POS1132 PATTERNS OF JOINT SURGERY IN THE TEN YEARS PRIOR TO PRIMARY KNEE REPLACEMENT IN ENGLAND AND SWEDEN – A POPULATION-BASED CASE-CONTROL STUDY

Background

Primary knee replacement (KR) is an effective intervention for end-stage knee osteoarthritis (OA). However, there are no definitive recommendations for the timing at which patients should receive this surgery, potentially resulting in differences in referral patterns depending on geographical area or the clinicians‘ preferences.

Objectives

To investigate the prevalence of meniscus, knee ligament and knee synovial surgeries as well as knee osteotomy and hip replacement (HR) across the ten years preceding a KR in cases and controls in England and Sweden.

Methods

This was a multi-national, population-based, case-control study within England and Sweden. Cases underwent primary TKR and controls, matched using risk-set sampling by age, sex and practice/region, did not. Electronic healthcare databases were used; the Clinical Practice Research Datalink (CPRD) in England, and the Health Register of Skåne (Sweden’s southernmost region) in Sweden.

ICD-10 codes and KVÅ codes in Sweden and Medcodes (SNOMED CT (UK edition) and Read codes) in England were used to identify subjects aged ≥45 years who underwent primary KR between 1st January 2015 and 31st December 2019. Eligible cases had to be registered for ≥10 years prior to the primary KR (index date), and have no record of prior KR in that period.

Office of Population Censuses and Surveys (OPCS) codes in England and ICD-10 codes in Sweden were used to identify selected orthopaedic surgeries.

Meniscal (e.g. excision, resection, repair) and ligament surgery (e.g. ligament reconstruction, replacement, suture) were included, as well as osteotomy (e.g. angle, rotational or displacement osteotomy of the knee or lower leg). Hip replacement (HR) (any primary HR) was also included, to evaluate the rate at which patients undergoing KR also undergo further major arthroplasty in the years preceding this – The annual prevalence of having at least one recorded surgery for each type in each of the 10 years preceding KR was estimated using Poisson regression models and expressed per 1,000 people.

Results

We identified 6,337 and 47,010 subjects who underwent a knee replacement between 2015 and 2019 in southern Sweden and England, respectively (Table 1). Overall, the prevalence of all analysed surgeries was consistently lower in the controls with minimal trends detectable throughout follow-up in both England and Sweden (Figure 1).

Table 1.

demographic

SwedenEnglandCases(n=6,337)Controls(n=6,337)Cases(n=47,010)Controls(n=47,010)Age, mean (SD)69.0 (8.9)68.9 (9.1)69.6 (9.6)69.6 (9.6)Female Sex, n (%)3,585 (56.6%)3,585 (56.6%)26,154 (55.6%)26,154 (55.6%)Surgeries, n Hip replacement5623243,9331,889 Meniscus384448,659833 Ligaments1659011 Synovial1641536930 Osteotomy9831075

On the other hand, an increasing trend among the cases, signifying a higher prevalence of surgeries when nearing KR, was observed for HR and meniscal surgeries in both nations. The prevalence of HR was similar in England and southern Sweden at all-time points showing an increase most noticeable in the 3 years before KR. The prevalence of meniscus surgery in England was higher than the one observed in Sweden throughout the follow-up. Prevalence in England increased most noticeably in the four years prior to KR reaching 33.2 (95%CI 31.6, 34.9) surgeries per 1,000 people in the year preceding KR. In Sweden, the prevalence of meniscus surgery remained between four and eight surgeries per 1,000 people until the last year prior to KR when the prevalence increased to 13.8 (95%CI 11.9, 16.2) surgeries per 1,000 people.

Conclusion

HR and meniscal surgeries are common procedures that a person is likely to have experienced in the ten years prior to a KR. Comparing England and southern Sweden, we noticed similar prevalence and trends for what concerns HR suggesting similar practice in the two healthcare systems. Meniscus surgeries were more frequently utilised in England. Nevertheless, in both countries, a marked increase in the prevalence of this surgery was observed in the last years prior to the KR.

Disclosure of Interests

None declared

Opioid use prior to total knee replacement: comparative analysis of trends in England and Sweden

OBJECTIVES

To describe and compare trends in the frequency of opioid prescribing/dispensing in English and Swedish patients with osteoarthritis prior to total knee replacement (TKR).

METHODS

49,043 patients from an English national database (Clinical Practice Research Datalink) and 5,955 patients from the Swedish Skåne Healthcare register undergoing TKR between 2015 and 2019 were included, alongside 1:1 age-, sex-, and practice (residential area) matched controls. Annual prevalence and prevalence rates ratio (PRR) of opioid prescribing/dispensing (any, by strength) in the 10 years prior to TKR (or matched index date for controls) were estimated using Poisson regression.

RESULTS

In England and Sweden, the prevalence of patients with osteoarthritis receiving any opioid prior to TKR increased towards the date of surgery from 24% to 44% in England and from 16% to 33% in Sweden. Prescribing in controls was stable, resulting in an increasing PRR (1.6-2.7) between 10 and 1 years prior to index date in both countries. No relevant cohort or period effect was observed in either country. Prevalence of opioid prescribing was higher in English cases and controls; weaker opioids were more commonly prescribed in England, stronger opioids in Sweden.

CONCLUSIONS

Temporal prevalence patterns of opioid prescribing between cases and controls are similar in England and Sweden. Opioids are still commonly used in TKR cases in both countries highlighting the lack of valid alternatives for OA pain management.

Important research outcomes for treatment studies of perinatal depression: systematic overview and development of a core outcome set

OBJECTIVE

To develop a Core Outcome Set (COS) for treatment of perinatal depression.

DESIGN

Systematic overview of outcomes reported in the literature and consensus development study.

SETTING

International.

POPULATION

Two hundred and twenty-two participants, mainly patients, healthcare professionals and researchers, representing 13 countries.

METHODS

A systematic overview of outcomes reported in recently published research, a two-round Delphi survey and a consensus meeting at which the final COS was decided using modified nominal group technique.

MAIN RESULTS

In the literature search, 1772 abstracts were identified and evaluated, and 165 studies were finally included in the review. In all, 106 outcomes were identified and included in the Delphi survey. In all, 222 participants registered for the first round of the Delphi survey and 151 (68%) responded. In the second round, 123 (55%) participants responded. Thirteen participants attended the consensus meeting, where the following nine outcomes were agreed upon for inclusion in the final COS: self-assessed symptoms of depression, diagnosis of depression by a clinician, parent to infant bonding, self-assessed symptoms of anxiety, quality of life, satisfaction with intervention, suicidal thoughts, attempted or committed suicide, thoughts of harming the baby, and adverse events.

