Autocrine signaling can explain the emergence of Allee effects in cancer cell populations

In many human cancers, the rate of cell growth depends crucially on the size of the tumour cell population. Low, zero, or negative growth at low population densities is known as the Allee effect; this effect has been studied extensively in ecology, but so far lacks a good explanation in the cancer setting. Here, we formulate and analyze an individual-based model of cancer, in which cell division rates are increased by the local concentration of an autocrine growth factor produced by the cancer cells themselves. We show, analytically and by simulation, that autocrine signaling suffices to cause both strong and weak Allee effects. Whether low cell densities lead to negative (strong effect) or reduced (weak effect) growth rate depends directly on the ratio of cell death to proliferation, and indirectly on cellular dispersal. Our model is consistent with experimental observations from three patient-derived brain tumor cell lines grown at different densities. We propose that further studying and quantifying population-wide feedback, impacting cell growth, will be central for advancing our understanding of cancer dynamics and treatment, potentially exploiting Allee effects for therapy

A cluster of genes located in 1p36 are down-regulated in neuroblastomas with poor prognosis, but not due to CpG island methylation

BACKGROUND: A common feature of neuroblastoma tumours are partial deletions of the short arm of chromosome 1 (1p-deletions). This is indicative of a neuroblastoma tumour suppressor gene being located in the region. Several groups including our have been studying candidate neuroblastoma genes in the region, but no gene/genes have yet been found that fulfil the criteria for being a neuroblastoma tumour suppressor. Since frequent mutations have not been detected, we have now analyzed the expression and promoter CpG island methylation status of the genes UBE4B, KIF1B, PGD, APITD1, DFFA and PEX14 in the 1p36.22 region in order to find an explanation for a possible down-regulation of this region. RESULTS: The current study shows that gene transcripts in high stage neuroblastoma tumours are significantly down-regulated compared to those in low stage tumours in the 1p36.22 region. CpG island methylation does not seem to be the mechanism of down-regulation for most of the genes tested, since no methylation was detected in the fragments analyzed. One exception is the CpG island of APITD1. Methylation of this gene is also seen in blood from control individuals and is therefore not believed to participate in tumour development. CONCLUSION: The genes UBE4B, KIF1B, PGD, APITD1, DFFA and PEX14 are down-regulated in high stage NB tumours, a feature that can not be explained by CpG island methylation

Identification and characterization of candidate genes for neuroblastoma development

Aim: Neuroblastoma (NB) is the most common tumor during infancy. It arises from undifferentiated cells in the sympathetic nervous system and is characterized by both clinical and genetic heterogeneity. One of the features of NBs with unfavorable outcome is loss on distal chromosome 1p. The aim of this thesis was to identify genetic factors with relevance for NB tumorigenesis, with special emphasis on the tumor suppressor candidate region on chromosome 1p36.2.Results: All known genes (UBE4B, KIF1B, PGD, CORT, DFFA and PEX14) in the hotspot NB tumor suppressor gene region on 1p36.22 were screened for mutations by capillary-based sequencing of DNA from a large series of NB tumors. The potential tumor suppressor properties of the genes ENO1, ICAT and CASP9, located close to this region, were also analyzed. A few mutations with predicted deleterious effects on protein function were found in the apoptotic regulator DFFA and in the UBE4B gene, which is involved in selective protein degradation. We were also able to show that expression of ENO1, DFFA, UBE4B and CASP9, critical for induction of the apoptotic cascade, is down-regulated in tumors with unfavorable outcome. We identified a novel gene, denoted APITD1, in 1p36.22; two alternative transcripts of this gene were abundantly expressed in normal adult and fetal tissues. Primary NB tumors showed either very weak or no measurable APITD1 expression and the lowest levels were detected in tumors with unfavorable outcome. The coding sequence of APITD1 was well-conserved in different species and no coding variations were found in primary NB tumors. Anti-proliferative and apoptotic effects were observed after over-expression of APITD1 and ENO1 in NB cell lines and in embryonal kidney- derived cells. A mutated ENO1 construct was used to show that the glycolytic enzyme á-enolase had as strong an effect on cell proliferation as the other translational product, MBP1, which is a negative regulator of the c-Myc oncogene. Biallelic inactivation of the transcription factor PHOX2B on chromosome 4p was found in a patient with multifocal NB, emphasizing the importance of early embryologic differentiation pathways in tumors of neural crest origin. Conclusions: A few rare mutations were found in genes with possible tumor suppressor functions. Several genes on 1p36.2 were also shown to be down-regulated in aggressive tumors. We therefore propose that the poor prognosis for NB patients with 1p deletions is a syngenic effect of mutations or transcriptional silencing of several genes in this region

