Circulating tumor DNA as a potential marker of adjuvant chemotherapy benefit following surgery for localized pancreatic cancer.

BACKGROUND: In early-stage pancreatic cancer, there are currently no biomarkers to guide selection of therapeutic options. This prospective biomarker trial evaluated the feasibility and potential clinical utility of circulating tumor DNA (ctDNA) analysis to inform adjuvant therapy decision making. MATERIALS AND METHODS: Patients considered by the multidisciplinary team to have resectable pancreatic adenocarcinoma were enrolled. Pre- and post-operative samples for ctDNA analysis were collected. PCR-based-SafeSeqS assays were used to identify mutations at codon 12, 13 and 61 of KRAS in the primary pancreatic tumor and to detect ctDNA. Results of ctDNA analysis were correlated with CA19-9, recurrence-free and overall survival (OS). Patient management was per standard of care, blinded to ctDNA data. RESULTS: Of 112 patients consented pre-operatively, 81 (72%) underwent resection. KRAS mutations were identified in 91% (38/42) of available tumor samples. Of available plasma samples (N = 42), KRAS mutated ctDNA was detected in 62% (23/37) pre-operative and 37% (13/35) post-operative cases. At a median follow-up of 38.4 months, ctDNA detection in the pre-operative setting was associated with inferior recurrence-free survival (RFS) [hazard ratio (HR) 4.1; P = 0.002)] and OS (HR 4.1; P = 0.015). Detectable ctDNA following curative intent resection was associated with inferior RFS (HR 5.4; P < 0.0001) and OS (HR 4.0; P = 0.003). Recurrence occurred in 13/13 (100%) patients with detectable ctDNA post-operatively, including in seven that received gemcitabine-based adjuvant chemotherapy. CONCLUSION: ctDNA studies in localized pancreatic cancer are challenging, with a substantial number of patients not able to undergo resection, not having sufficient tumor tissue for analysis or not completing per protocol sample collection. ctDNA analysis, pre- and/or post-surgery, is a promising prognostic marker. Studies of ctDNA guided therapy are justified, including of treatment intensification strategies for patients with detectable ctDNA post-operatively who appear at very high risk of recurrence despite gemcitabine-based adjuvant therapy.

The protective role of Toll-like receptor 3 and type-I interferons in the pathophysiology of vein graft disease.

BACKGROUND: Venous grafts are commonly used as conduits to bypass occluded arteries. Unfortunately, patency rates are limited by vein graft disease (VGD). Toll like receptors (TLRs) can be activated in vein grafts by endogenous ligands. This study aims to investigate the role of TLR3 in VGD. METHODS: Vein graft surgery was performed by donor caval vein interpositioning in the carotid artery of recipient Tlr2-/-, Tlr3-/-, Tlr4-/- and control mice. Vein grafts were harvested 7, 14 and 28d after surgery to perform immunohistochemical analysis. Expression of TLR-responsive genes in vein grafts was analysed using a RT2-profiler PCR Array. mRNA expression of type-I IFN inducible genes was measured with qPCR in bone marrow-derived macrophages (BMM). RESULTS: TLR2, TLR3 and TLR4 were observed on vein graft endothelial cells, smooth muscle cells and macrophages. Tlr3-/- vein grafts demonstrated no differences in vessel wall thickening after 7d, but after 14d a 2.0-fold increase (p = 0.02) and 28d a 1.8-fold increase (p = 0.009) compared to control vein grafts was observed, with an increased number of macrophages (p = 0.002) in the vein graft. Vessel wall thickening in Tlr4-/- decreased 0.6-fold (p = 0.04) and showed no differences in Tlr2-/- compared to control vein grafts. RT2-profiler array revealed a down-regulation of type-I IFN inducible genes in Tlr3-/- vein grafts. PolyI:C stimulated BMM of Tlr3-/- mice showed a reduction of Ifit1 (p = 0.003) and Mx1 (p < 0.0001) mRNA compared to control. CONCLUSIONS: We here demonstrate that TLR3 can play a protective role in VGD development, possibly regulated via type-I IFNs and a reduced inflammatory response.