CONCLUSIONS

The relevant stakeholders prioritised outcomes and reached consensus on a COS comprising nine outcomes. We expect that this COS will contribute to the consistency and uniformity of outcome selection and reporting in future clinical trials involving treatment of perinatal depression.

TWEETABLE ABSTRACT

Development of a core outcome set regarding treatment for perinatal depression by @SBU_en. TWEETABLE ABSTRACT.

Imatinib increases oxygen delivery in extracellular matrix-rich but not in matrix-poor experimental carcinoma

BACKGROUND

Imatinib causes increased turnover of stromal collagen, reduces collagen fibril diameter, enhances extracellular fluid turnover and lowers interstitial fluid pressure (IFP) in the human colonic carcinoma KAT-4/HT-29 (KAT-4) xenograft model.

METHODS

We compared the effects of imatinib on oxygen levels, vascular morphology and IFP in three experimental tumor models differing in their content of a collagenous extracellular matrix.

RESULTS

Neither the KAT4 and CT-26 colonic carcinoma models, nor B16BB melanoma expressed PDGF β-receptors in the malignant cells. KAT-4 tumors exhibited a well-developed ECM in contrast to the other two model systems. The collagen content was substantially higher in KAT-4 than in CT-26, while collagen was not detectable in B16BB tumors. The pO₂ was on average 5.4, 13.9 and 19.3 mmHg in KAT-4, CT-26 and B16BB tumors, respectively. Treatment with imatinib resulted in similar pO₂-levels in all three tumor models but only in KAT-4 tumors did the increase reach statistical significance. It is likely that after imatinib treatment the increase in pO₂ in KAT-4 tumors is caused by increased blood flow due to reduced vascular resistance. This notion is supported by the significant reduction observed in IFP in KAT-4 tumors after imatinib treatment. Vessel area varied between 4.5 and 7% in the three tumor models and was not affected by imatinib treatment. Imatinib had no effect on the fraction of proliferating cells, whereas the fraction of apoptotic cells increased to a similar degree in all three tumor models.

CONCLUSION

Our data suggest that the effects of imatinib on pO₂-levels depend on a well-developed ECM and provide further support to the suggestion that imatinib acts by causing interstitial stroma cells to produce a less dense ECM, which would in turn allow for an increased blood flow. The potential of imatinib treatment to render solid tumors more accessible to conventional treatments would therefore depend on the degree of tumor desmoplasia.

Regulation of Platelet Derived Growth Factor Signaling by Leukocyte Common Antigen-related (LAR) Protein Tyrosine Phosphatase: A Quantitative Phosphoproteomics Study

Intracellular signaling pathways are reliant on protein phosphorylation events that are controlled by a balance of kinase and phosphatase activity. Although kinases have been extensively studied, the role of phosphatases in controlling specific cell signaling pathways has been less so. Leukocyte common antigen-related protein (LAR) is a member of the LAR subfamily of receptor-like protein tyrosine phosphatases (RPTPs). LAR is known to regulate the activity of a number of receptor tyrosine kinases, including platelet-derived growth factor receptor (PDGFR). To gain insight into the signaling pathways regulated by LAR, including those that are PDGF-dependent, we have carried out the first systematic analysis of LAR-regulated signal transduction using SILAC-based quantitative proteomic and phosphoproteomic techniques. We haveanalyzed differential phosphorylation between wild-type mouse embryo fibroblasts (MEFs) and MEFs in which the LAR cytoplasmic phosphatase domains had been deleted (LARΔP), and found a significant change in abundance of phosphorylation on 270 phosphosites from 205 proteins because of the absence of the phosphatase domains of LAR. Further investigation of specific LAR-dependent phosphorylation sites and enriched biological processes reveal that LAR phosphatase activity impacts on a variety of cellular processes, most notably regulation of the actin cytoskeleton. Analysis of putative upstream kinases that may play an intermediary role between LAR and the identified LAR-dependent phosphorylation events has revealed a role for LAR in regulating mTOR and JNK signaling.

Multiple routes of endocytic internalization of PDGFRβ contribute to PDGF-induced STAT3 signaling

Platelet-derived growth factor receptor β (PDGFRβ) is a receptor tyrosine kinase which upon activation by PDGF-BB stimulates cell proliferation, migration and angiogenesis. Ligand binding induces intracellular signaling cascades but also internalization of the receptor, eventually resulting in its lysosomal degradation. However, endocytic trafficking of receptors often modulates their downstream signaling. We previously reported that internalization of PDGFRβ occurs via dynamin-dependent and -independent pathways but their further molecular determinants remained unknown. Here we show that in human fibroblasts expressing endogenous PDGFRβ and stimulated with 50 ng/ml PDGF-BB, ligand-receptor uptake proceeds via parallel routes of clathrin-mediated endocytosis (CME) and clathrin-independent endocytosis (CIE). CME involves the canonical AP2 complex as a clathrin adaptor, while CIE requires RhoA-ROCK, Cdc42 and galectin-3, the latter indicating lectin-mediated internalization via clathrin-independent carriers (CLICs). Although different uptake routes appear to be partly interdependent, they cannot fully substitute for each other. Strikingly, inhibition of any internalization mechanism impaired activation of STAT3 but not of other downstream effectors of PDGFRβ. Our data indicate that multiple routes of internalization of PDGFRβ contribute to a transcriptional and mitogenic response of cells to PDGF.

LAR protein tyrosine phosphatase regulates focal adhesions via CDK1

Focal adhesions are complex multi-molecular structures that link the actin cytoskeleton to the extracellular matrix via integrin adhesion receptors and play a key role in regulation of many cellular functions. LAR is a receptor protein tyrosine phosphatase that regulates PDGF signalling and localises to focal adhesions. We have observed that loss of LAR phosphatase activity in mouse embryonic fibroblasts results in reduced numbers of focal adhesions and decreased adhesion to fibronectin. To understand how LAR regulates cell adhesion we used phosphoproteomic data, comparing global phosphorylation events in wild type and LAR phosphatase-deficient cells, to analyse differential kinase activity. Kinase prediction analysis of LAR-regulated phosphosites identified a node of cytoskeleton- and adhesion-related proteins centred on cyclin-dependent kinase-1 (CDK1). We found that loss of LAR activity resulted in reduced activity of CDK1, and that CDK1 activity was required for LAR-mediated focal adhesion complex formation. We also established that LAR regulates CDK1 activity via c-Abl and PKB/Akt. In summary, we have identified a novel role for a receptor protein tyrosine phosphatase in regulating CDK1 activity and hence cell adhesion to the extracellular matrix.