Vad kan evidensbaserad praktik vara? : Några socialarbetare talar om evidensbaserat arbete

Denna kvalitativa studie belyser hur socialarbetare inom missbruksvården uttalade sig om evidensbaserad praktik. Syftet var även att få en förståelse i vad som kan hindra eller främja ett evidensbaserat arbetssätt. Studien utgick ifrån en socialkonstruktivistisk ansats genom Berger och Luckmanns tresidiga modell där även studiens resultat är tolkat i samma anda. Studien gjordes utefter semistrukturerad utgångspunkt med fem socialarbetare inom missbruksvården i sammanlagt tre kommuner. Resultatet visar att evidensbaserad praktik ses som något som är beforskat och beprövat. I övrigt ligger delade meningar i begreppets innebörd. Vad som kan ses som ett hinder i implementeringen av evidenbaserad praktik är att hamna i ett tänk där klienten får anpassa sig efter organisationen och inte tvärt om. Det som möjliggör evidensbaserad praktik är ett gemensamt arbetssätt för socialarbetarna. En slutsats är att det finns en ambition om ett evidensbaserat arbetssätt men att det finns många hinder på vägen mot en evidensbaserad socialtjänst

Autocrine signaling can explain the emergence of Allee effects in cancer cell populations

In many human cancers, the rate of cell growth depends crucially on the size of the tumour cell population. Low, zero, or negative growth at low population densities is known as the Allee effect; this effect has been studied extensively in ecology, but so far lacks a good explanation in the cancer setting. Here, we formulate and analyze an individual-based model of cancer, in which cell division rates are increased by the local concentration of an autocrine growth factor produced by the cancer cells themselves. We show, analytically and by simulation, that autocrine signaling suffices to cause both strong and weak Allee effects. Whether low cell densities lead to negative (strong effect) or reduced (weak effect) growth rate depends directly on the ratio of cell death to proliferation, and indirectly on cellular dispersal. Our model is consistent with experimental observations from three patient-derived brain tumor cell lines grown at different densities. We propose that further studying and quantifying population-wide feedback, impacting cell growth, will be central for advancing our understanding of cancer dynamics and treatment, potentially exploiting Allee effects for therapy

Mutations in the N-terminal domain of DFF45 in a primary germ cell tumor and in neuroblastoma tumors.

DFF45 has essential functions in the final stage of apoptosis by acting both as a folding chaperone and a DNase inhibitor of DFF40. The gene encoding DFF45 (DFFA) maps to the consensus deleted region in primary neuroblastoma (NB; 1p36.2-3) and within the homozygously deleted region in an NB cell line (1p36.2). DFF45 is therefore an attractive candidate NB tumor suppressor. In a previous study we found a rare allele variant, causing a non-polar to a polar amino acid exchange (Ile69Thr) in a preserved hydrophobic patch of DFF45, and we also found DFFA to be preferentially expressed in favorable NB tumors. We have extended the previous study and performed mutation analyses in another 56 NB tumors (100 in total) as well as a set of other tumors for coding mutations in DFFA. We have also performed studies of the DFFA expression in tumors using real-time PCR. We found a missense mutation (Ile15Met) in the remaining allele of a teratoma with heterozygous deletion of 1p, and a three base-pair deletion in an NB of unknown stage causing a deletion of amino acid 37 in DFF45. The one-base substitution detected in the teratoma was not present in the patients constitutional DNA, i.e. it is a true mutation present in the tumor DNA only. In conclusion, three different coding alterations have been found in the region encoding the N-terminal regulatory domain of DFF45, responsible for binding and achieving its chaperone and inhibitor functions on other proteins. Moreover, by real-time RT-PCR expression study, we found the mRNA level of DFFA to be significantly (p=0.038) reduced by a factor of 1.7 times in NB tumors of unfavorable outcome

Mutations in the N-terminal domain of DFF45 in a primary germ cell tumor and in neuroblastoma tumors.

