Ten-year reduction in thoracic injury-related mortality among Israel Defense Forces soldiers

INTRODUCTION

This study aims to describe injury patterns, prehospital interventions and mortality rates of combat-related thoracic injuries during the past decade among Israel Defense Forces (IDF) soldiers before and after implementation of the 2012 IDF-Military Corps 'My Brother's Keeper' plan which included the publication of clinical practice guidelines (CPGs) for thoracic injuries, emphasis on adequate torso protection, introduction of modern life-saving procedures and encouragement of rapid evacuation.

METHODS

The IDF prehospital trauma registry was reviewed to identify all patients who sustained thoracic injuries from January 2006 to December 2017. IDF soldiers who were injured, died of wounds or killed in action (KIA) were included. These were cross-referenced with the Israel National Trauma Registry. The periods before and after the plan were compared.

RESULTS

458 (12.3%) of 3733 IDF soldiers wounded on the battlefield sustained combat-related thoracic injuries. The overall mortality was 44.3% before the CPG and 17.3% after (p<0.001). Most were KIA: 97% (95 of 98) died by 30 June 2012, and 83% (20 of 24) after (p<0.001). Casualties treated with needle thoracostomy before and after CPG were 6.3% and 18.3%, respectively (p=0.002). More tube thoracostomies were performed after June 2012 (16.1% vs 5.4%, p=0.001). Evacuation was faster after June 2012 (119.4 min vs 560.8 min, p<0.001), but the rates of casualties evacuated within 60 min were similar (21.1% vs 25%, p=0.617).

CONCLUSIONS

Among military casualties with thoracic injuries, the rate of life-saving interventions increased, evacuation time decreased and mortality dropped following the implementation of My Brother's Keeper plan.

A Novel Approach to Optimise Length Preservation in Cross Leg Vascular Bridge Flap by AV-Shunting

N/A.

Evaluation of a novel anastomotic device in the animal model: A feasibility, safety, and efficacy study

BACKGROUND

A novel device was designed to assist with microvascular arterial anastomoses. This study compares the safety and efficacy of the anastomosis-assisting device with manual suturing in an ovine model.

METHODS

Arteries with a diameter ranging from 2 to 4 mm were transected and anastomosed at four locations. A comparison was done between manual anastomoses and anastomoses performed with a novel anastomotic device in seven sheep. All the device-assisted anastomoses were performed by a single surgeon. At day 45 ± 7, anastomotic sites were dissected to determine patency, and samples were obtained for pathology.

RESULTS

Thirteen of 13 (100%) samples from the Vesseal™ group demonstrated patency both on the day the anastomoses were performed and after the 45-day follow-up period. All four additional anastomoses performed using the Vesseal™ were found patent. In the hand-suturing group, six of six (100%) samples demonstrated patency on the day of the anastomoses and five of six (83%) were patent after the follow-up period. No thromboses or adverse events were observed in the anastomoses in either group. No difference in histopathology of the anastomoses was observed between the groups.

CONCLUSIONS

The anastomosis-assisting device is a safe and efficacious alternative to hand suturing. The patency rates of device-assisted anastomoses were greater than those of manual suturing and pose no additional risk, as demonstrated by clinical observation, histopathology, and macroscopic evaluation. The Vesseal™ anastomosis-assisting device may be a viable alternative to manual suturing, with an ergonomic and intuitive design, short learning curve, and consistent results.

The association between helicopter emergency medical services and early casualty survival: a nationwide study

BACKGROUND

Helicopter emergency medical services (HEMS) allow for shorter transport duration in long-distance evacuations and facilitate advanced en-route medical care access. Studies comparing HEMS with ground emergency medical services (GEMS), including the outcome of prehospital mortality, are lacking.

OBJECTIVE

This study aimed to evaluate the association between HEMS and early mortality in Israel.

SETTING

A retrospective cohort study was conducted of the cross-referenced Israel Defense Forces Trauma Registry and Israel National Trauma Registry databases.

OUTCOME MEASURES AND ANALYSIS

Univariable logistic regression was used to assess the association between HEMS and early mortality, defined as mortality within 1 day of the injury. Regression analysis was further performed stratifying by event type (military or civilian) or type of injury (penetrating or nonpenetrating).

RESULTS

A total of 2344 casualties were included in the study, of whom 756 (32.3%) were evacuated by air. Early mortality rates were 90/1588 (5.7%) and 37/756 (4.9%) in GEMS and HEMS groups, respectively. Regression analysis found no significant analysis between HEMS and early mortality [OR, 0.86 (95% CI, 0.57-1.26)]. Stratified by event type, a nonsignificant association between HEMS and early mortality was demonstrated for combat [OR, 1.69 (95% CI, 0.79-3.92)] and noncombat [OR, 0.73 (95% CI, 0.4-1.25)] events. HEMS was associated with decreased early mortality among casualties with a penetrating injury [OR, 0.59 (95% CI, 0.34-0.98)] but not associated with early mortality among casualties with a nonpenetrating injury [OR, 0.84 (95% CI, 0.43-1.52)].

CONCLUSION

HEMS was not associated with a decrease in early mortality among trauma casualties in this study encompassing the prehospital and hospital scenes. There was a positive trend and a decrease in mortality from penetrating injuries. Further research to ascertain which casualties benefit from HEMS is warranted and will allow for more precise use of this expensive resource.

Patterns in vehicle-ramming attacks

BACKGROUND

Vehicle-ramming attacks have become a common tactic for terror organizations worldwide. However, the medical implications of vehicle-ramming attacks remain unknown.

OBJECTIVES

To investigate the characteristics of vehicle-ramming attack incidents and casualties in order to assist in guiding the policy of medical organizations.

METHODS

In this study we included all vehicle-ramming attacks recorded in the Israel Defense Forces-Trauma Registry between 2015 and 2019. Records were screened using text mining of incident, casualty, and injury descriptions. The selected records were examined manually to ensure that they were vehicle-ramming attacks. Incident and casualty data were retrieved from the trauma registry.

RESULTS

During the years 2015-2019, a total of 36 vehicle-ramming attacks with 113 casualties were documented in the trauma registry. The median number of casualties, urgent casualties, and fatalities per incident was 3 (interquartile range [IQR] 2-5), 1 (IQR 1-2), and 1 (IQR 1-1), respectively. Of the incidents, 15 (42%) had three or more casualties. The most prevelant day of the week was Friday with 9 incidents (25%). Within the day, 21 incidents (58%) occurred between the hours of 12:00 and 18:00. Commonly injured body regions were lower extremities (55%), head (28%), and upper extremities. Ten victims (9%) died before arriving at a hospital.

CONCLUSIONS

Vehicle-ramming attacks tend to have multiple casualties, be deadly, occur more often on Fridays and in the afternoon, and result mostly in injuries to the extremities and the head. These findings could guide policymaking to improve medical response to vehicle-ramming attacks.

Trends in prehospital pain management: two decades of point-of-injury care

BACKGROUND

Pain control in trauma is an integral part of treatment in combat casualty care. More soldiers injured on the battlefield need analgesics for pain than life-saving interventions (LSIs). Early treatment of pain improves outcomes after injury, while inadequate treatment leads to higher rates of post-traumatic stress disorder (PTSD).

OBJECTIVES

To describe the experience of the Israel Defense Forces (IDF) Medical Corps with prehospital use of analgesia.

