecular form G1 and a slight increase in G4 instead of an increase in the levels of the G2 membrane-bound form, a molecular form expressed in mature erythrocytes. Concomitantly, expression of the two predominant AChE transcripts (R and T, for read-through and tail, respectively) in MEL cells was induced to a similar extent with differentiation. Nuclear run-on assays performed with nuclei isolated from induced versus uninduced MEL cells revealed that in contrast to the large increases seen in the transcription of the beta-globin gene, the transcriptional activity of the AChE gene remained largely unaffected after differentiation. Determination of the half-lives of the R and T transcripts demonstrated that they both exhibited an increase in stability in induced MEL cells. Taken together, results from these studies indicate that post-transcriptional regulatory mechanisms account for the increased expression of AChE in differentiated hematopoietic cells.

Interaction of lipoprotein lipase with homogeneous lipid emulsions

The central function of lipoprotein lipase (LpL) is to hydrolyze triacylglycerols in chylomicrons and very low density lipoproteins. We have examined the binding of purified milk lipoprotein lipase to homogeneous synthetic lipid emulsions. Emulsions composed of either naturally occurring ester-linked lipids or the non-hydrolyzable ether analogues were prepared by sonication and pressure extrusion, and fractionated by sucrose density gradient centrifugation. Flotation analysis using the analytical ultracentrifuge indicated that the individual fractions were relatively homogeneous with respect to size with flotation coefficients and molecular weights for the separated fractions ranging from 100 to 1100 S and 5.2 x 10(7) to 6.0 x 10(8), respectively. Purified milk lipoprotein lipase bound with high affinity and in a saturable manner to emulsions prepared from the non-hydrolyzable ether-linked lipid analogues of 1-oleoyl, 2-palmitoyl phosphatidylcholine and triolein. At low concentrations of LpL, the enzyme caused aggregation of the emulsion particles by interparticle cross-linking. At higher LpL concentrations, the flotation coefficient of the emulsions decreased significantly with a concomitant increase in particle density. At saturation, the number of LpL monomers bound to lipid particles of radii 67, 75, and 79 nm was 1315, 1449, and 1466, respectively. The results demonstrate close packing of LpL on the lipid surface and are consistent with there being little disruption to the overall structure of the emulsion particle.

Chronic enhancement of neuromuscular activity increases acetylcholinesterase gene expression in skeletal muscle

We determined levels of mRNA encoding acetylcholinesterase (AChE) in muscles of rats subjected to chronic enhancement of neuromuscular activation. After 8 wk of voluntary wheel running, extensor digitorum longus (EDL) muscles displayed a 72% increase in total AChE activity as a result of a selective threefold increase in the G4 content. Soleus muscles, on the other hand, exhibited a 30% decrease in A12 while displaying a small (33%) increase in total AChE activity. These enzymatic adaptations were paralleled by increases in the levels of AChE mRNAs in both EDL (32%; P < 0.03) and soleus (42%; P < 0.02) muscles. In addition, compensatory hypertrophy of the plantaris muscle increased total AChE activity by 75%. This change was reflected by an elevation in all AChE molecular forms with A12 (89%) and A8 (179%) showing the most prominent increases. Similar to exercise-trained muscles, hypertrophied plantaris muscles displayed an increase in AChE transcripts (25%; P < 0.04). These results indicate that increases in neuromuscular activity modulate expression of the AChE gene in vivo and suggest the involvement of pretranslational regulatory mechanisms in the adaptive response of AChE to enhanced neuromuscular activation.

Effect of unesterified cholesterol on the activity of cholesteryl ester transfer protein