The Influence of End-of-Life Care on Organ Donor Potential.

Many patients with acute devastating brain injury die outside intensive care units and could go unrecognized as potential organ donors. We conducted a prospective observational study in seven hospitals in the Netherlands to define the number of unrecognized potential organ donors outside intensive care units, and to identify the effect that end-of-life care has on organ donor potential. Records of all patients who died between January 2013 and March 2014 were reviewed. Patients were included if they died within 72 h after hospital admission outside the intensive care unit due to devastating brain injury, and fulfilled the criteria for organ donation. Physicians of included patients were interviewed using a standardized questionnaire regarding logistics and medical decisions related to end-of-life care. Of the 5170 patients screened, we found 72 additional potential organ donors outside intensive care units. Initiation of end-of-life care in acute settings and lack of knowledge and experience in organ donation practices outside intensive care units can result in under-recognition of potential donors equivalent to 11-34% of the total pool of organ donors. Collaboration with the intensive care unit and adjusting the end-of-life path in these patients is required to increase the likelihood of organ donation.

A protective role of IRF3 and IRF7 signalling downstream TLRs in the development of vein graft disease via type I interferons.

BACKGROUND: Toll like receptors (TLR) play an important role in vein graft disease (VGD). Interferon regulatory factors (IRF) 3 and 7 are the transcriptional regulators of type I interferons (IFN) and type I IFN responsive genes and are downstream factors of TLRs. Relatively little is known with regard to the interplay of IRFs and TLRs in VGD development. The aim of this study was to investigate the role of IRF3 and IRF7 signaling downstream TLRs and the effect of IRF3 and IRF7 in VGD. METHODS AND RESULTS: In vitro activation of TLR3 induced IRF3 and IRF7 dependent IFNß expression in bone marrow macrophages and vascular smooth muscle cells. Activation of TLR4 showed to regulate pro-inflammatory cytokines via IRF3. Vein graft surgery was performed in Irf3-/- , Irf7-/- and control mice. After 14 days Irf3-/- vein grafts had an increased vessel wall thickness compared to both control (P = 0.01) and Irf7-/- (P = 0.02) vein grafts. After 28 days, vessel wall thickness increased in Irf3-/- (P = 0.0003) and Irf7-/- (P = 0.04) compared to control vein grafts and also increased in Irf7-/- compared to Irf3-/- vein grafts (P = 0.02). Immunohistochemical analysis showed a significant higher influx of macrophages after 14 days in Irf3-/- vein grafts and after 28 days in Irf7-/- vein grafts compared to control vein grafts. CONCLUSIONS: The present study is the first to describe a protective role of both IRF3 and IRF7 in VGD. IRFs regulate VGD downstream TLRs since Irf3-/- and Irf7-/- vein grafts show increased vessel wall thickening after respectively 14 and 28 days after surgery.

Physiologic Changes in the Heart Following Cessation of Mechanical Ventilation in a Porcine Model of Donation After Circulatory Death: Implications for Cardiac Transplantation.

Hearts donated following circulatory death (DCD) may represent an additional source of organs for transplantation; however, the impact of donor extubation on the DCD heart has not been well characterized. We sought to describe the physiologic changes that occur following withdrawal of life-sustaining therapy (WLST) in a porcine model of DCD. Physiologic changes were monitored continuously for 20 min following WLST. Ventricular pressure, volume, and function were recorded using a conductance catheter placed into the right (N = 8) and left (N = 8) ventricles, and using magnetic resonance imaging (MRI, N = 3). Hypoxic pulmonary vasoconstriction occurred following WLST, and was associated with distension of the right ventricle (RV) and reduced cardiac output. A 120-fold increase in epinephrine was subsequently observed that produced a transient hyperdynamic phase; however, progressive RV distension developed during this time. Circulatory arrest occurred 7.6±0.3 min following WLST, at which time MRI demonstrated an 18±7% increase in RV volume and a 12±9% decrease in left ventricular volume compared to baseline. We conclude that hypoxic pulmonary vasoconstriction and a profound catecholamine surge occur following WLST that result in distension of the RV. These changes have important implications on the resuscitation, preservation, and evaluation of DCD hearts prior to transplantation.