VE-PTP regulates VEGFR2 activity in stalk cells to establish endothelial cell polarity and lumen formation

Vascular endothelial growth factor (VEGF) guides the path of new vessel sprouts by inducing VEGF receptor-2 activity in the sprout tip. In the stalk cells of the sprout, VEGF receptor-2 activity is downregulated. Here, we show that VEGF receptor-2 in stalk cells is dephosphorylated by the endothelium-specific vascular endothelial-phosphotyrosine phosphatase (VE-PTP). VE-PTP acts on VEGF receptor-2 located in endothelial junctions indirectly, via the Angiopoietin-1 receptor Tie2. VE-PTP inactivation in mouse embryoid bodies leads to excess VEGF receptor-2 activity in stalk cells, increased tyrosine phosphorylation of VE-cadherin and loss of cell polarity and lumen formation. Vessels in ve-ptp^−/− teratomas also show increased VEGF receptor-2 activity and loss of endothelial polarization. Moreover, the zebrafish VE-PTP orthologue ptp-rb is essential for polarization and lumen formation in intersomitic vessels. We conclude that the role of Tie2 in maintenance of vascular quiescence involves VE-PTP-dependent dephosphorylation of VEGF receptor-2, and that VEGF receptor-2 activity regulates VE-cadherin tyrosine phosphorylation, endothelial cell polarity and lumen formation.

Vascular endothelial growth factor is implicated in blood vessel development. In zebrafish, Hayashi et al. find that blood vessel development is dependent on the suppression of vascular endothelial growth factor by the phosphatase VE-PTP, which is recruited by activation of the angiopoietin receptor Tie2.

The Fer tyrosine kinase is important for platelet-derived growth factor-BB-induced signal transducer and activator of transcription 3 (STAT3) protein phosphorylation, colony formation in soft agar, and tumor growth in vivo

Fer is a cytoplasmic tyrosine kinase that is activated in response to platelet-derived growth factor (PDGF) stimulation. In the present report, we show that Fer associates with the activated PDGF β-receptor (PDGFRβ) through multiple autophosphorylation sites, i.e. Tyr-579, Tyr-581, Tyr-740, and Tyr-1021. Using low molecular weight inhibitors, we found that PDGF-BB-induced Fer activation is dependent on PDGFRβ kinase activity, but not on the enzymatic activity of Src or Jak kinases. In cells in which Fer was down-regulated using siRNA, PDGF-BB was unable to induce phosphorylation of STAT3, whereas phosphorylations of STAT5, ERK1/2, and Akt were unaffected. PDGF-BB-induced activation of STAT3 occurred also in cells expressing kinase-dead Fer, suggesting a kinase-independent adaptor role of Fer. Expression of Fer was dispensable for PDGF-BB-induced proliferation and migration but essential for colony formation in soft agar. Tumor growth in vivo was delayed in cells depleted of Fer expression. Our data suggest a critical role of Fer in PDGF-BB-induced STAT3 activation and cell transformation.

Dynamin inhibitors impair endocytosis and mitogenic signaling of PDGF

Platelet-derived growth factor (PDGF) isoforms regulate cell proliferation, migration and differentiation both in embryonic development and adult tissue remodeling. At the cellular level, growth-factor signaling is often modulated by endocytosis. Despite important functions of PDGF, its endocytosis remains poorly studied, mainly for lack of tools to track internalized ligand by microscopy. Here, we developed such a tool and quantitatively analyzed internalization and endosomal trafficking of PDGF-BB in human fibroblasts. We further show that PDGF can be internalized in the presence of dynamin inhibitors, arguing that both dynamin-dependent and dynamin-independent pathways can mediate PDGF uptake. Although these routes operate with somewhat different kinetics, they both ultimately lead to lysosomal degradation of PDGF. Although acute inhibition of dynamin activity only moderately affects PDGF endocytosis, it specifically decreases downstream signaling of PDGF via signal transducer and activator of transcription 3 (STAT3). This correlates with reduced expression of MYC and impaired cell entry into S-phase, indicating that dynamin activity is required for PDGF-induced mitogenesis. Our data support a general view that the components governing endocytic trafficking may selectively regulate certain signaling effectors activated by a growth factor.

Macropinocytosis of the PDGF β-receptor promotes fibroblast transformation by H-RasG12V

Fibroblast transformation by H-RasG12V induces internalization of PDGFRβ by macropinocytosis, enhancing its signaling activity and increasing anchorage-independent proliferation. It is proposed that H-Ras transformation promotes tumor progression by enhancing growth factor receptor signaling through increased receptor macropinocytosis.

Receptor tyrosine kinase (RTK) signaling is frequently increased in tumor cells, sometimes as a result of decreased receptor down-regulation. The extent to which the endocytic trafficking routes can contribute to such RTK hyperactivation is unclear. Here, we show for the first time that fibroblast transformation by H-RasG12V induces the internalization of platelet-derived growth factor β-receptor (PDGFRβ) by macropinocytosis, enhancing its signaling activity and increasing anchorage-independent proliferation. H-RasG12V transformation and PDGFRβ activation were synergistic in stimulating phosphatidylinositol (PI) 3-kinase activity, leading to receptor macropinocytosis. PDGFRβ macropinocytosis was both necessary and sufficient for enhanced receptor activation. Blocking macropinocytosis by inhibition of PI 3-kinase prevented the increase in receptor activity in transformed cells. Conversely, increasing macropinocytosis by Rabankyrin-5 overexpression was sufficient to enhance PDGFRβ activation in nontransformed cells. Simultaneous stimulation with PDGF-BB and epidermal growth factor promoted macropinocytosis of both receptors and increased their activation in nontransformed cells. We propose that H-Ras transformation promotes tumor progression by enhancing growth factor receptor signaling as a result of increased receptor macropinocytosis.