Cholesteryl ester transfer protein (CETP) catalyses the transfer of cholesteryl ester from high-density lipoprotein to triacylglycerol-rich lipoproteins and the transfer of triacylglycerols in the reverse direction. The activity of CETP has been studied using a continuous fluorescence assay which measures the excimer fluorescence of cholesteryl 1-pyrene decanoate in a synthetic donor microemulsion as the indicator of cholesteryl ester transfer. Emulsions were composed of cholesteryl oleate and egg phosphatidylcholine and had an average particle size of 14 +/- 1 nm as calculated from the molar volume of the components. The effect of changing the physical state of the emulsion surface was examined by including unesterified cholesterol in the donor and acceptor particles. The rate of CETP-induced transfer of the fluorescent cholesteryl ester between microemulsion particles increased when unesterified cholesterol was present at concentrations up to 17 mol% relative to phospholipid. The presence of cholesterol also changed the exchange kinetics from an apparent single-exponential to a double-exponential phenomenon. Binding of CETP to the emulsion surface was accompanied by an enhancement of fluorescence which was used to measure the binding equilibria. The enhancement of exchange due to the presence of cholesterol did not correlate with any increased binding of CETP to the emulsion surface. The presence of unesterified cholesterol in the donor did not affect the rate of transfer of the fluorescent cholesteryl ester when unlabelled emulsion was replaced by high-density lipoprotein as the acceptor. The studies demonstrate the use of microemulsions of defined size and composition for the study of the mechanism of action of CETP.

Interactions between fatty acids and lipoprotein lipase: specific binding and complex formation

Lipoprotein lipase is the extrahepatic lipase responsible for the hydrolysis of triglycerides in chylomicrons and very low-density lipoproteins. Its enzymic activity and its location on the surface of endothelial cells are affected by the presence of fatty acids, implying that the protein possesses binding sites for that ligand. In this study, we examine the binding of fatty acids to LpL and describe factors that must be considered when the dissociation constant of the acceptor-ligand equilibrium is close to the critical micelle concentration of the fatty acid. The interaction of fatty acids with lipoprotein lipase (LpL) was studied by two methods. A new direct method, based on the LpL-induced increase in the apparent critical micelle concentration of the sodium soap of the fatty acid, indicates the presence of multiple high-affinity binding sites. In the second method, the specific binding of fatty acids to LpL was measured by quantitating the blue shift in the tryptophan fluorescence of LpL that occurs upon binding the ligand. Both methods suggest the existence of 4-6 fatty acid binding sites on LpL with a dissociation constant on the order of 10(-6)-10(-7) M. Further analysis of the blue shift indicates that at higher concentrations of fatty acid, large complexes are formed consisting of 260-310 molecules of fatty acid per LPL monomer. In contrast, no large complexes are formed with fatty acids that form crystals above their solubility limit.

Regulation of transferrin receptor mRNA expression. Distinct regulatory features in erythroid cells

In proliferating non-erythroid cells, the expression of transferrin receptors (TfR) is negatively regulated by the amount of intracellular iron. Fe-dependent regulation of TfR occurs post-transcriptionally and is mediated by iron-responsive elements (IRE) located in the 3' untranslated region of the TfR mRNA. IREs are recognized by a specific cytoplasmic binding protein (IRE-BP) that, in the absence of Fe, binds with high affinity to TfR mRNA, preventing its degradation. While TfR numbers are positively correlated with proliferation in non-erythroid cells, in hemoglobin-synthesizing cells, their numbers increase during differentiation and are, therefore, negatively correlated with proliferation. This suggests a distinct regulation of erythroid TfR expression and evidence, as follows, for this was found in the present study. (a) With nuclear run-on assays, our experiments show increased TfR mRNA transcription following induction of erythroid differentiation of murine erythroleukemia (MEL) with Me2SO. (b) Me2SO treatment of MEL cells does not increase IRE-BP activity which is, however, increased in uninduced MEL cells by Fe chelators. (c) Following induction of MEL cells, there is an increase in the stability of TfR mRNA, whose level is only slightly affected by iron excess. (d) Heme-synthesis inhibitors, such as succinylacetone and isonicotinic acid hydrazide, which inhibit numerous aspects of erythroid differentiation, also inhibit TfR mRNA expression in induced MEL cells. However, heme-synthesis inhibition does not lead to a decrease in TfR mRNA levels in uninduced MEL cells. Thus, these studies indicate that TfR gene expression is regulated differently in hemoglobin synthesizing as compared to uninduced MEL cells.