METHODS

All cases documented in the IDF-Trauma Registry between January 1997 and December 2019 were examined. Data collection included analgesia administered, mechanism of injury, wound distribution, and life-saving interventions performed.

RESULTS

Of 16,117 patients, 1807 (11.2%) had at least one documented analgesia. Demographics included 91.2% male; median age 21 years. Leading mechanism of injury was penetrating (52.9%). Of injured body regions reported, 46.2% were lower extremity wounds. Most common types of analgesics were morphine (57.2%) and fentanyl (27%). Over the two decades of the study period, types of analgesics given by providers at point of injury (POI) had changed. Fentanyl was introduced in 2013, and by 2019 was given to 39% of patients. Another change was an increase of casualties receiving analgesia from 5-10% until 2010 to 34% by 2019. A total of 824 LSIs were performed on 556 patients (30.8%) receiving analgesia and no adverse events were found in any of the casualties.

CONCLUSIONS

Most casualties at POI did not receive any analgesics. The most common analgesics administered were opioids. Over time analgesic administration has gained acceptance and become more commonplace on the battlefield.

BladeShield 101: A Novel Prehospital Digital Wearable Combat Casualty Card

BACKGROUND

The Israeli Defense Forces-Medical Corps (IDF-MC) focuses on reducing preventable death by improving prehospital trauma care. High quality documentation of care can serve casualty care and to improve future care. Currently, paper casualty cards are used for documentation. Incomplete data acquisition and inadequate data handover are common. To resolve these deficits, the IDF-MC launched the BladeShield 101 project.

OBJECTIVES

To assess the quality of casualty care data acquired by comparing standard paper casualty cards with the BladeShield 101.

METHODS

The BladeShield 101 system consists of three components: a patient unit that records vital signs and medical care provided, a medical sensor that transmits to the patient unit, and a ruggedized mobile device that allows providers to access and document information. We compared all trauma registries of casualties treated between September 2019 and June 2020.

RESULTS

The system was applied during the study period on 24 patients. All data were transferred to the military trauma registry within one day, compared to 72% (141/194) with a paper casualty card (P < 0.01). Information regarding treatment time was available in 100% vs. 43% (P < 0.01) of cases and 98% vs. 67% (P < 0.01) of treatments provided were documented comparing BladeShield 101 with paper cards, respectively.

CONCLUSIONS

Using an autonomous system to record, view, deliver, and store casualty information may resolve most current information flow deficits. This solution will ultimately significantly improve individual patient care and systematic learning and development processes.

Emergent exploratory thoracotomy with military casualties: contemporary prehospital management and outcome (see editorial page 619)

BACKGROUND

Chest trauma is among the most common types of trauma, corresponding to 10% of trauma patients admitted to hospitals. In the military setting, thoracic trauma was reported as a significant cause of death. With well-timed treatment, chest trauma is regarded as survivable. Emergency thoracotomy (ET) is considered when the patient with trauma to the chest needs immediate resuscitation. Survival rate is reported as low as 1% in some reports and 20% in others. The survival rate depends on injury mechanism, protocols for intervention, and other decompressive procedures.

OBJECTIVES

To determine parameters that may impact survival of ET.

METHODS

We conducted a retrospective cohort study to compare prehospital and in-hospital data regarding ET in the emergency department (ED) versus the operating room (OR).

RESULTS

Between 2009 and 2017, 6532 casualties presented to the ED; 1125 with trauma to the chest. Fifty-four of those with chest trauma underwent ET in the hospital (4.8%), 22 (41%) in the ED, and 32 (59%) in the OR. The overall mortality of the ET subgroup was 48%. With regard to thoracotomies, 19/22 of patients (86%) who underwent ET in the ED died compared to 2/28 in the OR (13%).

CONCLUSIONS

Utilizing ET after chest trauma with appropriate clinical indications, well-trained personnel, and prompt transportation poses a significant challenge, but may be associated with better survival than that reported previously with military casualties. Adoption of indications and timed allocation to the OR may improve outcomes with chest trauma casualties.

A prehospital scoring system for predicting the need for emergent blood product transfusion

BACKGROUND

Several tools have been proven to predict the need for massive transfusion in trauma casualties, yet tools that are easily applicable in the prehospital setting for predicting the need for any blood product transfusion in the emergency department (ED) are lacking.

METHODS

A retrospective analysis of the cross-referenced Israeli Defense Forces Trauma Registry and the Israeli National Trauma Registry databases was performed to identify predictors for any blood product transfusion in the ED. A scoring system was developed after internally validating the prediction model. Division to risk groups was performed.

RESULTS

Seven variables (systolic blood pressure, heart rate, arterial oxygen saturation, trunk involvement, mechanism of injury, chest decompression, and tourniquet application) were included in the scoring system, ranging from 0 to 11.5. Risk groups for ED transfusion included very low (0.8%), low (3.2%), intermediate (8.5%), and high (31.2%) risk.

CONCLUSION

A scoring system for predicting the need for any blood product transfusion in the ED was developed, based on information readily available in the early stages of prehospital resuscitation, allowing the receiving medical facility to prepare for that need.

Trends in combat casualty care following the publication of clinical practice guidelines

BACKGROUND

The current study explores the trends in the application of combat casualty care following the publication of clinical practice guidelines (CPGs) in five domains for 13 years.

METHODS

The Israel Defense Forces Trauma Registry was used to assess practice and adherence to guidelines in five domains: (a) crystalloid transfusions, (b) tranexamic acid use, (c) freeze-dried plasma use, (d) chest decompression, and (e) airway management. All patients injured between January 2006 and December 2018 were included in the analysis. Trends were analyzed and presented monthly using linear regression and were compared using the Chow test.

RESULTS

The mean ± SD crystalloid volume transfused decreased from 1,179 ± 653 mL in 2006 to 466 ± 202 mL in 2018 (B = 0.016, 0.006-0.044). The proportion of patients with an indication treated with tranexamic acid dropped from 8% (238 of 2,979 patients) to 2.5% (60 of 2,356 patients) following the stricter guideline's publication. Freeze-dried plasma administration in indicated casualties rose from 12.5% in 2013 to 48% in 2018 (B = 1.63, 1.3-2.05). The overall proportion of casualties undergoing chest decompression rose from 1% (61 of 6,036 casualties) to 1.5% (155 of 10,493 casualties) following the release of a new CPG in 2012 (p = 0.013). There were no significant trends in intubation ratios before (B = 0.987, 0.953-1.02) or after 2012 (B = 10.2, 0.996-1.05).

CONCLUSION

Some aspects demonstrate the desired trends in response to new CPGs; in others, initial improvement is achieved but followed by stagnation. In some medical care aspects, completely unexpected and undesirable trends are observed. Every change and update in CPGs should be based on reliable data. The effect of every change must be monitored carefully to ensure adequate adherence to lifesaving guidelines.

LEVEL OF EVIDENCE

Epidemiological study, level IV.

Medical Challenges in Underground Warfare

INTRODUCTION

Throughout history, underground systems have served military purposes in both offensive and defensive tactical settings. With the advance of underground mining, combat tactics, and weapon systems, providing medical support in the subterranean battlefield is a constantly growing challenge. This retrospective cohort study describes the Israeli Defense Force (IDF) Medical Corps experience with treating casualties from underground warfare, as recorded in the IDF Trauma Registry.