Critical role of the platelet-derived growth factor receptor (PDGFR) beta transmembrane domain in the TEL-PDGFRbeta cytosolic oncoprotein

The fusion of TEL with platelet-derived growth factor receptor (PDGFR) beta (TPbeta) is found in a subset of patients with atypical myeloid neoplasms associated with eosinophilia and is the archetype of a larger group of hybrid receptors that are produced by rearrangements of PDGFR genes. TPbeta is activated by oligomerization mediated by the pointed domain of TEL/ETV6, leading to constitutive activation of the PDGFRbeta kinase domain. The receptor transmembrane (TM) domain is retained in TPbeta and in most of the described PDGFRbeta hybrids. Deletion of the TM domain (DeltaTM-TPbeta) strongly impaired the ability of TPbeta to sustain growth factor-independent cell proliferation. We confirmed that TPbeta resides in the cytosol, indicating that the PDGFRbeta TM domain does not act as a transmembrane domain in the context of the hybrid receptor but has a completely different function. The DeltaTM-TPbeta protein was expressed at a lower level because of increased degradation. It could form oligomers, was phosphorylated at a slightly higher level, co-immunoprecipitated with the p85 adaptor protein, but showed a much reduced capacity to activate STAT5 and ERK1/2 in Ba/F3 cells, compared with TPbeta. In an in vitro kinase assay, DeltaTM-TPbeta was more active than TPbeta and less sensitive to imatinib, a PDGFR inhibitor. In conclusion, we show that the TM domain is required for TPbeta-mediated signaling and proliferation, suggesting that the activation of the PDGFRbeta kinase domain is not enough for cell transformation.

PDGF and vessel maturation

Pericytes are smooth muscle-like cells found in close contact with the endothelium in capillaries, where they regulate the morphology and function of the vessels. During vessel formation, platelet-derived growth factor-BB (PDGF-BB) is required for the recruitment and differentiation of pericytes. Tumor vessels display abnormal morphology and increased endothelial proliferation, resulting in leaky, tortuous vessels that are often poorly perfused. These vessels typically display decreased pericyte density, and the tumor-associated pericytes often express abnormal markers and show abnormal morphology. Anti-angiogenic therapy targeting pro-angiogenic growth factor pathways has been applied to a broad range of solid tumors with varying results. Studies utilizing mouse models indicate that the presence of pericytes protect endothelial cells against inhibition of vascular endothelial growth factor (VEGF) signaling. Simultaneous inhibition of PDGF receptors on pericytes therefore improves the effect of VEGF inhibitors on endothelial cells and enhances anti-angiogenic therapy.

Combined anti-angiogenic therapy targeting PDGF and VEGF receptors lowers the interstitial fluid pressure in a murine experimental carcinoma

Elevation of the interstitial fluid pressure (IFP) of carcinoma is an obstacle in treatment of tumors by chemotherapy and correlates with poor drug uptake. Previous studies have shown that treatment with inhibitors of platelet-derived growth factor (PDGF) or vascular endothelial growth factor (VEGF) signaling lowers the IFP of tumors and improve chemotherapy. In this study, we investigated whether the combination of PDGFR and VEGFR inhibitors could further reduce the IFP of KAT-4 human carcinoma tumors. The tumor IFP was measured using the wick-in-needle technique. The combination of STI571 and PTK/ZK gave an additive effect on the lowering of the IFP of KAT-4 tumors, but the timing of the treatment was crucial. The lowering of IFP following combination therapy was accompanied by vascular remodeling and decreased vascular leakiness. The effects of the inhibitors on the therapeutic efficiency of Taxol were investigated. Whereas the anti-PDGF and anti-VEGF treatment did not significantly inhibit tumor growth, the inhibitors enhanced the effect of chemotherapy. Despite having an additive effect in decreasing tumor IFP, the combination therapy did not further enhance the effect of chemotherapy. Simultaneous targeting of VEGFR and PDGFR kinase activity may be a useful strategy to decrease tumor IFP, but the timing of the inhibitors should be carefully determined.

Activation of protein kinase C alpha is necessary for sorting the PDGF beta-receptor to Rab4a-dependent recycling

Previous studies showed that loss of the T-cell protein tyrosine phosphatase (TC-PTP) induces Rab4a-dependent recycling of the platelet-derived growth factor (PDGF) beta-receptor in mouse embryonic fibroblasts (MEFs). Here we identify protein kinase C (PKC) alpha as the critical signaling component that regulates the sorting of the PDGF beta-receptor at the early endosomes. Down-regulation of PKC abrogated receptor recycling by preventing the sorting of the activated receptor into EGFP-Rab4a positive domains on the early endosomes. This effect was mimicked by inhibition of PKCalpha, using myristoylated inhibitory peptides or by knockdown of PKCalpha with shRNAi. In wt MEFs, short-term preactivation of PKC by PMA caused a ligand-induced PDGF beta-receptor recycling that was dependent on Rab4a function. Together, these observations demonstrate that PKC activity is necessary for recycling of ligand-stimulated PDGF beta-receptor to occur. The sorting also required Rab4a function as it was prevented by expression of EGFP-Rab4aS22N. Preventing receptor sorting into recycling endosomes increased the rate of receptor degradation, indicating that the sorting of activated receptors at early endosomes directly regulates the duration of receptor signaling. Activation of PKC through the LPA receptor also induced PDGF beta-receptor recycling and potentiated the chemotactic response to PDGF-BB. Taken together, our present findings indicate that sorting of PDGF beta-receptors on early endosomes is regulated by sequential activation of PKCalpha and Rab4a and that this sorting step could constitute a point of cross-talk with other receptors.