Development of a novel type of cloning vector for suicide selection of recombinants

Based on the primary structure of the rat corticostatin R4 (antimicrobial defensin RatNP-1), a synthetic gene was designed, synthesized, and inserted into the IPTG-inducible prokaryotic expression vector pFLAG, with an additional 13 codons between the FLAG sequence and the synthetic R4 sequence. This construct, N-p1.2, was further developed by inclusion of multiple cloning sites right after the FLAG sequence, forming a new plasmid pSCV-1. Escherichia coli transformants containing pSCV-1 or N-p1.2 could only be propagated on agar plates in the absence of IPTG due to the detrimental expression of R4 fusion peptide to the growth of bacteria upon IPTG induction. A 214-bp bovine IGF-II cDNA and a 700-bp Ly-6C.2 cDNA fragment were subcloned into pSCV-1 and N-p1.2 respectively. Only the E. coli cells transformed with recombinant plasmids grew on IPTG agar plates. This "suicide" selection against nonrecombinants was further tested in cDNA library construction using pSCV-1. Analysis of plasmid DNA prepared from randomly picked colonies growing on ampicillin agar plates containing IPTG showed all plasmids contained cDNA inserts. The lambda Hind III fragments were used for comparing the cloning efficiency of pSCV-1 to pBluescript. Four of the 60 (6.6%) analyzed white colonies transformed with pBluescript were false positives. All of the analyzed pSCV-1-transformed colonies growing on IPTG plates contained recombinant forms of plasmid. The percentage recovery of each ligatable lambda Hind III fragment was similar in both pBluescript and pSCV-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of ferrochelatase mRNA in erythroid and non-erythroid cells

Ferrochelatase, which catalyses the last step in haem biosynthesis, i.e. the insertion of Fe(II) into protophorphyrin IX, is present in all cells, but is particularly abundant in erythroid cells during haemoglobinization. Using mouse ferrochelatase cDNA as a probe two ferrochelatase transcripts, having lengths of 2.9 kb and 2.2 kb, were found in extracts of mouse liver, kidney, brain, muscle and spleen, the 2.9 kb transcript being more abundant in the non-erythroid tissues and the 2.2 kb transcript more predominant in spleen. In mouse erythroleukemia cells the 2.9 kb ferrochelatase transcript is also more abundant; however, following induction of erythroid differentiation by dimethyl sulphoxide there is a preferential increase in the 2.2 kb transcript, which eventually predominates. With mouse reticulocytes, the purest immature erythroid cell population available, over 90% of the total ferrochelatase mRNA is present as the 2.2 kb transcript. Since there is probably only one mouse ferrochelatase gene, the occurrence of two ferrochelatase transcripts could arise from the use of two putative polyadenylation signals in the 3' region of ferrochelatase DNA. This possibility was explored by using a 389 bp DNA fragment produced by PCR with synthetic oligoprimers having sequence similarity with a region between the polyadenylation sites. This fragment hybridized only to the 2.9 kb ferrochelatase transcript, indicating that the two transcripts differ at their 3' ends and suggesting that the 2.2 kb transcript results from the utilization of the upstream polyadenylation signal. The preferential utilization of the upstream polyadenylation signal may be an erythroid-specific characteristic of ferrochelatase gene expression.

Transferrin-receptor-independent but iron-dependent proliferation of variant Chinese hamster ovary cells