METHODS

A retrospective cohort study of all casualties engaged in underground warfare, between the years 2004-2018. Medical data were extracted from the IDF Trauma Registry and tactical data were obtained from operational reports. An expert committee characterized the most prevalent challenges. Recommendations were based on a literature review and the lessons learned by the IDF experience.

RESULTS

During the study period, 26 casualties were injured in the underground terrain. Of casualties, 12 (46%) due to blast injuries, 9 (35%) were due to smoke inhalation, and 5 (19%) due to crushing injuries. All were males, and the average age was 21.6 years. Ten (38%) were killed in action (died before reaching a medical facility). All 16 casualties reaching the hospital survived (Table I). The expert committee divided the most common challenges into three categories-tactical, environmental, and medical. An overview of medical response planning, common injuries, and designated combat casualty care are discussed below. As in all combat casualty care, the focus should be on safety, bleeding control, and rapid evacuation.

CONCLUSION

To plan and provide medical support, a thorough understanding of operational planning is essential. This manuscript presents the evolution of underground warfare, tactical and medical implications, environmental hazards, and common casualty care challenges.

Pausing cancer screening during the severe acute respiratory syndrome coronavirus 2pandemic: Should we revisit the recommendations?

•The outbreak of severe acute respiratory syndrome coronavirus has become a global major concern. •Medical professionals were instructed to use their clinical judgement when scheduling elective activity. •Delays in cancer screening, should not go unnoticed and this ‘knee-jerk’ response should be revisited. •If the current situation last, we anticipate that thousands of cases will be diagnosed late or missed.

Prevalence of Iron Deficiency and Iron Deficiency Anemia in Strenuously Training Male Army Recruits

OBJECTIVES

The objectives of our study were to determine the effect of strenuous physical training on the prevalence of iron deficiency anemia (IDA), iron deficiency (ID) with normal hemoglobin (Hb), and anemia without ID.

METHODS

Our study was a prospective observational study. We followed 115 healthy male recruits in the Israel Defense Forces elite units during 15 months of training. Blood samples were collected at recruitment and at 6-, 9- and 15-month follow-ups.

RESULTS

Upon recruitment, anemia (Hb < 14 g/dL), ID, and ID anemia (IDA) were diagnosed in 28, 31, and 9% of individuals, respectively. Sixty-three subjects (54%) were followed for 6 months; 9 of them (14%) developed new-onset IDA. Among them, the prevalence of anemia rose from 19 to 52%, and ID from 33 to 35%. At the 15-month follow-up, 29% had developed new-onset IDA and 65% showed evidence of ID.

CONCLUSION

We report a high prevalence of anemia, ID, and IDA among young healthy males participating in prolonged strenuous training programs. These findings can be partly explained by the physiological changes associated with strenuous physical activity. Further investigations aiming to develop specific diagnostic guidelines for this unique population are warranted.

The search for the best infantry boot

BACKGROUND

The combat role of the twenty-first century infantry soldier has changed and accordingly their boots should evolve to meet these new needs and maximize soldier performance.

OBJECTIVE

To evaluate injuries and durability of the hot weather infantry boots (HWIB) in elite infantry training and assess the initial performance of newly designed Israeli infantry boots (NDIB).

METHODS

In Phase 1, the durability of the HWIB during elite infantry training was evaluated at weeks 10, 19 and 64 in a cohort of 67 recruits. At each exam recruits removed their boots which were assessed for wear and integrity and photographed. The number of times recruits changed their boots was recorded. In Phase 2, foot injuries were assessed in a cohort of 73 elite infantry recruits wearing HWIB. In Phase 3, 65 infantry recruits were issued the NDIB. Recruits feet were measured for width and shoe size using the Brannock device and then followed for problems associated with their boots. Foot lesions were document by photographs.

RESULTS

Phase 1: The mean longevity of HWIB in training was 5.2 ± 0.2 (SE) months, (95 % CI 4.83-5.61). Phase 2: 38 % of the elite infantry recruits wearing HWIB had at least one complaint and 31 (42 %) were found to have boot related injuries in a total of 56 injured areas. Phase 3: The mean predicted boot size (42.8 ± 1.7) based on Brannock measurements, was less than the size of the NDIB actually worn, 43.1 ± 1.6. Only 34.8 % of the feet were width D (the standard shoe width). At 9 day follow up, 55 of the 65 recruits who wore NDIB reported at least one problem with them (85 %, p < 0.0001, compared to HWIB). By 3 weeks, all but five recruits had returned to wearing the HWIB. Of the recruits wearing NDIB, 47 (72 %) were found to have had at least one boot related injury with a total number of 180 injured foot areas (p = 0.0004, compared to HWIB).

CONCLUSIONS

The HWIB was well tolerated by the elite infantry recruits and associated with significantly less foot injuries than the NDIB. The longevity of the HWIB in demanding elite infantry training was five months. Trial registration: NCT02810002 retrospectively registered June 22, 2016.

Testing of Junctional Tourniquets by Medics of the Israeli Defense Force in Control of Simulated Groin Hemorrhage

BACKGROUND

Junctional hemorrhage is a common cause of battlefield death but little is known about testing of junctional tourniquet models by medics. The purpose of the testing described herein is to assess military experience in junctional tourniquet use in simulated prehospital care.

METHODS

Fourteen medics were to use the following four junctional tourniquets: Combat Ready Clamp (CRoC), Abdominal Aortic Junctional Tourniquet (AAJT), Junctional Emergency Treatment Tool (JETT), and SAM Junctional Tourniquet (SJT). The five assessment categories were safety, effectiveness, time to effectiveness, and two categories of user preference: (1) by all models assessed, and (2) by only the model most preferred. Users ranked preference by answering, "If you had to go to war today and you could only choose one, which tourniquet would you choose to bring?"

RESULTS

All tourniquet uses were safe. By the time the first five testers were done, all three AAJT models had been broken. CRoC and AAJT had the highest percentage effectiveness as their difference was not statistically significant. SJT and JETT had fastest mean times to effectiveness as their difference was not significant. For preference, using each user's ranking of all models assessed, SJT and AAJT were most preferred as their difference was not significant. For each user's most preferred model, SJT, AAJT, and JETT were most preferred as their difference was not significant.

CONCLUSION

In the five assessment categories, multiple tourniquet models performed similarly well; SJT and AAJT performed best in four categories, JETT was best in three, and CRoC was best in two. Differences between the top-ranked models in each category were not statistically significant.

Rapid regulation of dopamine transporters by tyrosine kinases in rat neuronal preparations

Termination of dopamine neurotransmission is primarily controlled by the plasma membrane-localized dopamine transporter. In this study, we investigated how this transporter is regulated by tyrosine kinases in neuronal preparations. In rat dorsal striatal synaptosomes, inhibition of tyrosine kinases by genistein or tyrphostin 23 resulted in a rapid (5-15 min), concentration-dependent decrease in [(3)H]dopamine uptake because of a reduction in maximal [(3)H]dopamine uptake velocity and dopamine transporter cell surface expression. The reduced transporter activity was associated with a decrease in phosphorylated p44/p42 mitogen-activated protein kinases. In primary rat mesencephalic neuronal cultures, the tyrosine kinase inhibitors similarly reduced [(3)H]dopamine uptake. When cultures were serum-deprived, acute activation of tyrosine kinase-coupled TrkB receptors by 100 ng/mL brain-derived neurotrophic factor significantly increased [(3)H]dopamine uptake; the effects were complex with increased maximal velocity but reduced affinity. The facilitatory effect of brain-derived neurotrophic factor on dopamine transporter activity depended on both the mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways. Taken together, our results suggest that striatal dopamine transporter function and cell surface expression is constitutively up-regulated by tyrosine kinase activation and that brain-derived neurotrophic factor can mediate this type of rapid regulation.