Identification of a subset of pericytes that respond to combination therapy targeting PDGF and VEGF signaling

The aim of our study was to further explore the use of anti-angiogenic therapy targeting the vascular endothelial growth factor receptor (VEGFR) on endothelial cells while simultaneously targeting platelet-derived growth factor receptors (PDGFRs) on adjacent pericytes. B16 mouse melanoma tumors exogenously expressing PDGF-BB (B16/PDGF-BB) display higher pericyte coverage on the vasculature compared to the parental B16 tumors (B16/mock). These models were used to investigate the effects of combination therapy targeting VEGFR and PDGFR signaling on size-matched tumors. Combination therapy using 25 mg/kg/day of the VEGFR inhibitor PTK787 and 100 mg/kg/day of the PDGFR inhibitor STI571 decreased the tumor growth rate of both tumor types, but the inhibition was only significant in the B16/PDGF-BB tumors. Combination therapy induced vessel remodeling, primarily by reducing the vessel density in B16/mock tumors, and by reducing the vessel size in B16/PDGF-BB tumors. When analyzing the effects of combination therapy on tumor vessel pericytes, it was found to primarily reduce the subpopulation of alpha-smooth muscle actin and PDGFRbeta-positive pericytes partly detached from the tumor vessels, without affecting the number of pericytes closely attached to the endothelium, which also express desmin. Taken together, these data demonstrate an increased benefit of targeting both VEGFR and PDGFR pathways in B16/PDGF-BB tumors, and demonstrates that the increased tumor growth inhibition in this model is accompanied by a reduction in a specific subset of pericytes, characterized by being loosely attached to endothelial cells and negative for the pericyte marker desmin.

An activating mutation in the PDGF receptor-beta causes abnormal morphology in the mouse placenta

An oncogenic D842V mutation in the platelet-derived growth factor (PDGF) alpha-receptor (Pdgfra) has recently been described in patients with gastrointestinal stromal tumors. In order to test if the same mutation would confer oncogenic properties to the homologous PDGF beta-receptor (Pdgfrb), the corresponding aspartic acid residue at position 849 of Pdgfrb was changed into valine (D849V) using a knock-in strategy. This mutation turned out to be dominantly lethal and caused death even in chimeras (from 345 transferred chimeric blastocysts, no living coat chimeras were detected). Experiments employing mouse embryonic fibroblasts (MEFs) indicated hyperactivity of the mutant receptor. The mutant receptor was phosphorylated in a ligand-independent manner and, in contrast to wild-type MEFs, mutant cells proliferated even in the absence of ligand. Knockout experiments have previously indicated a role for Pdgfrb in placental development. We therefore analyzed wild-type and Pdgfrb D849V chimeric placentas from different gestational stages. No differences were detected at embryonic days 11.5 and 13.5 (n=4). At embryonic day 17.5, however, chimeric placentas (n=3/4) displayed abnormalities both in the labyrinth and in the chorionic plate. The changes included hyper-proliferation of alpha-smooth muscle actin and platelet/endothelial cell adhesion molecule-1 positive cells in the labyrinth and cells in the chorionic plate. In addition, the fetal blood vessel compartment of the labyrinth was completely disorganized.

Dynamic changes in the expression of DEP-1 and other PDGF receptor-antagonizing PTPs during onset and termination of neointima formation

Growth factor-dependent tissue remodeling, such as restenosis, is believed to be predominantly regulated by changes in expression of receptor-tyrosine-kinases (RTKs) and their ligands. As endogenous antagonists of RTKs, protein-tyrosine-phosphatases (PTPs) are additional candidate regulators of these processes. Using laser-capture-microdissection and quantitative RT-polymerase chain reaction (qRT-PCR), we investigated the layer-specific expression of the four platelet-derived growth factor (PDGF) isoforms, the PDGF-alpha and beta receptors, and five PTPs implied in control of PDGF-receptor signaling 8 and 14 days after balloon injury of the rat carotid. Results were correlated with analyses of PDGF-beta receptor phosphorylation and vascular smooth muscle cell (VSMC) proliferation in vivo. The expression levels of all components, as well as receptor activation and VSMC proliferation, showed specific changes, which varied between media and neointima. Interestingly, PTP expression--particularly, DEP-1 levels--appeared to be the dominating factor determining receptor-phosphorylation and VSMC proliferation. In support of these findings, cultured DEP-1(-/-) cells displayed increased PDGF-dependent cell signaling. Hyperactivation of PDGF-induced signaling was also observed after siRNA-down-regulation of DEP-1 in VSMCs. The results indicate a previously unrecognized role of PDGF-receptor-targeting PTPs in controlling neointima formation. In more general terms, the observations indicate transcriptional regulation of PTPs as an important mechanism for controlling onset and termination of RTK-dependent tissue remodeling.

Loss of T-cell protein tyrosine phosphatase induces recycling of the platelet-derived growth factor (PDGF) beta-receptor but not the PDGF alpha-receptor

We have previously shown that the T-cell protein tyrosine phosphatase (TC-PTP) dephosphorylates the platelet-derived growth factor (PDGF) beta-receptor. Here, we show that the increased PDGF beta-receptor phosphorylation in TC-PTP knockout (ko) mouse embryonic fibroblasts (MEFs) occurs primarily on the cell surface. The increased phosphorylation is accompanied by a TC-PTP-dependent, monensin-sensitive delay in clearance of cell surface PDGF beta-receptors and delayed receptor degradation, suggesting PDGF beta-receptor recycling. Recycled receptors could also be directly detected on the cell surface of TC-PTP ko MEFs. The effect of TC-PTP depletion was specific for the PDGF beta-receptor, because PDGF alpha-receptor homodimers were cleared from the cell surface at the same rate in TC-PTP ko MEFs as in wild-type MEFs. Interestingly, PDGF alphabeta-receptor heterodimers were recycling. Analysis by confocal microscopy revealed that, in TC-PTP ko MEFs, activated PDGF beta-receptors colocalized with Rab4a, a marker for rapid recycling. In accordance with this, transient expression of a dominant-negative Rab4a construct increased the rate of clearance of cell surface receptors on TC-PTP ko MEFs. Thus, loss of TC-PTP specifically redirects the PDGF beta-receptor toward rapid recycling, which is the first evidence of differential trafficking of PDGF receptor family members.

Protein-tyrosine phosphatases and cancer

Tyrosine phosphorylation is an important signalling mechanism in eukaryotic cells. In cancer, oncogenic activation of tyrosine kinases is a common feature, and novel anticancer drugs have been introduced that target these enzymes. Tyrosine phosphorylation is also controlled by protein-tyrosine phosphatases (PTPs). Recent evidence has shown that PTPs can function as tumour suppressors. In addition, some PTPs, including SHP2, positively regulate the signalling of growth-factor receptors, and can be oncogenic. An improved understanding of how these enzymes function and how they are regulated might aid the development of new anticancer agents.