The purpose of this study is to clarify the role of iron, transferrin, an iron-binding protein in vertebrate plasma, and transferrin receptors in cell proliferation. Transferrin, which is indispensable for most cells growing in tissue culture, is frequently referred to as a "growth factor". Proliferating cells express high numbers of transferrin receptors, and the binding of transferrin to their receptors that is needed for cells to initiate and maintain their DNA synthesis is sometimes regarded as analogous to other growth factor-receptor interactions. Although numerous previous experiments strongly indicate that the only function of transferrin in supporting cell proliferation is supplying cells with iron, they did not completely rule out some direct or signaling role transferrin receptors could play in cell proliferation. To address this issue, we exploited transferrin-receptor-deficient mutant Chinese hamster ovary (CHO) cells (McGraw, T. E., Greenfield, L., and Maxfield, F. R., 1987, J. Cell. Biol. 105, 207-214) in which various aspects of iron and transferrin metabolism in relation to their capacity to proliferate were investigated. Variant cells neither specifically bind transferrin nor do their extracts contain any detectable functional transferrin receptors, yet they proliferate and synthesize DNA with rates comparable to those observed with parent CHO cells. Desferrioxamine, an iron chelating agent, inhibits growth and DNA synthesis of both variant and control CHO cells. This inhibition can be fully alleviated, in both cell types, by ferric pyridoxal isonicotinoyl hydrazone, which can supply cells with a utilizable form of iron by a pathway not requiring transferrin and their receptors. Studies of 59Fe uptake and 125I-transferrin binding revealed that parent cells can take up iron by at least three mechanisms: from transferrin by receptor-dependent and -independent (nonspecific, nonsaturable, not requiring acidification) pathways and from inorganic iron salts (initially present in the medium as FeSO4). Although variant CHO cells are unable to acquire transferrin iron via the receptor pathway, two remaining mechanisms provide these cells with sufficient amounts of iron for DNA synthesis and cell proliferation. In conclusion, although transferrin receptors are dispensable in terms of their absolute requirement for proliferating cells, a supply of iron is still needed for their DNA synthesis. Transferrin-receptor-deficient CHO cells may be a useful model for investigating receptor-independent iron uptake from transferrin and nontransferrin iron sources.

omega-6 and omega-3 fatty acids: monolayer packing and effects on bilayer permeability and cholesterol exchange

It has been suggested that the polyunsaturated omega-3 fatty acid, docosahexaenoic acid (DHA), can adopt unique closely packed arrays in lipid bilayers (Glomset and Applegate. (1986) J. Lipid Res. 27, 658-680). These conformations are predicted on the basis of molecular dynamics calculations and are in contrast to the expanded conformations characteristic of omega-6 unsaturated fatty acids. It has also been suggested that close packing of omega-3 acyl chains could have a substantial affect on the physical properties of lipid bilayers (e.g. permeability). We report here some experimental tests of these predictions. Surface pressure-area experiments have been carried out on DHA and its mixtures with stearic and oleic acids. At low surface pressures DHA is more expanded than oleic acid. Extrapolation to the high surface pressures characteristic of lipid bilayers indicates that the area per molecule of DHA is only marginally less than that for oleic acid. Thus there is no compelling evidence to suggest that the average area per molecule of the omega-3 fatty acid is substantially different from the omega-6 fatty acid at high surface pressures. Experiments also show that the permeability of bilayers to glucose and the rates of dissociation of pyrenyl cholesterol from bilayers were similar for bilayers containing DHA compared to bilayers containing oleic acid or linoleic acid.

Spectrofluorometric determination of lipase activity

A fluorescent triglyceride, 1(3)-pyrenylbutanoyl-2,3(1,2)-dipalmitoyl-sn-glycerol, was synthesised, characterised by NMR and mass spectrometry, incorporated into a lipid emulsion and used as a fluorescent substrate for pancreatic lipase. It is shown that the product of the reaction, pyrene butyric acid, diffuses into the aqueous phase resulting in a decrease in the excimer fluorescence of the pyrene fluorophore in the emulsion and an increase in its monomer fluorescence. The phenomenon can be used to assay the enzyme thereby cirumventing the need to extract the fatty acid product.

Perturbation of intracellular pH by DIDS on endocytosis of transferrin and iron uptake in rabbit reticulocytes

DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) inhibited transferrin and iron uptake by rabbit reticulocytes in a dose-dependent manner. Measurement of intracellular pH shows that DIDS neutralized the pH in the intracellular vesicles and at the same time, rendered the cytoplasmic pH more acidic. The latter may be the result of a perturbance in the acid-extruding mechanism(s) by DIDS, a known anion exchange blocker. Examination of the single-cycle endocytosis of transferrin with pulse-chased technique suggests that DIDS retarded transferrin internalization, iron unloading and transferrin receptor recycling in the cells.

The membrane effect of 1-anilino-8-naphthalene sulfonate on transferrin and iron uptake by rabbit reticulocytes

Studies on the effect of 1-anilino-8-naphthalene sulfonate on uptake of transferrin and iron by rabbit reticulocytes show that the inhibitory action of ANS is localized at the membrane level. The intravesicular pH and cellular ATP level were not affected by this anionic probe. ANS shifted the transition temperature and reduced the enthalpy changes of iron uptake by rabbit reticulocytes. These suggested that the drug reduced the membrane fluidity. Hence, ANS disturbed the physicochemical environment of the receptor for transferrin resulting in the perturbation of receptor-mediated endocytosis.