Trafficking of yellow-fluorescent-protein-tagged mu1 subunit of clathrin adaptor AP-1 complex in living cells

Clathrin adaptor protein AP-1 complex is thought to function in forming clathrin-coated vesicles at the trans-Golgi network (TGN) and mediating transport of cargo between the TGN and endosomes. To study trafficking of AP-1 in living cells, yellow fluorescent protein (YFP) was inserted in the middle of mu1 A subunit of AP-1. When expressed in a tetracycline-dependent manner in HeLa cells, YFP-mu1 was efficiently incorporated into the AP-1 complex, replacing endogenous mu1 in most of cellular AP-1. Time-lapse imaging revealed that YFP-mu1/AP-1 departs from TGN as isolated vesicles and spherical structures, or varicosities, associated with fine tubular processes. Typically, several vesicles or varicosities were seen moving sequentially along the same 'tracks' from TGN to cell periphery. These data suggest that AP-1 may function after formation of Golgi transport intermediates in facilitating their intracellular movement. Mutagenesis of YFP-mu1 determined that the structural requirements for its binding to tyrosine-containing sequence motifs are similar to those previously defined in mu2 subunit of AP-2. Moreover, the carboxyl-terminal half of mu2 could replace the corresponding fragment of mu1 without loss of the ability of the resulting mu1-YFP-mu2 chimeric protein to incorporate into AP-1 and bind tyrosine-containing motifs. Mutations that abolish binding capacity for tyrosine motifs did not mistarget AP-1 in the cell, suggesting that AP-1 interactions with this type of sorting signals are not essential for membrane docking of AP-1 at the TGN. Altogether, this study demonstrates that YFP-tagged mu1 protein can serve as a useful tool for visualizing the dynamics of AP-1 in living cells and for the structure-function analysis of mu1-cargo interactions.

Internalization of the epidermal growth factor receptor: role in signalling

The interaction of the activated epidermal growth factor (EGF) receptor (EGFR) with the Src homology 2 (SH2) domain of Grb2 (growth-factor-receptor-bound protein 2) initiates signalling through Ras and mitogen-activated protein kinase. Grb2 can bind EGFR directly or through another SH2-containing protein, Shc. Activation of EGFRs by ligand also triggers rapid endocytosis of EGF-receptor complexes. To analyse the spatial and temporal regulation of EGFR interactions with SH2 domains in living cells, we have combined imaging microscopy with a modified method of measuring fluorescence resonance energy transfer (FRET) on a pixel-by-pixel basis using EGFR fused to cyan fluorescent protein (CFP) in pair with Grb2 or Shc fused to yellow fluorescent protein (YFP). Stimulation by EGF resulted in the recruitment of Grb2-YFP and YFP-Shc to cellular compartments that contained EGFR-CFP, and a large increase in the FRET signal. In particular, FRET measurements indicated that activated EGFR-CFP interacted with YFP-Shc and Grb2-YFP in membrane ruffles and endosomes. These results demonstrate that signalling via EGFRs can occur in the endosomal compartment. Moreover, in contrast with previous biochemical studies, FRET experiments show that a large pool of Grb2 and Shc is associated with EGFRs for a prolonged period after EGF stimulation.

Cost of immunization with a locally produced, oral cholera vaccine in Viet Nam

Policy decisions regarding whether to incorporate new vaccines into routine public health practice in developing countries will depend in part on the costs of vaccine purchase and of vaccine delivery. In March, 1997, a large-scale effectiveness trial of a locally produced, orally administered bivalent vaccine against Vibrio cholerae 01 and 0139 began in Viet Nam. Empirical data obtained from the trial was used to determine the costs of the immunization campaign from the government perspective. The study population, including the children less than one year of age and pregnant women who were ineligible for immunization, was 353926. A total of 289041 persons received two doses of vaccine, and 13340 persons received one dose of vaccine. Two-dose vaccine coverage was 83.4%. The total cost of vaccine delivery during the immunization campaign was $66527. The cost of each dose of vaccine was $0.31. Therefore, the total cost of the immunization campaign was $0.44 per dose administered, and $0.91 per fully immunized person. Attempts to reduce the cost per dose of vaccine (e.g. the use of a monovalent vaccine against serogroup 01) are likely to have a large impact on the cost of future similar immunization campaigns.

Persistent interactions between the two transmembrane clusters dictate the targeting and functional assembly of adenylyl cyclase

Adenylyl cyclases possess complex structures like those of the ATP binding cassette (ABC) transporter family, which includes the cystic fibrosis transmembrane regulator, the P-glycoprotein, and ATP-sensitive K(+) channels [1-4]. These structures comprise a cytosolic N terminus followed by two tandem six-transmembrane cassettes, each associated with a highly homologous (ATP binding) cytosolic loop [5-8]. The catalytic domains, which are located in the two large cytoplasmic loops, are highly conserved and well studied. The crystal structure of these domains has even been described recently [9, 10]. However, nothing is known of the function or organization of the 12 transmembrane segments. In the present study we adopted a range of strategies including live-cell fluorescence resonance energy transfer (FRET) microscopy, coimmunoprecipitation, and functional assays of various truncated and substituted, fluorescently-tagged molecules to analyze the trafficking and activity of this molecule. When expressed as individual peptides, the two transmembrane domains - largely independently of any cytosolic region - formed a tight complex that was delivered to the plasma membrane. This cooperation between the two intact transmembrane domains was essential and sufficient to target the enzyme to the plasma membrane of the cell. The extracellular loop between the ninth and tenth transmembrane segments, which contains an N-glycosylation site, was also necessary. Furthermore, the interaction between the two transmembrane clusters played a critical role in bringing together the cytosolic catalytic domains to express functional adenylyl cyclase activity in the intact cell.

Interaction of EGF receptor and grb2 in living cells visualized by fluorescence resonance energy transfer (FRET) microscopy

The interaction of activated epidermal growth factor receptor (EGFR) with the Src homology 2 (SH2) domain of the growth-factor-receptor binding protein Grb2 initiates signaling through Ras and mitogen-activated protein kinase (MAP kinase) [1,2]. Activation of EGFRs by ligand also triggers rapid endocytosis of EGF-receptor complexes. To analyze the spatiotemporal regulation of EGFR-Grb2 interactions in living cells, we have combined imaging microscopy with a modified method of measuring fluorescence resonance energy transfer (FRET) on a pixel-by-pixel basis using EGFR fused to cyan fluorescent protein (CFP) and Grb2 fused to yellow fluorescent protein (YFP). Efficient energy transfer between CFP and YFP should only occur if CFP and YFP are less than 50A apart, which requires direct interaction of the EGFR and Grb2 fused to these fluorescent moieties [3]. Stimulation by EGF resulted in the recruitment of Grb2-YFP to cellular compartments that contained EGFR-CFP and a large increase in FRET signal amplitude. In particular, FRET measurements indicated that activated EGFR-CFP interacted with Grb2-YFP in membrane ruffles and endosomes. These results demonstrate that signaling via EGFRs can occur in the endosomal compartment. The work also highlights the potential of FRET microscopy in the study of subcellular compartmentalization of protein-protein interactions in living cells.