Short-term health effects in the general population following a major train accident with acrylonitrile in Belgium.

BACKGROUND: Following a train derailment, several tons of acrylonitrile (ACN) exploded, inflamed and part of the ACN ended up in the sewage system of the village of Wetteren. More than 2000 residents living in the close vicinity of the accident and along the sewage system were evacuated. A human biomonitoring study of the adduct N-2-cyanoethylvaline (CEV) was carried out days 14-21 after the accident. OBJECTIVES: (1) To describe the short-term health effects that were reported by the evacuated residents following the train accident, and (2) to explore the association between the CEV concentrations, extrapolated at the time of the accident, and the self-reported short-term health effects. METHODS: Short-term health effects were reported in a questionnaire (n=191). An omnibus test of independence was used to investigate the association between the CEV concentrations and the symptoms. Dose-response relationships were quantified by Generalized Additive Models (GAMs). RESULTS: The most frequently reported symptoms were local symptoms of irritation. In non-smokers, dose-dependency was observed between the CEV levels and the self-reporting of irritation (p=0.007) and nausea (p=0.007). Almost all non-smokers with CEV concentrations above 100pmol/g globin reported irritation symptoms. Both absence and presence of symptoms was reported by non-smokers with CEV concentrations below the reference value and up to 10 times the reference value. Residents who visited the emergency services reported more symptoms. This trend was seen for the whole range of CEV concentrations, and thus independently of the dose. DISCUSSION AND CONCLUSION: The present study is one of the first to relate exposure levels to a chemical released during a chemical incident to short-term (self-reported) health effects. A dose-response relation was observed between the CEV concentrations and the reporting of short-term health effects in the non-smokers. Overall, the value of self-reported symptoms to assess exposure showed to be limited. The results of this study confirm that a critical view should be taken when considering self-reported health complaints and that ideally biomarkers are monitored to allow an objective assessment of exposure.

A Novel von Hippel Lindau Gene Intronic Variant and Its Reclassification from VUS to Pathogenic: the Impact on a Large Family.

We present a case where a variant of uncertain significance in the von Hippel Lindau syndrome gene (VHL) was identified in a proband with haemangioblastoma, and in a second degree relative with phaeochromocytoma. Initial uncertainty due to the unclear nature of the variant created psychosocial challenges for this family, in which four other genetic conditions were also present. Subsequent RNA studies confirmed this as a novel pathogenic mutation affecting splicing of exon 2. A third relative has since been diagnosed with haemangioblastoma. We suggest that this mutation possibly has reduced penetrance as there was no history of haemangioblastoma, renal tumours (apart from small cysts) or other VHL tumours among five mutation positive and seven untested adult relatives at 50 % risk of the VHL mutation (average age 46 years, range 18-70 years). This case presents a novel VHL splicing mutation and highlights the psychosocial and medical value of additional laboratory studies on uncertain variants for individuals, their families and for the health professionals providing advice and counseling.

[Recovery from locked-in syndrome: rule rather than exception]. / Herstel na locked-insyndroom.

The prognosis for locked-in syndrome after acquired brainstem injury is unfavourable. However, partial recovery of motor function occurs in many patients and benefits from intensive rehabilitation. Here we evaluate two patient cases and results of a questionnaire among medical doctors specialised in rehabilitation. We define bottlenecks in the treatment of acute locked-in syndrome in the ICU. Locked-in patients have a years-long life expectancy once they have survived the acute phase. There is no validated prognostic instrument to predict recovery, but even small neurological recovery can have large functional benefits. Recovery may take place over an extended period of time, up to years after onset. To unlock the potential to recover we recommend to start with early rehabilitation while the patient is still in the ICU on life sustaining treatment This may set the patient off along the road from locked-in to unlocked.