Effects of spermine on transferrin and iron uptake by reticulocytes: II. Changes in intravesicular pH

An increase in extracellular spermine concentration brought about a progressive rise in intralysosomal pH in rabbit reticulocytes. Since intracellular release of iron from transferrin is believed to involve the protonation of the iron-transferrin complex, the rise in intralysomal pH could account for the inhibitory effect of spermine on iron uptake. The inhibition could be reversed if spermine was removed by washing. As a result of spermine treatment, more acid-labile N-terminal monoferric transferrin and less apotransferrin were released from the cell. These results are consistant with the protonation theory of iron release.

Effects of spermine on transferrin and iron uptake by reticulocytes: I. Action on the endocytic uptake of transferrin

Iron uptake by rabbit reticulocytes was inhibited by spermine in a concentration-dependent manner. Examination of the single-cycle endocytosis of 125I-transferrin showed that a graded reduction in the rate of exocytosis of transferrin was related to increasing extracellular spermine concentrations. This reduction could affect the recycling of transferrin receptors and resulted in the loss of membrane binding sites in spermine-treated cells. As large vacuoles were observed in cells treated with spermine, the endotubular function of these cells was probably affected. Spermine also enhanced the binding affinity of transferrin to membrane receptors. The mechanism for this enhancement was not clear.

Anterior segment configuration correlated with Shaffer's grading of anterior chamber angle

The central corneal thickness, peripheral corneal thickness, central anterior chamber depth, and peripheral anterior chamber depth were measured from 110 phakic eyes using attachments 1 and 2 to the slitlamp (Haag-Streit). The Shaffer grading system was used for the width of the anterior chamber angle. The results showed that both the average central anterior chamber depth and peripheral anterior chamber depth increased in a linear manner with the Shaffer grading system of the width of the anterior chamber angle. In addition, our "scattergram" showed that each Shaffer grading of the angle width could almost be uniquely determined by the combination of central and peripheral anterior chamber depths. However, the peripheral anterior chamber depth is the best single factor in predicting the Shaffer grading of the width of the anterior chamber angle.

Spatial organizations of catfish retinal neurons. II. Circular stimulus

1. Temporal dynamics of receptive-field components were identified by use of circular stimuli whose diameter was modulated in white-noise fashion. 2. A thin ring of light evoked a complex response from the horizontal-cell soma but not from its axon. 3. All bipolar cells had a biphasic receptive field whose incremental sensitivities were comparable for the field's center and surround. 4. Type-N cells had a biphasic field whose two components were segregated both in time and space. 5. Type-C cells showed nonlinearities, which did not depend on the types of light inputs and which were intrinsic to the cell. 6. Ganglion cells could be classified roughly into two classes: small- and large-field cells. Their main nonlinearity was rectification. 7. Our studies on the catfish retna have shown that the distal cells are essentially linear in time and space and can be identified functionally by any type of input. The proximal cells, however, have a complex functional repertoire whose identification poses considerable difficulty.

Adaptation in catfish retina

1. We define absolute sensitivity as (voltage/illuminance) and incremental sensitivity as the peak-to-peak amplitude of the first-order (Wiener) kernels. 2. Incremental sensitivity of the horizontal cells is the local slopes of the Michaelis-Menten equation and that of more proximal neurons is the Fechner slope. In a log-log plot, the former has a slope of -2, whereas the latter a slope of -1, as predicted by Williams and Gale (39). 3. During a moderate to strong steady illumination, absolute sensitivity decreases but incremental sensitivity increases. The reverse occurs during dark adaptation. 4. The presence of a steady illumination did not prevent signal transmission from horizontal to ganglion cells. 5. From these results we conclude that: adaptation in the catfish retina includes two components: a) a lateral shift of the voltage-intensity curve along the intensity axis, and b) changes in the time course of light-evoked response. We argue that the latter phenomenon is related to the presumed horizontal cell-to-receptor cell negative feedback.