RLIP76, an effector of the GTPase Ral, interacts with the AP2 complex: involvement of the Ral pathway in receptor endocytosis

RLIP76 is a modular protein that was identified as a putative effector of Ral, a GTPase activated during Ras signaling. To explore further the contribution of the Ral-RLIP76 pathway to Ras signaling, we have looked for partners of RLIP76. Mu2, the medium chain of the AP2 complex is shown to interact with RLIP76. We show also that in vivo endogenous AP2 and RLIP76 form a complex and that this in vivo interaction is independent of cells being stimulated by a growth factor. Furthermore, RLIP76 differentiates AP2 from AP1 in vivo as RLIP76 differentiates mu2 from mu1 in vitro and in two hybrid assays. We show that activated Ral interferes with both tranferrin receptor endocytosis and epidermal growth factor (EGF) receptor endocytosis in HeLa cells. We propose a model where the Ral-RLIP76 pathway connects signal transduction and endocytosis through interaction on one hand between the Ras-Ral pathway and RLIP, on the other hand between RLIP and proteins belonging to the endocytotic machinery.

Clathrin assembly lymphoid myeloid leukemia (CALM) protein: localization in endocytic-coated pits, interactions with clathrin, and the impact of overexpression on clathrin-mediated traffic

The clathrin assembly lymphoid myeloid leukemia (CALM) gene encodes a putative homologue of the clathrin assembly synaptic protein AP180. Hence the biochemical properties, the subcellular localization, and the role in endocytosis of a CALM protein were studied. In vitro binding and coimmunoprecipitation demonstrated that the clathrin heavy chain is the major binding partner of CALM. The bulk of cellular CALM was associated with the membrane fractions of the cell and localized to clathrin-coated areas of the plasma membrane. In the membrane fraction, CALM was present at near stoichiometric amounts relative to clathrin. To perform structure-function analysis of CALM, we engineered chimeric fusion proteins of CALM and its fragments with the green fluorescent protein (GFP). GFP-CALM was targeted to the plasma membrane-coated pits and also found colocalized with clathrin in the Golgi area. High levels of expression of GFP-CALM or its fragments with clathrin-binding activity inhibited the endocytosis of transferrin and epidermal growth factor receptors and altered the steady-state distribution of the mannose-6-phosphate receptor in the cell. In addition, GFP-CALM overexpression caused the loss of clathrin accumulation in the trans-Golgi network area, whereas the localization of the clathrin adaptor protein complex 1 in the trans-Golgi network remained unaffected. The ability of the GFP-tagged fragments of CALM to affect clathrin-mediated processes correlated with the targeting of the fragments to clathrin-coated areas and their clathrin-binding capacities. Clathrin-CALM interaction seems to be regulated by multiple contact interfaces. The C-terminal part of CALM binds clathrin heavy chain, although the full-length protein exhibited maximal ability for interaction. Altogether, the data suggest that CALM is an important component of coated pit internalization machinery, possibly involved in the regulation of clathrin recruitment to the membrane and/or the formation of the coated pit.

Inhibition of the receptor-binding function of clathrin adaptor protein AP-2 by dominant-negative mutant mu2 subunit and its effects on endocytosis

Although interactions between the mu2 subunit of the clathrin adaptor protein complex AP-2 and tyrosine-based internalization motifs have been implicated in the selective recruitment of cargo molecules into coated pits, the functional significance of this interaction for endocytosis of many types of membrane proteins remains unclear. To analyze the function of mu2-receptor interactions, we constructed an epitope-tagged mu2 that incorporates into AP-2 and is targeted to coated pits. Mutational analysis revealed that Asp176 and Trp421 of mu2 are involved in the interaction with internalization motifs of TGN38 and epidermal growth factor (EGF) receptor. Inducible overexpression of mutant mu2, in which these two residues were changed to alanines, resulted in metabolic replacement of endogenous mu2 in AP-2 complexes and complete abrogation of AP-2 interaction with the tyrosine-based internalization motifs. As a consequence, endocytosis of the transferrin receptor was severely impaired. In contrast, internalization of the EGF receptor was not affected. These results demonstrate the potential usefulness of the dominant-interfering approach for functional analysis of the adaptor protein family, and indicate that clathrin-mediated endocytosis may proceed in both a mu2-dependent and -independent manner.

Clathrin, adaptors and eps15 in endosomes containing activated epidermal growth factor receptors

Activation of the epidermal growth factor receptor (EGFR) by EGF results in binding of clathrin adaptor protein complex AP-2 to the receptor cytoplasmic tail. The transient interaction with AP-2 is thought to be responsible for the selective recruitment of the EGFR into coated pits during endocytosis. In this study we found that EGF-induced EGFR/AP-2 association, measured by co-immunoprecipitation, persists after receptor internalization. Double-label immunofluorescence of EGF-treated A-431 and COS-1 cells revealed the presence of AP-2, clathrin and eps15, another component of the plasma membrane coated pits, in the large perinuclear endosomes loaded with EGFRs. By optical sectioning and image deconvolution, the immunoreactivities were seen to be distributed within vesicular and tubular elements of these endosomes. In addition, these compartments contained the transferrin receptors and a EEA.1 protein, markers of early endosomes. Furthermore, Golgi clathrin adaptor complex AP-1 was found in EGFR-containing endosomes and EGFR immunoprecipitates in A-431 cells. The direct interaction of the EGFR with micro1 as well as micro2 subunits of AP-1 and AP-2, correspondingly, was shown using the yeast two-hybrid assay. Brefeldin A, a drug that releases AP-1 from the trans-Golgi membranes, had no effect on AP-1 association with endosomes and its co-precipitation with EGFR. Taken together, the data suggest that endosomal EGFR-AP complexes make up a significant portion of the total amount of these complexes detectable by co-immunoprecipitation. It can be proposed that APs are capable of binding to the endosomal membrane via a mechanism that requires AP interaction with the intracellular tails of multimeric receptors like activated EGFR, which in turn allows recruitment of clathrin and eps15. The hypothesis that the competition between adaptor complexes for binding to the receptor tails in endosomes may regulate of the sorting of receptors is discussed.