In-depth assessment of health-related quality of life after in-hospital cardiac arrest.

INTRODUCTION: Evidence on physical and psychological well-being of in-hospital cardiac arrest (IHCA) survivors is scarce. The aim of this study is to describe long-term health-related quality of life (HRQoL), functional independence and psychological distress 3 and 12 months post-IHCA. METHODS: A multicenter prospective cohort study in 25 hospitals between January 2017 - May 2018. Adult IHCA survivors were included. HRQoL (EQ-5D-5L, SF-12), psychological distress (HADS, CSI) and functional independence (mRS) were assessed at 3 and 12 months post-IHCA. RESULTS: At 3-month follow-up 136 of 212 survivors responded to the questionnaire and at 12 months 110 of 198 responded. The median (IQR) EQ-utility Index score was 0.77 (0.65-0.87) at 3 months and 0.81 (0.70-0.91) at 12 months. At 3 months, patients reported a median SF-12 (IQR) physical component scale (PCS) of 38.9 (32.8-46.5) and mental component scale (MCS) of 43.5 (34.0-39.7) and at 12 months a PCS of 43.1 (34.6-52.3) and MCS 46.9 (38.5-54.5). DISCUSSION: Using various tools most IHCA survivors report an acceptable HRQoL and a substantial part experiences lower HRQoL compared to population norms. Our data suggest that younger (male) patients and those with poor functional status prior to admission are at highest risk of impaired HRQoL.

Caveolae, DIGs, and the dynamics of sphingolipid-cholesterol microdomains.

There is accumulating evidence that lateral assemblies (rafts) of sphingolipids and cholesterol form platforms that serve to support numerous cellular events in membrane traffic and signal transduction. Raft membrane microdomains are thought to function by preferentially associating with specific proteins while excluding others. The basic forces driving raft formation are lipid interactions which are, per se, weak and transient. Sphingolipid rafts should therefore be considered to be dynamic structures in which cholesterol plays an important role as a linker. Caveolins influence these dynamics by forming stabilized raft domains in intracellular membranes as well as at the plasma membrane. Recent data suggest that clustering of raft components could regulate raft dynamics and therefore represents an important feature in the function of these membrane microdomains.

Multicolour imaging of post-Golgi sorting and trafficking in live cells.

The biogenesis and maintenance of asymmetry is crucial to many cellular functions including absorption and secretion, signalling, development and morphogenesis. Here we have directly visualized the segregation and trafficking of apical (glycosyl phosphatidyl inositol-anchored) and basolateral (vesicular stomatitis virus glycoprotein) cargo in living cells using multicolour imaging of green fluorescent protein variants. Apical and basolateral cargo segregate progressively into large domains in Golgi/trans-Golgi network structures, exclude resident proteins, and exit in separate transport containers. These remain distinct and do not merge with endocytic structures suggesting that lateral segregation in the trans-Golgi network is the primary sorting event. Fusion with the plasma membrane was detected by total internal reflection microscopy and reveals differences between apical and basolateral carriers as well as new 'hot spots' for exocytosis.

A cross-sectional investigation of communication in Do-Not-Resuscitate orders in Dutch hospitals.

