The validation of a new vascular damage assay for photodynamic therapy agents

The therapeutic effect of photodynamic therapy (PDT: photodynamic sensitizer + light) is partly due to vascular damage. This report describes a new vascular photodamage assay for PDT agents and a validation of the assay. The method described here quantitates changes in tissue blood perfusion based on the relative amount of injected fluorescein dye in treated and untreated tissues. A specially designed fluorometer uses chopped monochromatic light from an argon laser as a source for exciting fluorescein fluorescence. The fluorescent light emitted from the tissue is collected by a six element fiberoptic array, filtered and delivered to a photodiode detector coupled to a phase-locked amplifier for conversion to a voltage signal for recording. This arrangement permits a rather simple, inexpensive construction and allows for the simultaneous use of the argon laser by other investigators. The routine assay for characterizing a specific photosensitizer at a standard dose consists of the sequential allocation of eight mice to a set of different light doses designed to span the dose-response range of fluorescein fluorescence exclusion (measured 8-10 min after fluorescein injection). The assay validation experiment used an anionic photosensitizer, 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a at a dose of 0.4 mumol/kg. The parameter estimates (n = 34 mice) from fitting the standard Hill dose-response model to the data were: median fluorescence exclusion light dose FE50 = 275 +/- 8.3 J/cm2 and Hill sigmoidicity parameter m = -3.66 +/- 0.28. Subsets of the full data set randomly selected to simulate a standard eight mice experiment yielded similar parameter estimates. The new assay provides reliable estimates of PDT vascular damage with a frugal sequential experimental design.

A retrospective study of the use of cisplatinum-5-fluorouracil neoadjuvant chemotherapy in cervical-node-positive nasopharyngeal carcinoma (NPC)

A retrospective study on 422 nasopharyngeal carcinoma (NPC) patients with cervical nodal metastases treated between 1984 and 1987 was performed. 169 received neoadjuvant chemotherapy (CHEMO) with cisplatinum and 5-fluorouracil for two or three courses prior to definitive radiotherapy and 253 were treated by radical radiotherapy alone (NCHEMO). While the primary tumour (T-stage) prognosticators had been comparable between the two groups, CHEMO had significantly more advanced cervical nodal metastases with bulkier nodes and more low-cervical and supraclavicular nodes (P < 0.05) which could account for its overall worse survival, poorer regional tumour control and a trend towards worse systemic tumour control. The worse regional control in CHEMO for Ho's N1 could be the result of more bulky nodes and more tumours infiltrating the skull base and/or causing cranial nerve(s) palsy. There was no statistical or apparent difference between CHEMO and NCHEMO for the same Ho's overall stages of NPC with comparable nodal and primary tumour characteristics for the clinical endpoints of actuarial survival rate (ASR), disease-free survival rate (DFS), free of local failure survival rate (FLF), and free from distant metastases survival rate (FDM), despite the presence of significantly more fixed nodes and bulky nodes. This suggests a possible beneficial effect of the neoadjuvant chemotherapy. However, multivariate analysis has not shown the administration of the neoadjuvant chemotherapy to be of prognostic significance. Even though the chemotherapy was well tolerated with little toxicity, we recommend against the routine use of neoadjuvant chemotherapy in cervical-node-positive NPC outside the context of a prospective randomised clinical trial.

Lactose fed-batch overexpression of recombinant metalloproteins in Escherichia coli BL21 (DE3): process control yielding high levels of metal-incorporated, soluble protein

A method for producing recombinant proteins in pilot scale fermentation equipment using a glucose fed-batch initial growth, followed by a midlog phase feeding of a glucose and lactose mixture is described. Using the host strain Escherichia coli BL21(DE3), the diiron protein stearoyl-acyl carrier protein delta 9 desaturase has been overexpressed at a biomass level of up to 12 g x liter-1 dry cell weight, representing a 12-fold increase in volumetric productivity relative to that obtained from batch fermentations. Under these conditions, a maximum of 36% of the total cellular protein accumulates as the desaturase polypeptide. A correlation between the slowed growth rate of the fed-batch culture, a continued, albeit slower, exponential growth under inducing conditions, and a favorable partitioning between formation of the soluble holoprotein and inclusion bodies is reported. This correlation suggests that fed-batch techniques can be used to beneficially influence rate-limiting processes in the maturation of overexpressed proteins, such as metal uptake and incorporation proposed here. By using cells produced from the fed-batch method, the iron-containing, soluble desaturase can be purified in a yield of up to 66 mg x g-1 dry cell weight (approximately 500 mg x liter-1 culture), representing a three to fivefold increase in the yield relative to that obtained from batch fermentations. In addition, these methods are suitable for the production of the Anabena 7120 vegetative [2Fe 2S] ferredoxin in E. coli BL21(DE3) pLysS, a host strain used for the overexpression of toxic proteins.