Identification and characterization of a novel splicing variant of vesicular monoamine transporter 1

Vesicular monoamine transporter 1 (VMAT1) is an integral protein in the membrane of secretory vesicles of neuroendocrine and endocrine cells that allows the transport of biogenic monoamines, such as serotonin, from the cytoplasm into the secretory vesicles. The full-length VMAT1 transcript is produced from 16 exons. We have identified and characterized an alternatively spliced form of VMAT1 that lacks exon 15, the next to last exon of VMAT1. The new form was therefore denoted VMAT1Delta15. Exon 15 does not contain an even multiple of three nucleotides. As a consequence, there is a shift of reading frame, and exon 16 is translated in an alternative reading frame, yielding a novel protein with a shorter and unrelated C-terminus compared with the native VMAT1 protein. VMAT1 and VMAT1Delta15 mRNAs are simultaneously expressed in normal and neoplastic neuroendocrine cells of the GI tract. However, VMAT1 expression is always higher than VMAT1Delta15 expression. We prove that VMAT1Delta15 is not localized in large, dense core vesicles as the native form but in the endoplasmic reticulum. Furthermore, while VMAT1 can take up serotonin, VMAT1Delta15 cannot, indicating different functions for the two forms of VMAT1.

A Gain of Function Mutation in the Activation Loop of Plateletderived Growth Factor β-Receptor Deregulates Its Kinase Activity

The platelet-derived growth factor receptors (PDGFRs) are receptor tyrosine kinases implicated in multiple aspects of cell growth, differentiation, and survival. Recently, a gain of function mutation in the activation loop of the human PDGFRalpha has been found in patients with gastrointestinal stromal tumors. Here we show that a mutation in the corresponding codon in the activation loop of the murine PDGFRbeta, namely an exchange of asparagine for aspartic acid at amino acid position 849 (D849N), confers transforming characteristics to embryonic fibroblasts from mutant mice, generated by a knock-in strategy. By comparing the enzymatic properties of the wild-type versus the mutant receptor protein, we demonstrate that the D849N mutation lowers the threshold for kinase activation, causes a dramatic alteration in the pattern of tyrosine phosphorylation kinetics following ligand stimulation, and induces a ligand-independent phosphorylation of several tyrosine residues. These changes result in deregulated recruitment of specific signal transducers. The GTPase-activating protein for Ras (RasGAP), a negative regulator of the Ras mitogenic pathway, displayed a delayed binding to the mutant receptor. Moreover, we have observed enhanced ligand-independent ERK1/2 activation and an increased proliferation of mutant cells. The p85 regulatory subunit of the phosphatidylinositol 3 '-kinase was constitutively associated with the mutant receptor, and this ligand-independent activation of the phosphatidylinositol 3'-kinase pathway may explain the observed strong protection against apoptosis and increased motility in cellular wounding assays. Our findings support a model whereby an activating point mutation results in a deregulated PDGFRbeta with oncogenic predisposition.

Site-selective regulation of platelet-derived growth factor beta receptor tyrosine phosphorylation by T-cell protein tyrosine phosphatase

The platelet-derived growth factor (PDGF) beta receptor mediates mitogenic and chemotactic signals. Like other tyrosine kinase receptors, the PDGF beta receptor is negatively regulated by protein tyrosine phosphatases (PTPs). To explore whether T-cell PTP (TC-PTP) negatively regulates the PDGF beta receptor, we compared PDGF beta receptor tyrosine phosphorylation in wild-type and TC-PTP knockout (ko) mouse embryos. PDGF beta receptors were hyperphosphorylated in TC-PTP ko embryos. Fivefold-higher ligand-induced receptor phosphorylation was observed in TC-PTP ko mouse embryo fibroblasts (MEFs) as well. Reexpression of TC-PTP partly abolished this difference. As determined with site-specific phosphotyrosine antibodies, the extent of hyperphosphorylation varied among different autophosphorylation sites. The phospholipase Cgamma1 binding site Y1021, previously implicated in chemotaxis, displayed the largest increase in phosphorylation. The increase in Y1021 phosphorylation was accompanied by increased phospholipase Cgamma1 activity and migratory hyperresponsiveness to PDGF. PDGF beta receptor tyrosine phosphorylation in PTP-1B ko MEFs but not in PTPepsilon ko MEFs was also higher than that in control cells. This increase occurred with a site distribution different from that seen after TC-PTP depletion. PDGF-induced migration was not increased in PTP-1B ko cells. In summary, our findings identify TC-PTP as a previously unrecognized negative regulator of PDGF beta receptor signaling and support the general notion that PTPs display site selectivity in their action on tyrosine kinase receptors.

Differential tyrosine phosphorylation of fibroblast growth factor (FGF) receptor-1 and receptor proximal signal transduction in response to FGF-2 and heparin

The sulfated regions in heparan sulfate and heparin are known to affect fibroblast growth factor (FGF) function. We have studied the mechanism whereby heparin directs FGF-2-induced FGF receptor-1 (FGFR-1) signal transduction. FGF-2 alone stimulated maximal phosphorylation of Src homology domain 2 tyrosine phosphatase (SHP-2) and the adaptor molecule Crk, in heparan sulfate-deficient Chinese hamster ovary (CHO) 677 cells expressing FGFR-1. In contrast, for phospholipase Cgamma(1) (PLCgamma(1)) and the adaptor molecule Shb to be maximally tyrosine-phosphorylated, cells had to be stimulated with both FGF-2 and heparin (100 ng/ml). Tyrosine residues 463 in the juxtamembrane domain and 766 in the C-terminal tail in FGFR-1 are known to bind Crk and PLCgamma(1), respectively. Analysis of tryptic phosphopeptide maps of FGFR-1 from cells stimulated with FGF-2 alone and FGF-2 together with heparin showed that FGF-2 alone stimulated a several-fold increase in tyrosine 463 in the juxtamembrane domain. In contrast, heparin had to be included in order for tyrosine 766 to be phosphorylated to the same fold level. Our data imply that tyrosine 463 is phosphorylated and able to transduce signals in response to FGF-2 treatment alone; furthermore, we suggest that FGFR-1 dimerization/kinase activation is stabilized by heparin.