BACKGROUND: The decision to attempt or refrain from resuscitation is preferably based on prognostic factors for outcome and subsequently communicated with patients. Both patients and physicians consider good communication important, however little is known about patient involvement in and understanding of cardiopulmonary resuscitation (CPR) directives. AIM: To determine the prevalence of Do Not Resuscitate (DNR)-orders, to describe recollection of CPR-directive conversations and factors associated with patient recollection and understanding. METHODS: This was a two-week nationwide multicentre cross-sectional observational study using a study-specific survey. The study population consisted of patients admitted to non-monitored wards in 13 hospitals. Data were collected from the electronic medical record (EMR) concerning CPR-directive, comorbidity and at-home medication. Patients reported their perception and expectations about CPR-counselling through a questionnaire. RESULTS: A total of 1136 patients completed the questionnaire. Patients' CPR-directives were documented in the EMR as follows: 63.7% full code, 27.5% DNR and in 8.8% no directive was documented. DNR was most often documented for patients >80 years (66.4%) and in patients using >10 medications (45.3%). Overall, 55.8% of patients recalled having had a conversation about their CPR-directive and 48.1% patients reported the same CPR-directive as the EMR. Most patients had a good experience with the CPR-directive conversation in general (66.1%), as well as its timing (84%) and location (94%) specifically. CONCLUSIONS: The average DNR-prevalence is 27.5%. Correct understanding of their CPR-directive is lowest in patients aged ≥80 years and multimorbid patients. CPR-directive counselling should focus more on patient involvement and their correct understanding.

Attitudes of Dutch intensive care unit clinicians towards oxygen therapy.

BACKGROUND: Over the last decade, there has been an increasing awareness for the potential harm of the administration of too much oxygen. We aimed to describe self-reported attitudes towards oxygen therapy by clinicians from a large representative sample of intensive care units (ICUs) in the Netherlands. METHODS: In April 2019, 36 ICUs in the Netherlands were approached and asked to send out a questionnaire (59 questions) to their nursing and medical staff (ICU clinicians) eliciting self-reported behaviour and attitudes towards oxygen therapy in general and in specific ICU case scenarios. RESULTS: In total, 1361 ICU clinicians (71% nurses, 24% physicians) from 28 ICUs returned the questionnaire. Of responding ICU clinicians, 64% considered oxygen-induced lung injury to be a major concern. The majority of respondents considered a partial pressure of oxygen (PaO2) of 6-10 kPa (45-75 mmHg) and an arterial saturation (SaO2) of 85-90% as acceptable for 15 minutes, and a PaO2 7-10 kPa (53-75 mmHg) and SaO2 90-95% as acceptable for 24-48 hours in an acute respiratory distress syndrome (ARDS) patient. In most case scenarios, respondents reported not to change the fraction of inspired oxygen (FiO2) if SaO2 was 90-95% or PaO2 was 12 kPa (90 mmHg). CONCLUSION: A representative sample of ICU clinicians from the Netherlands were concerned about oxygen-induced lung injury, and reported that they preferred PaO2 and SaO2 targets in the lower physiological range and would adjust ventilation settings accordingly.

Jamming the endosomal system: lipid rafts and lysosomal storage diseases.

Some lysosomal storage diseases result from the accumulation of lipids in degradative compartments of the endocytic pathway. Particularly striking is the example of the Niemann-Pick (NP) syndrome. NP syndromes types A and B are characterized by the accumulation of sphingomyelin, whereas cholesterol typically accumulates in NP type C. These two different lipids, sphingomyelin and cholesterol, are normal constituents of specific lipid microdomains called rafts. Because accumulation of raft lipids is observed not only in NP diseases but also in many other lipidoses, we forward the hypothesis that lysosomal storage diseases can be caused by the accumulation of lipid rafts in late endosomes/lysosomes.

Transferrin receptor polarity and recycling accuracy in "tight" and "leaky" strains of Madin-Darby canine kidney cells.