Association of 75/80-kDa phosphoproteins and the tyrosine kinases Lyn, Fyn, and Lck with the B cell molecule CD20. Evidence against involvement of the cytoplasmic regions of CD20

CD20, a non-glycosylated cell-surface protein expressed exclusively on B lymphocytes, is one of a family of 4-pass transmembrane molecules that also includes the beta chain of the high affinity receptor for IgE. The precise function of CD20 is unknown, although in vitro effects of CD20-specific antibodies on resting B cells indicate that it is able to transduce an extracellular signal affecting the G0/G1 cell cycle transition. Previous studies have demonstrated that CD20-initiated intracellular signals involve tyrosine kinase activation and that CD20 is tightly associated with both serine and tyrosine kinases. Here, analysis of CD20-associated molecules has revealed that CD20 is associated with the Src family tyrosine kinases p56/53lyn, p56lck, and p59fyn and with 75/80-kDa proteins phosphorylated in vivo on tyrosine residues. Mutagenesis of CD20 was performed to define regions of CD20 involved in intermolecular interactions. Mutants were analyzed in the human T lymphoblastoid cell line Molt-4, in which ectopically expressed wild-type CD20 associated with p59fyn, p56lck, and 75/80-kDa phosphoproteins. Deletion of major portions of the cytoplasmic regions of CD20 did not abolish its association with either p75/80 or tyrosine kinases. The interaction between CD20 and the Src-related kinases is therefore likely to be independent of CD20 cytoplasmic domains and may occur indirectly. The interaction may be mediated by the p75/80 phosphoproteins, which were found to be tightly associated with the Src family kinases isolated from the CD20 complex.

Characterization of the interaction between CD45 and CD45-AP

CD45, a leukocyte-specific transmembrane protein tyrosine phosphatase, is required for critical signal transduction pathways in immune responses. To elucidate the molecular interactions of CD45 with other proteins involved in CD45-mediated signal transduction pathways, we have recently cloned a 30-kDa phosphorylated protein, CD45-AP, which specifically associates with CD45. Binding analysis employing several deleted or chimeric forms of CD45-AP and CD45 demonstrated that the potential transmembrane segment of CD45-AP bound to the transmembrane portion of CD45. CD45-AP was found in particulate fractions of lymphocytes along with CD45, indicating that it is likely to be a transmembrane protein. In addition, CD45-AP was resistant to proteolysis by tosylphenylalanyl chloromethyl ketone-treated trypsin applied to intact cells. This is consistent with the most likely membrane orientation of CD45-AP predicted from the amino acid sequence, that is, only a short amino-terminal segment of CD45-AP is extracellular. We propose that CD45-AP interacts with CD45 at the plasma membrane and that the bulk of CD45-AP located in the cytoplasm act as an adapter which directs the interaction between CD45 and other molecules involved in CD45-mediated signal transduction pathways.

Antioxidant enzyme activities and lipid peroxidation levels in exercised and hypertensive rat tissues

Previous studies have shown that exercise-induced changes in muscle antioxidant status occur shortly after exercise. The present studies were designed to determine if longer-term exercise-related changes in antioxidant enzyme activities in both normotensive (WKY) and hypertensive rats (SHR) occurred, and if these changes were related to the levels of lipid peroxidation. WKY and SHR rats were exercised over a 10-week period using a progressive treadmill regimen. After a 1-week detraining period, the animals were euthanized and measurements of tissue antioxidant enzyme activities and lipid peroxide levels were determined in both exercised and cage-sedentary groups. Decreases in antioxidant activities (particularly glutathione peroxidase and catalase) in liver, kidney, skeletal and cardiac were associated with exercise training in both WKy and SHR rats (e.g. left ventricular glutathione peroxidase specific activity in WKY rats was decreased from 234 +/- 25 [SD, n = 12] to 187 +/- 17 [SD, n = 11] units/mg protein). Elevations in activities of antioxidant enzymes were generally associated with hypertension in these tissues (e.g. left ventricular glutathione peroxidase specific activity in SHR rats was 275 +/- 30 [SD, n = 12] units/mg protein), but changes in activities were more variable than those seen in response to exercise. Exercise-related changes in tissue levels of thiobarbituric acid-reactive substances (an indirect measure of tissue lipid peroxide levels) generally did not correlate with exercise-related antioxidant enzyme activity changes, and hypertension had no effect on these levels except in liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Environmental effects on thermoregulation and breathing patterns during early postnatal development in hand-reared lambs