Endocytosis of functional epidermal growth factor receptor-green fluorescent protein chimera

A chimera of the epidermal growth factor receptor (EGFR) and green fluorescent protein (GFP) has been engineered by fusing GFP to the carboxyl terminus of EGFR. Data are provided to demonstrate that the GFP moiety does not affect the expected functioning of EGFR. EGFR-GFP becomes phosphorylated at tyrosine residues in response to EGF and is capable of phosphorylating endogenous substrates and initiating signaling cascades. EGF-dependent association of the chimeric receptor with the clathrin adaptor protein AP-2, involved in endocytosis, and with Shc adaptor protein, which binds in close proximity to the fusion point, is not affected by the GFP moiety. Receptor down-regulation and internalization occur at rates similar to those in cells expressing wild-type EGFR. Western blot analysis reveals that lysosomal degradation of EGFR-GFP proceeds from the extracellular domain and that GFP is not preferentially cleaved. Time-dependent co-localization of EGFR-GFP and Texas Red-conjugated EGF in living cells using digital deconvolution microscopy demonstrates the trafficking of ligand-receptor complexes through the early and multivesicular endosomes followed by segregation of the ligand and receptor at the late stages of endocytosis. Time-lapse optical analysis of the early stages of endocytosis reveals localization of EGFR-GFP in the tubular-vesicular endosomal compartments. Rapid dynamics of membrane movement and fusion within these compartments were observed. This approach and the fidelity of the biochemical properties of the EGFR-GFP demonstrate that real-time visualization of trafficking and protein interactions of tyrosine kinase receptors in the presence or absence of the ligand are feasible.

Structure and Asn-Pro-Phe binding pocket of the Eps15 homology domain

Eps15 homology (EH) domains are eukaryotic signaling modules that recognize proteins containing Asn-Pro-Phe (NPF) sequences. The structure of the central EH domain of Eps15 has been solved by heteronuclear magnetic resonance spectroscopy. The fold consists of a pair of EF hand motifs, the second of which binds tightly to calcium. The NPF peptide is bound in a hydrophobic pocket between two alpha helices, and binding is mediated by a critical aromatic interaction as revealed by structure-based mutagenesis. The fold is predicted to be highly conserved among 30 identified EH domains and provides a structural basis for defining EH-mediated events in protein trafficking and growth factor signaling.

Treatment and vaccination strategies to control cholera in sub-Saharan refugee settings: a cost-effectiveness analysis

CONTEXT

There is significant controversy about how best to control cholera epidemics in refugee settings. Specifically, there is marked disagreement about whether to use oral cholera vaccines in these settings, despite the improved safety and effectiveness profiles of these vaccines.

OBJECTIVE

To determine the cost-effectiveness of alternative intervention strategies, including vaccination, to control cholera outbreaks in sub-Saharan refugee camps.

DESIGN

A cost-effectiveness analysis based on probabilities of cholera outcomes derived from epidemiologic data compiled for refugee settings in Malawi from 1987 through 1993; data for costs were obtained from a large relief agency that provides medical care in such settings.

SETTING AND PARTICIPANTS

A hypothetical refugee camp with 50000 persons in sub-Saharan Africa evaluated for a 2-year period.

INTERVENTIONS

We compared the costs and outcomes of alternative strategies in which appropriate rehydration therapy for cholera is introduced preemptively (at the establishment of a camp) or reactively (once an epidemic is recognized) and in which mass immunization with oral B subunit killed whole-cell (BS-WC) cholera vaccine is added to a rehydration program either preemptively or reactively.

MAIN OUTCOME MEASURES

Cost per cholera case prevented and cost per cholera death averted.

RESULTS

In a situation with no available rehydration therapy suitable for the management of severe cholera, a strategy of preemptive therapy ($320 per death averted) costs less and is more effective than a strategy of reactive therapy ($586 per death averted). Adding vaccination to preemptive therapy is expensive: $1745 per additional death averted for preemptive vaccination and $3833 per additional death averted for reactive vaccination. However, if the cost of vaccine falls below $0.22 per dose, strategies combining vaccination and preemptive therapy become more cost-effective than therapy alone.

CONCLUSIONS

Provision for managing cholera outbreaks at the inception of a refugee camp (preemptive therapy) is the most cost-effective strategy for controlling cholera outbreaks in sub-Saharan refugee settings. Should the price of BS-WC cholera vaccine fall below $0.22 per dose, however, supplementation of preemptive therapy with mass vaccination will become a cost-effective option.

Eps15R is a tyrosine kinase substrate with characteristics of a docking protein possibly involved in coated pits-mediated internalization

eps15R was identified because of its relatedness to eps15, a gene encoding a tyrosine kinase substrate bearing a novel protein-protein interaction domain, called EH. In this paper, we report a biochemical characterization of the eps15R gene product(s). In NIH-3T3 cells, three proteins of 125, 108, and 76 kDa were specifically recognized by anti-eps15R sera. The 125-kDa species is a bona fide product of the eps15R gene, whereas p108 and p76 are most likely products of alternative splicing events. Eps15R protein(s) are tyrosine-phosphorylated following epidermal growth factor receptor activation in NIH-3T3 cells overexpressing the receptor, even at low levels of receptor occupancy, thus behaving as physiological substrates. A role for eps15R in clathrin-mediated endocytosis is suggested by its localization in plasma membrane-coated pits and in vivo association to the coated pits' adapter protein AP-2. Finally, we demonstrate that a sizable fraction of eps15R exists in the cell as a complex with eps15 and that its EH domains exhibit binding specificities that are partially distinct from those of eps15. We propose that eps15 and eps15R are multifunctional binding proteins that serve pleiotropic functions within the cell.

Eps15 is constitutively oligomerized due to homophilic interaction of its coiled-coil region

Eps15 is a member of an emerging family of proteins containing a novel protein/protein interaction domain, the EH domain, of as yet unknown function. Recent findings of Eps15 association with clathrin adaptor complex AP-2 and its localization in clathrin-coated pits have implicated Eps15 in the regulation of vesicle trafficking. Here we show that Eps15 exists in several multimeric states in vivo. When purified recombinant Eps15 or lysates of NIH 3T3 cells were treated with cross-linking reagents, covalent dimers of Eps15 and larger covalent multimers were detected in high yield. Large Eps15 oligomers co-immunoprecipitated with AP-2 at an efficiency higher than that of Eps15 dimers. Furthermore, cross-linking of the membrane-bound fraction of Eps15 in mildly permeabilized cells was as efficient as that of the cytosolic fraction. Size-exclusion column chromatography of recombinantly produced Eps15 and of total cell lysates was performed to examine the equilibrium ratio of the monomers versus the aggregated forms of Eps15. These experiments showed that essentially all the Eps15 was aggregated, whereas monomers of Eps15 could be obtained only under strong denaturing conditions. To map the region of Eps15 responsible for dimerization, fusion proteins corresponding to the three structural domains of Eps15 were prepared. Cross-linking analysis revealed that the central portion of Eps15, which possesses a coiled-coil region (residues 321-520), serves as the interacting interface. The possibility that hetero-oligomeric complexes of Eps15 dimers and AP-2 function during the recruitment of proteins into coated pits is discussed.