We have characterized the polarity of the transferrin receptor in the epithelial Madin-Darby canine kidney (MDCK) cell line. The receptor is present in approximately 165,000 copies per cell, migrates as a diffuse band upon SDS gel electrophoresis with Mr 90,000, displays a dissociation constant for diferritransferrin at neutral pH of approximately 2 nM, and is active in essentially all of the cells of the population. Transferrin-mediated 55Fe uptake was used to measure the polarity of active transferrin receptors in filter-grown MDCK cells. The ratio of basolateral to apical receptors was approximately 800:1 for the high resistance strain I MDCK cells (typically greater than 2,000 ohm X cm2) and approximately 300:1 for the lower resistance strain II cells (less than 350 ohm X cm2). In combination with morphometric data this shows that a difference in resistance between these two strains is not reflected in a significant difference in cell surface polarity. We used the recycling of transferrin receptor in filter-grown MDCK cells to evaluate the accuracy of the sorting of a basolateral protein during endocytosis. Monitoring the amount of apically released 125I-labeled transferrin after application of 55Fe- and 125I-labeled transferrin to the basolateral surface provided a sensitive assay of the accuracy of sorting during recycling of the receptor from endosomes to the plasma membrane. The accuracy of transferrin receptor sorting (greater than 99.88%) during a single cycle of transit between the endosome and the plasma membrane is sufficient to maintain the high level of polarity of the cell.

A functional assay for proteins involved in establishing an epithelial occluding barrier: identification of a uvomorulin-like polypeptide.

A functional assay has been developed to identify cell surface proteins involved in the formation of epithelial tight junctions. Transepithelial electrical resistance was used to measure the presence of intact tight junctions in monolayers of Madin-Darby canine kidney (MDCK) cells cultured on nitrocellulose filters. The strain I MDCK cells used have a transmonolayer resistance greater than 2,000 ohm . cm2. When the monolayers were incubated at 37 degrees C without Ca2+, the intercellular junctions opened and the transmonolayer resistance dropped to the value of a bare filter, i.e., less than 40 ohm . cm2. When Ca2+ was restored, the cell junctions resealed and the resistance recovered rapidly. Polyclonal antibodies raised against intact MDCK cells inhibited the Ca2+-dependent recovery of electrical resistance when applied to monolayers that had been opened by Ca2+ removal. Cross-linking of cell surface molecules was not required because monovalent Fab' fragments also inhibited. In contrast, a variety of other antibodies that recognize specific proteins on the MDCK cell surface failed to inhibit the recovery of resistance. Monoclonal antibodies have been raised and screened for their ability to inhibit resistance recovery. One such monoclonal antibody has been obtained that stained the lateral surface of MDCK cells. This antibody, rr1, recognized a 118-kD polypeptide in MDCK cell extracts and an 81-kD fragment released from the cell surface by trypsinization in the presence of Ca2+. Sequential immunoprecipitation with antibody rr1 and a monoclonal antibody to uvomorulin showed that this polypeptide is related to uvomorulin. The role of uvomorulin-like and liver cell adhesion molecule (L-CAM)-like polypeptides in the establishment of the epithelial occluding barrier is discussed.

An efficient method for introducing defined lipids into the plasma membrane of mammalian cells.

An efficient method has been devised to introduce lipid molecules into the plasma membrane of mammalian cells. This method has been applied to fuse lipid vesicles with the apical plasma membrane of Madin-Darby canine kidney cells. The cells were infected with fowl plague or influenza N virus. 4 h after infection, the hemagglutinin (HA) spike glycoprotein of the virus was present in the apical plasma membrane of the cells. Lipid vesicles containing egg phosphatidylcholine, cholesterol, and an HA receptor (ganglioside) were then bound to the cells at 0 degrees C. More than 85% of the vesicles were released by external neuraminidase at 0 degrees C or by simply warming the cells to 37 degrees C for 10 s, probably because of the action of the viral neuraminidase at the cell surface. However, when the cells were warmed to 37 degrees C in a pH 5.3 medium for 30 s, 50% of the bound vesicles could no longer be released by external neuraminidase. This only occurred when the HA protein had been cleaved into its HA1 and HA2 subunits. When we used influenza N virus, whose HA is not cleaved in Madin-Darby canine kidney cells, cleavage with external trypsin was required. The fact that the HA protein has fusogenic properties at low pH only in its cleaved form suggests that fusion of the vesicles with the plasma membrane had taken place. Further confirmation for fusion was obtained using an assay based on the decrease of energy transfer between two fluorescent phospholipids in a vesicle upon fusion of the vesicle with the plasma membrane (Struck, D. K., D. Hoekstra, and R. E. Pagano. 1981. Biochemistry, 20:4093-4099).