Clustering of beta(2)-integrins on human neutrophils activates dual signaling pathways to PtdIns 3-kinase

The beta(2)-integrins on leukocytes can serve as a signaling unit during cell adhesion and locomotion, and to further clarify this important property we investigated the possible mechanisms of beta(2)-integrin-induced activation of PtdIns 3-kinase. It has previously been demonstrated that clustering of beta(2)-integrins activates p21(ras) by a tyrosine kinase-dependent pathway, and here we show that active p21(ras) interacts with its downstream target, PtdIns 3-kinase. Engagement of beta(2)-integrins also activates the tyrosine kinases p58(c-fgr) and p59/61(hck) and causes them to associate with the p85 subunit of PtdIns 3-kinase. These findings suggest a mechanism whereby p58(c-fgr) and p59/61(hck) are directly involved in the activation of PtdIns 3-kinase. No coupling between p58(c-fgr) and p59/61(hck) could be detected; hence these kinases probably trigger independent but parallel signals to PtdIns 3-kinase. The effect of beta(2)-integrin clustering on PtdIns 3-kinase activity was monitored as the activation of protein kinase B (PKB). Stimulation of PKB by beta(2)-integrins was abolished by genistein and wortmannin but not by using methyl transferase inhibitors to abrogate the influence of p21(ras)-related proteins. Thus, even if PtdIns 3-kinase is not activated by p21(ras), it can maintain full enzyme activity due to the mentioned interaction with p58(c-fgr) or p59/61(hck). These tyrosine kinases apparently activate similar pathways that operate in parallel and therefore have the potential to substitute for each other in mediating adhesion and regulating cell locomotion.

Disruption of beta(2)-integrin-cytoskeleton coupling abolishes the signaling capacity of these integrins on granulocytes

Integrin-dependent adhesion and dynamic modulations of the actin network are prerequisites for normal cell locomotion. To investigate whether the actin microfilamentous system does play a role in regulation of beta(2)-integrin-induced signalling, we pretreated granulocytes with staurosporine, a well-known protein kinase inhibitor that has also been shown to disrupt the cytoskeleton of intact cells. Pretreatment with staurosporine completely inhibited the beta(2)-integrin-induced Ca(2+) signal and also its ability to trigger actin polymerisation. This inhibition was not related to phosphorylation of the CD18-chain of the beta(2)-integrin, nor to inhibition of protein kinases. Instead, association of beta(2)-integrins with the cortical cytoskeleton, which was observed in untreated cells, was abolished after exposure to staurosporine, indicating that beta(2)-integrin signalling depends on integrin-cytoskeleton interaction. These results suggest not only that the actin network provides an adhesive link to the extracellular matrix and a driving force for the locomotory response, but also that it participates in regulation of beta(2)-integrin signalling during granulocyte locomotion.

Ca2+ signalling mechanisms of the beta 2 integrin on neutrophils: involvement of phospholipase C gamma 2 and Ins(1,4,5)P3

Engagement of beta 2 integrins triggers a tyrosine kinase-dependent intracellular mobilization and influx of Ca2+ in human neutrophils. However, the transduction pathway involved in generating this Ca2+ signal is obscure. In the present study we identified phospholipase C gamma 2 (PLC gamma 2) as one of the major proteins that was phosphorylated on tyrosine in response to beta 2 integrin activation. This beta 2 integrin-induced phosphorylation of PLC gamma 2 occurred in parallel with an increased accumulation of Ins(1,4,5)P3. The relevance of these observations for the beta 2 integrin-induced Ca2+ signal was investigated using an inhibitor of PLC signalling pathways, 1-(6-{[17 beta-3-methoxyoestra-1,3.5(10)-trien-17-yl] amino}hexyl)-1H-pyrrole-2,5-dione(U73122). U73122 dose-dependently (IC50, approx. 0.15 microM) inhibited both the beta 2 integrin-induced release of Ca2+ from intracellular stores and the subsequent influx of Ca2+ across the plasma membrane. These effects were not observed with the inactive analogue 1-(6-{[17 beta-3-methoxyoestra-1,3,5(10)-trien-17-yl] amino}hexyl)-pyrrolidine-2,5-dione (U73343). To gain further support for an involvement of PLC-induced Ins(1,4,5)P3 formation in the beta 2 integrin-induced Ca2+ signal, we searched for the molecular event(s) underlying the effects of U73122. Our experiments revealed that U73122 had no effect on either beta 2 integrin-induced tyrosine phosphorylation of PLC gamma 2 (or any of the other proteins) or on the formation of Ins(1,4,5)P3, but it reduced the Ins(1,4,5)P3-induced release of 45Ca2+ from intracellular stores of electropermeabilized cells. Taken together, the present data suggest that the beta 2 integrin-induced Ca2+ signal in human neutrophils is generated through activation of a PLC gamma 2-dependent pathway.

Inhibitors of farnesyl and geranylgeranyl methyltransferases prevent beta 2 integrin-induced actin polymerization without affecting beta 2 integrin-induced Ca2+ signaling in neutrophils

The role of prenylated proteins such as low molecular weight G-proteins (LMW G-proteins) in beta 2 integrin-dependent neutrophil signal transduction was investigated using two methyltransferase inhibitors, N-Acetyl-S-farnesyl-L-cysteine (AFC) and N-acetyl-s-geranylgeranyl-L-cysteine (AGGC), and an inactive control, N-acetyl-S-geranyl-L-cysteine (AGC). The drugs did not affect beta 2 integrin-induced protein tyrosine phosphorylations or cytosolic calcium transients. However, AGGC inhibited beta 2 integrin-induced actin polymerization (IC50 of approximately 45nM), as did AFC(IC50 of approximately 5.5 microM), but not AGC. Thus, prenylated proteins, such as LMW G-proteins, are responsible for beta 2 integrin regulation of actin filament reorganization downstream of tyrosine kinase(s) activation, and represent a beta 2 integrin signaling mechanism distinct from the pathway which regulates cytosolic calcium transients.