Lysosomal targeting of epidermal growth factor receptors via a kinase-dependent pathway is mediated by the receptor carboxyl-terminal residues 1022-1123

Binding of epidermal growth factor (EGF) to its receptor induces rapid internalization and degradation of both ligand and receptor via the lysosomal pathway. To study the mechanism of intracellular sorting of EGF-EGF receptor complexes to lysosomes, NIH 3T3 cells transfected with wild-type and mutant EGF receptors were employed. The kinetics of 125I-EGF trafficking was analyzed using low concentrations of the ligand to avoid saturation of the specific sorting system. The relative size of the pool of internalized 125I-EGF-receptor complexes that were capable of recycling decreased as receptors traversed the endosomal system. The rate of 125I-EGF sequestration from the recycling pathway correlated with the rate of 125I-EGF transition from early to late endosomes as measured by Percoll gradient fractionation. Deletion of the last 63 amino acids of the EGF receptor cytoplasmic tail did not inhibit the process of sequestration and targeting to the late endosomes and lysosomes. Truncation of the 123 residues, however, resulted in impaired lysosomal targeting and increased recycling of EGF. Receptor mutant in which 165 residues were deleted displayed maximal ability to recycle and a minimal extent of sorting to the late endosomes. The data suggest that two regions of the EGF receptor molecule, residues 1022-1063 and to a lesser extent residues 1063-1123, contribute in the regulation of routing of EGF receptors to the degradation pathway. The kinase-negative receptor mutant recycled EGF more intensively compared with the wild-type receptor, and the transport of this mutant to late endosomes was inhibited. These results support the view that the receptor kinase activity is important for ligand-induced sorting of EGF receptors to the pathway of lysosomal degradation.

Eps15 is a component of clathrin-coated pits and vesicles and is located at the rim of coated pits

Eps15, a phosphorylation substrate of the epidermal growth factor (EGF) receptor kinase, has been shown to bind to the alpha-subunit of the clathrin-associated protein complex AP-2. Here we report that in cells, virtually all Eps15 interacts with the cytosol and membrane-bound forms of AP-2. This association is not affected by the treatment of cells with EGF. Immunofluorescence microscopy reveals nearly absolute co-localization of Eps15 with AP-2 and clathrin, and analysis by immunoelectron microscopy shows that the localization of membrane-associated Eps15 is restricted to the profiles corresponding to endocytic coated pits and vesicles. Unexpectedly, Eps15 was found at the edge of forming coated pits and at the rim of budding coated vesicles. This asymmetric distribution is in sharp contrast to the localization of AP-2 that shows an even distribution along the same types of clathrin-coated structures. These findings suggest several possible regulatory roles of Eps15 during the formation of coated pits.

Epidermal growth factor receptor interaction with clathrin adaptors is mediated by the Tyr974-containing internalization motif

The carboxyl-terminal regulatory domain of the epidermal growth factor (EGF) receptor is essential for its endocytosis and interaction with the clathrin-associated protein complex AP-2. To identify AP-2 binding motif in the receptor, several single and multiple-point mutations within the region between residues 966 and 977 of the human EGF receptor were made, and the mutant receptors were expressed in NIH3T3 cells. Mutation of tyrosine 974 alone or together with surrounding residues and the deletion of residues 973-975 essentially eliminated AP-2 co-immunoprecipitation with the EGF receptor. Furthermore, a synthetic peptide corresponding to receptor residues 964-978 blocked AP-2 association with the wild-type EGF receptor. These data suggest that AP-2 has only one high-affinity binding site in the EGF receptor composed of Tyr974-containing motif. Receptor mutants that did not bind AP-2 displayed a lower rate of internalization, down-regulation, and turnover compared to wild-type receptors when expressed at high levels. However, similar receptor mutants expressed at low levels were internalized and down-regulated as efficiently as wild-type receptors. Internalization of the mutant receptors lacking the high-affinity binding site for AP-2 was inhibited by K+-depletion of the cells, indicating that their endocytosis required intact coated pits. We suggest that whereas one mechanism of EGF receptor recruitment into coated pits involves high-affinity binding of AP-2 to Tyr974-containing motif, another pathway may be mediated by weak receptor/AP-2 interactions or by proteins other than AP-2.

Stoichiometric interaction of the epidermal growth factor receptor with the clathrin-associated protein complex AP-2

Plasma membrane clathrin-associated protein complexes (AP-2) have been shown to co-immunoprecipitate with the epidermal growth factor (EGF) receptor (Sorkin A., and Carpenter, G. (1993) Science 261, 612-615). Hence, we analyzed the stoichiometry of the EGF receptor interaction with AP-2 using a new antibody that efficiently immunoprecipitates native AP-2. EGF receptor AP-2 complexes were isolated from 35S-labeled cells treated with EGF by EGF receptor affinity chromatography followed by precipitation with the antibody to AP-2. Quantitation of the relative molar concentrations of the proteins found in the complex revealed that 1 mol of AP-2 was associated with approximately 1.1 mol of EGF receptor. No other proteins were present in significant molar concentrations relative to AP-2, indicating that other proteins are not stoichiometrically involved in the interaction of EGF receptors and AP-2 in vivo. Co-immunoprecipitation experiments in cells expressing a mutant EGF receptor demonstrated that the cytoplasmic carboxyl-terminal 214 residues of the EGF receptor are essential for interaction with AP-2.

Direct and indirect cost of percutaneous transluminal coronary angioplasty

A prospective study of 53 patients employed in the 6-month period before coronary angioplasty was performed to determine the direct and indirect costs of lag time in work resumption. The total direct costs calculated were $273,480; indirect costs for this sample were $150,944. When these costs are generalized to all patients in the US undergoing uncomplicated percutaneous transluminal coronary angioplasty, the costs are more than $1.2 billion. This study demonstrated that even in patients with a high a priori probability of work return, delay in work resumption results in a greater cost to the individual and society through absence from the labor force.

The carboxyl terminus of epidermal growth factor receptor/erbB-2 chimerae is internalization impaired

The endocytosis of gp185erbB-2 was studied using chimeric receptors in which the intracellular domain of erbB-2, or subdomins thereof, was substituted for the corresponding regions of the epidermal growth factor (EGF) receptor. Chimeric and wild-type EGF or erbB-2 receptors were expressed in mouse NIH3T3 or NR6 fibroblasts and in a human mammary adenocarcinoma cell line, MDAMB-134. The rate of EGF-induced internalization for the chimera consisting of the extracellular EGF receptor domain and intracellular erbB-2 domain was reduced three- to fourfold compared with the wild-type EGF receptor. The low rate of internalization of the chimeric receptor resulted in impaired down-regulation and degradation of the receptor. Substitution of the carboxyl terminus of erbB-2 for the corresponding region of the EGF receptor caused a similar decrease of receptor endocytosis, whereas substitution of the erbB-2 tyrosine kinase domain did not affect internalization and down-regulation. Since the tyrosine kinase of the internalization-defective chimeric receptors could be activated by EGF, kinase activity and autophosphorylation of erbB-2 do not appear to be sufficient for a maximum rapid internalization of the chimeric receptors. These results suggest that the carboxyl terminus of erbB-2 either does not possess all the signals required for the rapid internalization or contains an inhibitory signal for rapid internalization.