This study examines the effect of hand-rearing developing lambs in a warm (WR; 25 degrees C) or cool (CR; 10-15 degrees C) ambient temperature on the control of thermoregulation and breathing patterns, when maintained at a fixed level of nutrition over the first month of postnatal life. Measurements were made during non-rapid eye movement sleep whilst lambs were maintained for at least 1 h at warm (28-19 degrees C) and cold (14-5 degrees C) ambient temperatures at 1, 7, 14 and 30 days of age. All lambs were able to maintain normal body temperature, but oxygen consumption was higher in CR lambs at 14 and 30 days of age. At 1 day of age shivering was rarely observed in any lambs, but at 7 and 14 days of age more WR than CR lambs responded to cold exposure via shivering. Plasma concentrations of triiodothyronine were higher at 7 and 14 days of age in CR lambs. Breathing frequencies were similar in WR and CR lambs, and from 7 days of age the incidence of expiratory laryngeal braking was higher in warm compared with cold study temperatures. By 30 days of age the recruitment of this mechanism was greater in CR lambs. Mean growth rate was slower over the first week of postnatal life in CR compared with WR lambs. This difference decreased over the first month of life, as growth rate increased from 83 to 130 g day-1 in the CR group but remained constant at approximately 150 g day-1 in the WR lambs. Total weight of the lungs and heart, but not the liver, were lower at 1 month but not at 1 week of postnatal life in CR lambs. It is concluded that a modest decrease in the ambient temperature in which postnatal lambs are reared, when on a fixed feed intake, alters lung size, the recruitment of laryngeal braking and the control of body temperature.

Interferon-alpha and survival in renal cell cancer

OBJECTIVE

To establish whether the use of interferon-alpha might result in improved survival, using two large series of patients with advanced renal cell cancer treated during studies of chemotherapy and biological therapy, respectively.

PATIENTS AND METHODS

Patients treated either in the Eastern Cooperative Oncology Group (ECOG) chemotherapy protocols (327 patients) or in protocols employing interferon as part of a European randomized study or phase II studies at the Norwegian Radium Hospital (231 patients) were retrospectively analysed. Groups for comparison were matched by exclusion of those with an ECOG performance status > 2, no prior nephrectomy, brain metastases or prior chemotherapy. Univariate analysis of prognostic factors for survival was performed by the log rank method and multivariate analysis by Cox regression.

RESULTS

Univariate analysis of the whole population showed that performance status, time from diagnosis to treatment, sites of metastases and the use of interferon carried the greatest prognostic significance. In multivariate analysis, the use of interferon remained a significant predictor of survival (P < 0.001). Subgroup analysis suggested that the impact of interferon treatment was greatest in those patients with two of the following characteristics: good performance status, an interval of > 2 years from diagnosis to treatment and no more than one site of metastasis.

CONCLUSION

Although a prospective randomized trial is needed to establish definite benefit from the use of interferon in advanced renal cell cancer, this analysis supports the rationale for performing such a trial, particularly in patients with relatively good prognostic features. Patients should be entered into the Medical Research Council study comparing interferon with medroxyprogesterone acetate.

Complications after radiotherapy and radical hysterectomy in early-stage cervical carcinoma

OBJECTIVE

To evaluate the overall complications, major as well as minor, in patients treated for early-stage cervical carcinoma as related to treatment parameters.

METHODS

In this retrospective study, 167 consecutive patients with early-stage cervical carcinoma treated with preoperative radiotherapy and radical hysterectomy were investigated. Clinical data were collected from the medical files.