The Ca2+ signaling capacity of the beta 2-integrin on HL60-granulocytic cells is abrogated following phosphorylation of its CD18-chain: relation to impaired protein tyrosine phosphorylation

The phosphorylation state of the CD18-chain of beta 2-integrins have been shown not to mediate changes in the avidity of these receptors (i.e., inside-out signaling); however, no alternative functional significance has been proposed. Our study focused on how changes in the phosphorylation state of beta 2-integrin-receptors on HL60-granulocytic cells are related to its intracellular signal transduction properties (i.e., outside-in signaling). Engagement of beta 2-integrins on differentiated HL60 cells induced a transient increase in the cytosolic free Ca2+ concentration and an increased tyrosine phosphorylation of three major protein bands (70, 115, and 140 kDa). These signaling events occurred without any detectable phosphorylation of the CD18-chain. However, a strong phosphorylation of the CD18-chain by preexposure to phorbol myristate acetate (PMA) coincided with an abolishment of both the beta 2-integrin-induced Ca2+ signal and the protein tyrosine phosphorylations. By comparison, none of these effects were exhibited by 4-alpha-PMA, an analogue that does not activate protein kinase C. Thus, phosphorylation of the CD18-chain of beta 2-integrins is not required for outside-in signal transduction by these receptors, but it could constitute an effective mechanism by which the signaling properties of beta 2-integrins can be modulated by exogenous factors and possibly also by intracellular signals induced by other receptors. The fact that both the cytosolic free Ca2+ signal and protein tyrosine phosphorylations were abrogated by PMA suggests an intimate relationship between these two intracellular signals. To explore this possible relationship, we chelated the beta 2-integrin-induced Ca2+ signal with BAPTA. The beta 2-integrin-induced protein tyrosine phosphorylations were blocked by BAPTA but not by abolishment of the Ca2+ signal due to chelation with MAPT or by pretreatment with thapsigargin. These findings and the observation that pretreatment of cells with methyl-2,5-dihydroxycinnamate (a tyrosine kinase inhibitor) blocked the beta 2-integrin- but not the fMet-Leu-Phe-induced Ca2+ signal suggest that beta 2-integrin-induced tyrosine kinase activation occurs prior to and is a prerequisite for the subsequent Ca2+ signal.

Chemotactic factor receptor activation transiently impairs the Ca2+ signaling capacity of beta 2 integrins on human neutrophils

Neutrophil motility involves a delicate interplay between intracellular signals elicited by adhesion and chemotactic factor receptors. To explore certain aspects of these complex receptor interactions in neutrophils, we studied how engagement of the chemotactic receptor for N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe) and the beta 2 integrins affect the Ca2+ signaling properties of each other. Specific antibody engagement of the beta 2 integrins on suspended neutrophils generated both an intracellular mobilization and an influx of Ca2+, effects which could be temporarily impaired by preengaging the fMet-Leu-Phe receptors on the cells. In contrast to these findings, preengagement of the beta 2 integrins on suspended neutrophils affected neither a subsequent fMet-Leu-Phe-induced mobilization of Ca2+ nor an influx of Ca2+ from outside the cell. We also found that fMet-Leu-Phe could mobilize intracellular Ca2+ after a premobilization of Ca2+ via beta 2 integrins, despite the fact that both receptors mobilize Ca2+ from thapsigargin-sensitive intracellular stores. The findings that preactivation of beta 2 integrins did not affect the ability of fMet-Leu-Phe to induce an intracellular Ca2+ signal, whereas preactivation of fMet-Leu-Phe receptors transiently impaired the Ca2+ signaling ability of beta 2 integrins, suggest that the fMet-Leu-Phe-induced reduction is due to an interaction upstream of the release of Ca2+ from intracellular stores.

Complement receptor-mediated phagocytosis is associated with accumulation of phosphatidylcholine-derived diglyceride in human neutrophils. Involvement of phospholipase D and direct evidence for a positive feedback signal of protein kinase

Complement receptor (CR)-mediated phagocytosis is associated with an increased accumulation of diglyceride (sn-1,2-diacylglycerol and/or 1-O-alkyl-2-acyl-glycerol) in human neutrophils. The C3bi-mediated increase in diglyceride (5-20 min) was only partially impaired when phosphoinositide-specific phospholipase C (PLC) activity was abolished by reduction of cytosolic free Ca2+. At an early time point (1 min), however, diglyceride production was barely detectable in control cells, whereas production was considerable in cells with a reduced cytosolic free Ca2+ concentration. C3bi stimulation of 32P-labeled neutrophils caused a rapid and significant breakdown of [32P]phosphatidylcholine (PC) which was not affected by inhibition of Ca(2+)-dependent phosphoinositide-specific PLC. Thus, PC hydrolysis could be involved in C3bi-induced diglyceride formation. Stimulation of cells labeled with [3H]1-O-alkyl-lyso-PC ([3H]alkyl-lyso-PC), resulted in an increased formation of [3H]1-O-alkyl-phosphatidic acid ([3H]alkyl-PA) and a later and slower formation of [3H]1-O-alkyl-diglyceride ([3H]alkyl-diglyceride); this suggests activation of phospholipase D (PLD). When these labeled cells were stimulated in the presence of 0.5% ethanol a marked accumulation of [3H]1-O-alkyl-phosphatidylethanol ([3H]alkyl-PEt) was observed in both controls and calcium-reduced cells, further strengthening the suggested involvement of PLD activity. In parallel with the sustained increase in diglyceride formation, CR-mediated phagocytosis was also associated with phosphorylation of a cellular protein kinase C substrate (MARCKS). Therefore it seems reasonable to suggest a causal relationship between C3bi-induced PLD activation, which results in diglyceride formation, and activation of protein kinase C. In electropermeabilized cells which were incapable of ingesting particles, C3bi particles were still able to activate PLD and induce formation of diglyceride. This signaling event must therefore be triggered by binding of particles to the cell and not by the engulfment process. Most importantly, introduction of the protein kinase C inhibitor peptides, PKC(19-36) and PKC(19-31), into these permeabilized cells resulted in a clear reduction of the C3bi-induced production of diglyceride, indicating that CR-mediated activation of protein kinase C directly triggers a positive feedback mechanism for additional diglyceride formation. Taken together, these data further clarify the mechanisms of CR-mediated diglyceride formation and give added support to the concept that protein kinase C plays an important role in the phagocytic process.

Absenteeism because of illness at daycare centers and in three-family systems

Absenteeism because of illness was recorded for 346 children and 98 staff members at eight daycare centers in Gothenburg during a nine-month period between October 1987 and June 1988. A comparison was made with a similar, nationwide study, carried out in 1977 by the Swedish Central Bureau of Statistics. This comparison demonstrated that the absence of children and employees from daycare centers for health reasons was of the same proportion in the present study as that reported a decade earlier. Absenteeism because of illness among the 346 children at the daycare centers was also compared with absenteeism among 49 children in 14 groups run according to the three-family system (three to six children/group). It was found that absenteeism was at least twice as frequent among children at daycare centers than among those in the three-family system.