Tyrosine phosphorylation of ras GTPase-activating protein does not require association with the epidermal growth factor receptor

The importance of the carboxyl-terminal domain of the epidermal growth factor (EGF) receptor and its five autophosphorylation sites in the in vivo interaction and tyrosine phosphorylation of the ras GTPase-activating protein (rasGAP) has been investigated, using NIH 3T3 cells transfected with mutant EGF receptors. Phosphorylation of rasGAP by EGF receptor mutants, in which one to four autophosphorylation sites (Tyr-1173, -1148, -1086, and -1068) were mutated to phenylalanine, was reduced by 50-60% compared to the wild-type receptor. Elimination of these four autophosphorylation sites by truncation of 123 carboxyl-terminal residues of the EGF receptor paralleled results obtained with point mutants. Substantial inhibition (about 90%) of rasGAP tyrosine phosphorylation by the EGF receptor occurred only when the remaining autophosphorylation site (Tyr-992) was mutated, in the context of this truncated receptor or in the full-length receptor mutated at all four other autophosphorylation sites. However, a point mutation of only Tyr-992 in the full-length receptor suppressed tyrosine phosphorylation of rasGAP only by 50%. In contrast, an EGF receptor lacking the last 214 amino acid residues (Dc214), which encompasses all five autophosphorylation sites, phosphorylated rasGAP to the same extent as the wild-type receptor. However, this truncated receptor was significantly impaired in its capacity to phosphorylate phospholipase C-gamma 1. Interestingly, while EGF receptor autophosphorylation sites are required for EGF-induced rasGAP association with the receptor, maximal phosphorylation of rasGAP by the truncated receptor Dc214 occurred without detectable formation of receptor-rasGAP complexes. Furthermore, the capacity of mutated EGF receptors to bring about focal transformation was correlated with their capacity to phosphorylate rasGAP.

Pool of ligand-bound platelet-derived growth factor beta-receptors remain activated and tyrosine phosphorylated after internalization

We have examined the state of tyrosine phosphorylation of ligand-bound, internalized platelet-derived growth factor (PDGF) beta-receptors. Analysis by immunofluorescence staining of cells stimulated with PDGF-BB at 37 degrees C indicated colocalization of phosphotyrosine, PDGF beta-receptors, and PDGF-BB in endosome-like vesicles. Treatment of cells with an acidic buffer, which removed cell surface-bound PDGF-BB, led to a considerable decrease in phosphorylation and kinase activity of cell surface localized PDGF beta-receptors, but not of internalized receptors. Immunoprecipitations using antisera against phosphotyrosine and the PDGF beta-receptor from metabolically labeled cells showed that a major fraction of the tyrosine-phosphorylated pool of receptors were still accessible to the acid buffer treatment after 10 min of incubation of the cells at 37 degrees C. Under these conditions, about 20-25% of the total pool of tyrosine-phosphorylated receptors were intracellular, since they remained tyrosine phosphorylated after the acid buffer treatment. A considerable pool of tyrosine-phosphorylated, internalized receptors, after 10 min of incubation of the cells at 37 degrees C, could also be detected by immunoblotting analysis, using antisera against the PDGF beta-receptor and phosphotyrosine. Analysis by in vitro kinase assays of immunoprecipitated PDGF beta-receptors, obtained from PDGF-BB-stimulated cells different times after acid wash, showed that the internalized receptors retained kinase activity. These data suggest that a pool of internalized PDGF beta-receptors remain active and may participate in signalling a considerable time after internalization.

Interaction of activated EGF receptors with coated pit adaptins

The epidermal growth factor (EGF) receptor interacts with plasma membrane-associated adapter proteins during endocytosis through coated pits. Almost 50 percent of the total pool of alpha-adaptins was coimmunoprecipitated with the EGF receptor when A-431 cells were treated with EGF at 37 degrees C, but not at 4 degrees C. Partial proteolysis of alpha-adaptin suggested that the amino-terminal domain is the region that associates with the EGF receptor. The extent of receptor-adaptin association was increased in cells depleted of potassium to block endocytosis. These data suggest that receptor-adaptin association occurs in intact cells before coated pits are fully assembled.

Endocytosis of growth factor receptors

Binding of a growth factor (GF) to its specific receptor on the cell surface causes the initiation of a signal transduction cascade which eventually results in mitosis. GF:receptor complexes are removed from the cell surface via receptor-mediated endocytosis, a process which involves clathrin-coated pits. After internalization into the endosomal compartment, a significant pool of GFs and GF receptors escape recycling to the cell surface and are sorted to the degradation pathway. The ligand-induced internalization and lysosomal degradation of GF receptors result in the dramatic loss of surface receptors, a phenomenon termed receptor down-regulation. In this review, we discuss relevant biochemical, morphological and kinetic studies of the mechanism of GF endocytosis, and the possible role of this process in mitogenic signaling by growth factor receptors.

Analysis of the influences of the E5 transforming protein on kinetic parameters of epidermal growth factor binding and metabolism

The E5 protein of the bovine papillomavirus induces cellular transformation when transfected into NIH 3T3 cells, and the extent of focal transformation is enhanced by cotransfection with the epidermal growth factor (EGF) receptor (Martin et al., Cell 59:21-32, 1989). To determine whether E5 affects EGF:receptor interactions we analyzed the kinetics of 125I-EGF processing using a mathematical model that enabled us to evaluate rate constants for ligand association (ka), dissociation (kd), internalization (ke), recycling (kr), and degradation (kh). These rate constants were measured in NIH 3T3 cells transfected with the human EGF receptor (ER cells) and in cells transfected with both the EGF receptor and E5 (E5/ER cells). We found that the rate constant for 125I-EGF association ka was significantly decreased in E5/ER cells, but was apparently occupancy-independent in both cell lines. The 125I-EGF dissociation rate constant kd was significantly lower in E5 transformed cells, and increased with occupancy in both cell lines. This suggests that E5 alters the receptor before or during EGF binding so that ligand association is slower; however, once complexes are formed, EGF is bound more tightly to the receptor. Rate constants for internalization ke were also found to be occupancy-dependent, although at a given level of occupancy ke was similar for both cell lines. Also, there was no apparent effect of E5 on the recycling rate constant kr. The 125I-EGF degradation rate constant kh was 30% lower in E5 transformed cells, and was occupancy-independent. The overall effect of E5 is to stabilize intact EGF:receptor complexes which may alter mitogenic signaling of the receptor.

Multiple autophosphorylation sites of the epidermal growth factor receptor are essential for receptor kinase activity and internalization. Contrasting significance of tyrosine 992 in the native and truncated receptors

The role of epidermal growth factor (EGF) receptor autophosphorylation sites in the regulation of receptor functions has been studied using cells transfected with mutant EGF receptors. Simultaneous point mutation of 4 tyrosines (Y1068, Y1086, Y1148, Y1173) to phenylalanine, as well as removal of these sites by truncation of the carboxyl-terminal 123 amino acid residues, resulted in reduced receptor phosphorylation of an in vivo specific substrate phospholipase C-gamma 1 to less than 50% compared to the wild-type receptor. The internalization rate constant Ke was also significantly lower in these mutants (0.15/min) compared to cells transfected with wild-type receptor (0.27/min). Additional mutation of tyrosine 992 to phenylalanine in the truncated receptor mutant (Dc-123F) further decreased the receptor internalization rate to a minimal level (ke = 0.07-0.10/min), equivalent to the ke measured for cells expressing kinase-negative receptor (A721). Moreover, tyrosine kinase activity of the Dc-123F receptor toward phospholipase C-gamma 1, compared to wild-type receptor, was reduced by 90%. Taken together, these results show that EGF receptor lacking five autophosphorylation sites functions similar to a kinase-negative receptor. Mutation of tyrosine residue Y992 alone in the context of full length EGF receptor, however, did not affect receptor internalization or kinase activity toward phospholipase C-gamma 1. These data indicate that tyrosine 992 is critical for substrate phosphorylation and internalization only in the context of the truncated receptor, and that minor autophosphorylation sites, such as Y992, may act as compensatory regulatory sties in the absence of the major EGF receptor autophosphorylation sites.