RESULTS

Transient or permanent complications appeared in up to half of all patients. Seven percent exhibited intraoperative complications and 35% suffered from early postoperative urinary tract problems; most frequently urinary tract infection. After one year, the urinary tract complications dominated; voidance difficulties and incontinence being most common. Gastrointestinal complications occurred in 15% of patients. Lymphedema appeared during the first year in 21% of the patients but several of the mild or moderate cases improved after the first year. The relative risk of lymphedema was increased with shorter duration of surgery, extensive preoperative irradiation to the bladder and after external postoperative irradiation. Some form of late sequelae remained in every fifth patient, and every fourth patient, aged 24-44 years, periodically suffered from vasomotor symptoms despite estrogen replacement therapy.

CONCLUSION

The complications after radiotherapy and radical hysterectomy in early stage cervical carcinoma suggest that attempts should be made to evaluate effective treatments designed to minimize risk to the patients.

Quality of life assessment in gynaecological cancer patients

The feasibility of quality of life (QOL) assessment in a heterogeneous group of gynaecological cancer patients undergoing chemotherapy was determined. All new patients being prescribed cytotoxic chemotherapy were asked to complete a modified QOL assessment tool. The elected assessment tool is the Functional Assessment Cancer Therapy-General (FACT-G) tool, comprising 33 questions under 5 broad categories: physical well-being, social well-being, relationship with doctor, emotional well-being and functional well-being. Raw scores were calculated and then transformed to a 0-100 scale. Twenty eight patients received a total of 75 treatment cycles of chemotherapy. Four patients were not offered the assessment due to language difficulties. All patients offered the test satisfactorily completed the test to allow statistical analysis. The average number of chemotherapy courses received was 2.5 (range: 1-6). Of a total possible 2,475 study items (33 items x 75 cycles), 240 items were not answered (10%). Of these 240 unanswered items, 2 items (#14 and #15) comprised 38%. The mean transformed score for physical well-being was 32 (SE 2.5), for social well-being the mean transformed score was 50 (SE 1.7), relationship with doctor 86 (SE 2.4), emotional well-being 41 (SE 2) and functional well-being was 54 (SE 2.6). The assessment of QOL indices in gynaecological cancer patients undergoing chemotherapy is feasible. Further research needs to determine the optimal QOL tool for this patient population.

Substrate-based inhibitors of lanosterol 14 alpha-methyl demethylase: II. Time-dependent enzyme inactivation by selected oxylanosterol analogs

Selected 15-, 32-, and 15,32-substituted lanosterol analogs are shown here to display time-dependent inactivation and lanosterol 14 alpha-methyl demethylase. These molecules are competitive with respect to substrate and require NADPH and O2 in order to display time dependence, thus supporting the premise that they are mechanism-based inactivators. Structural features required for lanosterol demethylation by the lanosterol demethylase such as nuclear double bond location and availability of an abstractable 15 alpha-proton are also essential elements for time-dependent inactivation. 32-(S)-Vinyllanost-8-en-3 beta,32-diol is a potent time-dependent inactivator (Kinact/Ki = 0.36 min-1 microM-1), while the 32-(R)-vinyllanost-8-en-3 beta,32-diol functions solely as a competitive demethylase inhibitor. These results support the premise that stereoselective oxidation occurs during lanosterol demethylation and that the 32-pro-S proton is abstracted during the demethylation reaction.

When patients and pediatricians say good-bye in a pediatric resident continuity clinic

Pediatric residency programs require a 3-year continuity clinic experience for residents. To our knowledge, no authors have examined the impact of termination at the end of the residency among the child, parent, and pediatrician. This article discusses an exploration that evolved in response to the questions that third-year pediatric residents asked concerning how to say good-bye to their primary care patients in the context of their continuity clinic. The first panel addressed parental and patient issues, and the second addressed the impact on the pediatrician. The parents on the panel stated that it was important that they be notified in advance of their pediatrician's departure, that they believed they had played an important role in the resident's education, and that they wanted a voice in the selection of their child's future pediatrician. The pediatricians on the panel all felt sadness, relief, and guilt as a result of the termination, but guilt that the family would feel abandoned was the strongest emotion. Few pediatricians on the panel acknowledged the impact of the relationship on themselves and the importance of including the parents in the decision to choose the child's future pediatrician. The issue of termination needs more deliberate attention in pediatric training programs. A structured system for teaching residents to manage the termination process is proposed.