Transepithelial transport of a viral membrane glycoprotein implanted into the apical plasma membrane of Madin-Darby canine kidney cells. II. Immunological quantitation.

The envelope of vesicular stomatitis virus was fused with the apical plasma membrane of Madin-Darby canine kidney cells by low pH treatment. The fate of the implanted G protein was then followed using a protein A-binding assay, which was designed to quantitate the amount of G protein in the apical and the basolateral membranes. The implanted G protein was rapidly internalized at 31 degrees C, whereas at 10 degrees C no uptake was observed. Already after 15 min at 31 degrees C, a fraction of the G protein could be detected at the basolateral membrane. After 60 min 25-48% of the G protein was basolateral as measured by the protein A-binding assay. At the same time, 25-33% of the implanted G protein was detected at the apical membrane. Internalization of G protein was not affected by 20 mM ammonium chloride or by 10 microM monensin. However, the endocytosed G protein accumulated in intracellular vacuoles and redistribution back to the plasma membrane was inhibited. We conclude that the implanted G protein was rapidly internalized from the apical surface of Madin-Darby canine kidney cells and a major fraction was routed to the basolateral domain.

Cholesterol is required for surface transport of influenza virus hemagglutinin.

Transport from the TGN to the basolateral surface involves a rab/N-ethylmaleimide-sensitive fusion protein (NSF)/soluble NSF attachment protein (SNAP)/SNAP receptor (SNARE) mechanism. Apical transport instead is thought to be mediated by detergent-insoluble sphingolipid-cholesterol rafts. By reducing the cholesterol level of living cells by 60-70% with lovastatin and methyl-beta-cyclodextrin, we show that the TGN-to-surface transport of the apical marker protein influenza virus hemagglutinin was slowed down, whereas the transport of the basolateral marker vesicular stomatitis virus glycoprotein as well as the ER-to-Golgi transport of both membrane proteins was not affected. Reduction of transport of hemagglutinin was accompanied by increased solubility in the detergent Triton X-100 and by significant missorting of hemagglutinin to the basolateral membrane. In addition, depletion of cellular cholesterol by lovastatin and methyl-beta-cyclodextrin led to missorting of the apical secretory glycoprotein gp-80, suggesting that gp-80 uses a raft-dependent mechanism for apical sorting. Our data provide for the first time direct evidence for the functional significance of cholesterol in the sorting of apical membrane proteins as well as of apically secreted glycoproteins.

Sorting of an apical plasma membrane glycoprotein occurs before it reaches the cell surface in cultured epithelial cells.

In Madin-Darby canine kidney (MDCK) cells (a polarized epithelial cell line) infected with influenza virus, the hemagglutinin behaves as an apical plasma membrane glycoprotein. To determine biochemically the domain on the plasma membrane, apical or basolateral, where newly synthesized hemagglutinin first appears, cells were cultured on Millipore filters to make both cell surface domains independently accessible. Hemagglutinin in virus-infected cells was pulse-labeled, chased, and detected on the plasma membrane with a sensitive trypsin assay. Under all conditions tested, newly made hemagglutinin appeared simultaneously on both domains, with the bulk found in the apical membrane. When trypsin was continuously present on the basolateral surface during the chase, little hemagglutinin was cleaved relative to the amount transported apically. In addition, specific antibodies against the hemagglutinin placed basolaterally had no effect on transport to the apical domain. These observations suggested that most newly synthesized hemagglutinin does not transiently appear on the basolateral surface but rather is delivered directly to the apical surface in amounts that account for its final polarized distribution.