DFF45 has essential functions in the final stage of apoptosis by acting both as a folding chaperone and a DNase inhibitor of DFF40. The gene encoding DFF45 (DFFA) maps to the consensus deleted region in primary neuroblastoma (NB; 1p36.2-3) and within the homozygously deleted region in an NB cell line (1p36.2). DFF45 is therefore an attractive candidate NB tumor suppressor. In a previous study we found a rare allele variant, causing a non-polar to a polar amino acid exchange (Ile69Thr) in a preserved hydrophobic patch of DFF45, and we also found DFFA to be preferentially expressed in favorable NB tumors. We have extended the previous study and performed mutation analyses in another 56 NB tumors (100 in total) as well as a set of other tumors for coding mutations in DFFA. We have also performed studies of the DFFA expression in tumors using real-time PCR. We found a missense mutation (Ile15Met) in the remaining allele of a teratoma with heterozygous deletion of 1p, and a three base-pair deletion in an NB of unknown stage causing a deletion of amino acid 37 in DFF45. The one-base substitution detected in the teratoma was not present in the patients constitutional DNA, i.e. it is a true mutation present in the tumor DNA only. In conclusion, three different coding alterations have been found in the region encoding the N-terminal regulatory domain of DFF45, responsible for binding and achieving its chaperone and inhibitor functions on other proteins. Moreover, by real-time RT-PCR expression study, we found the mRNA level of DFFA to be significantly (p=0.038) reduced by a factor of 1.7 times in NB tumors of unfavorable outcome

Inference of glioblastoma migration and proliferation rates using single time-point images

Cancer cell migration is a driving mechanism of invasion in solid malignant tumors. Anti-migratory treatments provide an alternative approach for managing disease progression. However, we currently lack scalable screening methods for identifying novel anti-migratory drugs. To this end, we develop a method that can estimate cell motility from single end-point images in vitro by estimating differences in the spatial distribution of cells and inferring proliferation and diffusion parameters using agent-based modeling and approximate Bayesian computation. To test the power of our method, we use it to investigate drug responses in a collection of 41 patient-derived glioblastoma cell cultures, identifying migration-associated pathways and drugs with potent anti-migratory effects. We validate our method and result in both in silico and in vitro using time-lapse imaging. Our proposed method applies to standard drug screen experiments, with no change needed, and emerges as a scalable approach to screen for anti-migratory drugs. The spatial positioning of cultured glioblastoma cells is used to estimate cell motility and drug effects from single end-point images in vitro

Introduction of <it>in vitro </it>transcribed <it>ENO1 </it>mRNA into neuroblastoma cells induces cell death

Abstract Background Neuroblastoma is a solid tumour of childhood often with an unfavourable outcome. One common genetic feature in aggressive tumours is 1p-deletion. The α-enolase (ENO1) gene is located in chromosome region 1p36.2, within the common region of deletion in neuroblastoma. One alternative translated product of the ENO1 gene, known as MBP-1, acts as a negative regulator of the c-myc oncogene, making the ENO1 gene a candidate as a tumour suppressor gene. Methods Methods used in this study are transfection of cDNA-vectors and in vitro transcribed mRNA, cell growth assay, TUNEL-assay, real-time RT-PCR (TaqMan) for expression studies, genomic sequencing and DHPLC for mutation detection. Results Here we demonstrate that transfection of ENO1 cDNA into 1p-deleted neuroblastoma cell lines causes' reduced number of viable cells over time compared to a negative control and that it induces apoptosis. Interestingly, a similar but much stronger dose-dependent reduction of cell growth was observed by transfection of in vitro transcribed ENO1 mRNA into neuroblastoma cells. These effects could also be shown in non-neuroblastoma cells (293-cells), indicating ENO1 to have general tumour suppressor activity. Expression of ENO1 is detectable in primary neuroblastomas of all different stages and no difference in the level of expression can be detected between 1p-deleted and 1p-intact tumour samples. Although small numbers (11 primary neuroblastomas), there is some evidence that Stage 4 tumours has a lower level of ENO1-mRNA than Stage 2 tumours (p = 0.01). However, mutation screening of 44 primary neuroblastomas of all different stages, failed to detect any mutations. Conclusion Our studies indicate that ENO1 has tumour suppressor activity and that high level of ENO1 expression has growth inhibitory effects.</p