Dopamine D2 receptor gene (DRD2) haplotypes and the defense style questionnaire in substance abuse, Tourette syndrome, and controls

The defence style questionnaire (DSQ) was administered to Caucasian males consisting of 123 subjects from a V.A. addiction treatment unit (ATU), 42 Tourette syndrome (TS) subjects, and 49 controls. For the ATU and TS subjects, there was a significant decrease in the mean score for mature defenses and a significant increase in mean score for immature defenses compared to controls. Many of the individual subscores showed the same significant differences. Dopamine D2 receptor (DRD2) gene haplotypes, identified by allele specific polymerase chain reaction of two mutations (G/T and C/T) 241 base pairs apart, were determined in 57 of the ATU subjects and 42 of the controls. Subjects with the 1 haplotype tended to show a decrease in mature and an increase in neurotic and immature defense styles compared to those without the 1 haplotype. Of the eight times that the subscale scores were significant for haplotype 1 versus non-1, they were always in this direction. There results suggest that the DRD2 locus is one factors controlling defense styles. The difference in the mean scores between controls and substance abuse subjects indicates that other genes and environmental factors also play a role.

Where there is no family doctor: the development of family practice around the world

Family physicians are generalists trained at the postgraduate level to address the majority of primary care needs of patients of all ages in communities they serve. Throughout the world there is a need for family physicians to serve as cornerstones of comprehensive health care systems that provide high-quality, cost-effective medical and public health services to the entire population. To meet this need, each country must value and adequately finance essential medical and public health services and must provide family physicians with a thorough education focused on the relevant health care problems of the population being served. The authors present an overview of the status of this training throughout the world, outline challenges to the development of such training, and suggest strategies for successful development accompanied by illustrative case studies from South Korea, Venezuela, and Pakistan.

Potential dangers of oxygen supplementation during facial surgery

The use of local anesthesia and intravenous sedation has made same-day outpatient surgery a viable option for many aesthetic and reconstructive procedures. These procedures often include the use of supplemental oxygen. Oxygen-enriched environments increase the combustibility of most materials, and "oxygen pooling" has been suspected to play an integral role in intraoperative fires. A personal experience with an intraoperative explosion and fire during a cosmetic blepharoplasty compelled us to explore the potential danger inherent in the use of supplemental oxygen as well as potential strategies to minimize that danger. This study systematically examines the microenvironment created by the use of oxygen both in the operative field and beneath the surgical drapes under conditions simulating routine facial surgery and various recommended modifications of its delivery. With the use of oxygen supplementation, oxygen concentration beneath the drapes was found to be consistently elevated when compared with ambient air (20.9 percent) and reached levels as high as 53.5 percent. Oxygen concentration in the operative environment was mildly but not significantly elevated. Although criteria for the use of oxygen supplementation are not clear, when administration is deemed necessary, the use of a posterior pharyngeal catheter for its delivery had no advantage over nasal prongs. However, appropriate alternatives include the use of "open face" draping techniques, the use of compressed air beneath the drapes as a substitute for oxygen supplementation in unsedated patients, and cessation of oxygen supplementation for 60 seconds prior to the use of a possible ignition source with oxygen flow rates of less than 3 liters per minute.

Treatment of cervical-carcinoma by wertheim-meigs surgery - long-term follow-up results in a well-defined Swedish region

In a retrospective analysis of a complete geographic series of cervical carcinomas treated by Wertheim-Meigs radical surgery, a number of important prognostic factors were evaluated and long-term survival data are presented. In all, 367 women with FIGO stage I-II tumors were included. The main histopathologic types were squamous cell carcinoma in 84% and adenocarcinoma in 12%. The mean age of the patients was 42.5 (range 19-68) years. In 125 women (34%), adjuvant radiotherapy was administered pre- or postoperatively. The median period of follow-up was 12 (range 2-27) years. In 88% of the specimens surgery (93% in stage I and 66% in stage II) was classified as radical with regard to the excision margins. This was an important and highly significant prognostic factor. If the margins were wide and free of tumor, the 10-year survival rate was 93%, but if margins were infiltrated by the tumor, the survival rate was 14%. Pelvic lymph node involvement was recorded in 52 cases (14%). The frequency of lymph node spread was associated with tumor stage (IA O%, IB 14%, IIA 32%). The probability of survival of the complete series was 93% at 5 years and 84% at 10 years. In cases of lymph node involvement, the 10-year survival rate was 57%. The preoperative tumor stage had a highly significant influence on long-term tumor-specific survival. Tumor grade was also a significant prognostic factor, but not the histologic type (squamous, adenosquamous, or adenocarcinoma). Age and parity were also insignificant prognostic factors. The tumor recurred in 59 cases (16%). The mean time to relapse was 28 months. The 10-year survival was 29% for this group of patients. Peroperative complications were recorded in 50 patients (14%). Excessive bleeding (11%) and urinary tract injuries (3%) were most frequent. Postoperatively, 101 patients (28%) had some kind of complication associated with the surgical procedure. Surgical complications were more frequent among women over 50 years of age. Bladder dysfunction (11%) and obstruction of the ureter (8%) were recorded most frequently. In 19 cases (5.2%), urinary tract or intestinal fistulas were diagnosed during the period of follow-up. With increasing experience of the surgeons and fewer stage II tumors, the frequency of fistulas associated with the surgical procedure decreased to 2.4% during the latter part (1975-90) of the period. Adjunctive postoperative radiotherapy increased the risk of late complications. In 8 cases (6.4%), serious complications associated with the combination of surgery and radiotherapy were reported.

Topical fibronectin ophthalmic solution in the treatment of persistent defects of the corneal epithelium. Chiron Vision Fibronectin Study Group

PURPOSE

We sought to evaluate the efficacy of topical fibronectin ophthalmic solution, containing 3.5 mg/ml of human fibronectin, in the treatment of persistent epithelial defects of the cornea.

METHODS

In a double-masked, randomized clinical trial, patients with a persistent, corneal epithelial defect of at least 14 days in duration, and at least 2 mm in width along the larger axis, were sought from the practices of 38 clinical investigators. After a 14-day washout period, 65 patients were randomly assigned to one of three treatment groups. One group (n = 20) received fibronectin drops; the second (n = 23) received drops of the vehicle from the fibronectin solution; and the third (n = 22) received a placebo.

RESULTS

After 21 days of treatment, there was no difference in percentage reduction of the corneal epithelial defect size; the average percentage of reduction of defect area ranged from 46.5% to 54.3%. Fibronectin treatment showed a beneficial effect for patients with larger baseline defects (10 mm2 or greater in area); however, no such effect was observed among patients with smaller defects. Defect duration before treatment had a significant effect on outcome (P = .007); defects of longer duration were less likely to decrease in size over the course of the study.

CONCLUSIONS

All three treatment groups showed similar reductions in defect size; therefore, this study provides no support for the efficacy of fibronectin treatment of persistent, corneal epithelial defects. Defect duration showed a negative association with reduction in defect size. Because strict control of topical applications during the washout and treatment periods resulted in beneficial responses, physicians should carefully consider the topical medications used by patients who have persistent, corneal epithelial defects.

Non-radioactive method to measure CD45 protein tyrosine phosphatase activity isolated directly from cells

Preparation of radioactive phosphorylated substrates is laborious, yields a limited amount of substrate with a short half-life and generates a low percentage of phosphorylated product which then has to be separated from non-phosphorylated material. These factors limit the usefulness of radioactive phosphorylated substrates in phosphatase assays and prohibit their use for kinetic analysis, which often requires large amounts of substrate. An alternative method for the kinetic analysis of purified or recombinant soluble phosphatases uses the malachite green reagent which can detect nanomoles of phosphate released from chemically synthesized phosphorylated peptides. In this report we describe a rapid and sensitive non-radioactive method that can be used to measure protein tyrosine phosphatase (PTP) activities of both transmembrane and soluble phosphatases immunoprecipitated directly from cells. This colorimetric microassay is performed in 96 well microtitre plates and can reliably detect 100 pmol of free phosphate released, using a standard microplate reader. The phosphatase activity of CD45, a transmembrane PTP, was determined from as few as 1 x 10(4) lymphoid cells. The development of this colorimetric assay to measure immunoprecipitated CD45 PTP activity isolated from very small numbers of cells has general applicability for other PTPs and will help identify the cellular situations and conditions that result in changes in PTP activity.