Brain endothelial cells promote breast cancer cell extravasation to the brain via EGFR-DOCK4-RAC1 signalling.

The role of endothelial cells in promoting cancer cell extravasation to the brain during the interaction of cancer cells with the vasculature is not well characterised. We show that brain endothelial cells activate EGFR signalling in triple-negative breast cancer cells with propensity to metastasise to the brain. This activation is dependent on soluble factors secreted by brain endothelial cells, and occurs via the RAC1 GEF DOCK4, which is required for breast cancer cell extravasation to the brain in vivo. Knockdown of DOCK4 inhibits breast cancer cell entrance to the brain without affecting cancer cell survival or growth. Defective extravasation is associated with loss of elongated morphology preceding intercalation into brain endothelium. We also show that brain endothelial cells promote paracrine stimulation of mesenchymal-like morphology of breast cancer cells via DOCK4, DOCK9, RAC1 and CDC42. This stimulation is accompanied by EGFR activation necessary for brain metastatic breast cancer cell elongation which can be reversed by the EGFR inhibitor Afatinib. Our findings suggest that brain endothelial cells promote metastasis through activation of cell signalling that renders breast cancer cells competent for extravasation. This represents a paradigm of brain endothelial cells influencing the signalling and metastatic competency of breast cancer cells.

MICAL2 enhances branched actin network disassembly by oxidizing Arp3B-containing Arp2/3 complexes.

The mechanisms regulating the disassembly of branched actin networks formed by the Arp2/3 complex still remain to be fully elucidated. In addition, the impact of Arp3 isoforms on the properties of Arp2/3 are also unexplored. We now demonstrate that Arp3 and Arp3B isocomplexes promote actin assembly equally efficiently but generate branched actin networks with different disassembly rates. Arp3B dissociates significantly faster than Arp3 from the network, and its depletion increases actin stability. This difference is due to the oxidation of Arp3B, but not Arp3, by the methionine monooxygenase MICAL2, which is recruited to the actin network by coronin 1C. Substitution of Arp3B Met293 by threonine, the corresponding residue in Arp3, increases actin network stability. Conversely, replacing Arp3 Thr293 with glutamine to mimic Met oxidation promotes disassembly. The ability of MICAL2 to enhance network disassembly also depends on cortactin. Our observations demonstrate that coronin 1C, cortactin, and MICAL2 act together to promote disassembly of branched actin networks by oxidizing Arp3B-containing Arp2/3 complexes.

Efficacy of a film-forming medical device containing sunscreen (50+) and piroxicam 0.8% in actinic keratosis and field cancerization: a multicenter, assessor-blinded, 3 month trial.

INTRODUCTION: Sunscreen protection in subjects with actinic keratosis (AK) is highly recommended to prevent clinical evolution of this in situ skin cancer condition. Use of topical anti-cyclooxygenase drugs such as diclofenac and piroxicam reduces the number of lesions and improves the cancerization field. A film-forming medical device in a cream formulation containing organic and inorganic sun-filters (50+ SPF) and piroxicam 0.8% (ACTX) has shown in a pilot, single-center, open trial to reduce AK lesions improving the cancerization field. AIM: We evaluated in a multicenter, assessor-blinded, 3 month trial the efficacy of ACTX in AK. METHODS: A total of 70 subjects with at least three AK lesions on the scalp or face were enrolled after written informed consent. Primary outcomes of the study were the clinical evolution of number of AK lesions on a target zone area and the evolution of dermoscopy features of the target lesion, assessing erythema, scaling, pigmentation, and follicular plug, using a 5 point score (from 0 to 4; maximum score: 16). Lesion count and dermoscopy score were evaluated in a blind fashion assessing digital color high definition coded images. A secondary outcome was the Investigator Global Score (IGS) of clinical evolution of the target area using a 7 point scale from -2 (significantly worse) to +4 (completely cured). IGS was evaluated in an open fashion. Subjects were instructed to apply the cream twice daily on the target area, using one finger-tip unit for the treatment of a 35 cm2 area. RESULTS: All but one subject (40 men and 30 women, mean age 73 years) concluded the study period. At baseline the mean (±SD) number of AK lesions in the target area were 7.0 (5.9) with a median value of 5 and the dermoscopy score of the target lesion was 7.0 (2.3) with a median value of 7.0. ACTX treatment reduced AK lesions to 3.2 (2.9), (p = .0001; Wilcoxon Test), representing a 55% relative reduction. Dermoscopy score was reduced to 3.3 (2.6) (p = .0001) (a reduction of 53%). The IGS after ACTX treatment was +1.9 (1.1), with a median of 2.0. A total of 86% of subjects showed a clinical improvement of IGS (≥1) with a very significant/complete clearance (score +3 or +4) in 42% subjects. No change or a worsening of AK lesions was observed in 14% of the subjects. The product was well tolerated. No serious adverse events were reported during the duration of the trial. CONCLUSION: In this multicenter, assessor-blinded trial, the use of a film-forming medical device with sun protection and anti-inflammatory actions was effective in reducing AK lesions and improving the dermoscopy aspect of the target lesion in 86% of treated subjects. A head-to-head trial evaluating the efficacy of this medical device in comparison with diclofenac is warranted to establish whether this therapeutic approach could offer additional advantages in term of AK lesion reduction compared to an established topical treatment. (Trial ID: ISRCTN72020277).

Isoform diversity in the Arp2/3 complex determines actin filament dynamics.

The Arp2/3 complex consists of seven evolutionarily conserved subunits (Arp2, Arp3 and ARPC1-5) and plays an essential role in generating branched actin filament networks during many different cellular processes. In mammals, however, the ARPC1 and ARPC5 subunits are each encoded by two isoforms that are 67% identical. This raises the possibility that Arp2/3 complexes with different properties may exist.  We found that Arp2/3 complexes containing ARPC1B and ARPC5L are significantly better at promoting actin assembly than those with ARPC1A and ARPC5, both in cells and in vitro. Branched actin networks induced by complexes containing ARPC1B or ARPC5L are also disassembled ∼2-fold slower than those formed by their counterparts. This difference reflects the ability of cortactin to stabilize ARPC1B- and ARPC5L- but not ARPC1A- and ARPC5-containing complexes against coronin-mediated disassembly. Our observations demonstrate that the Arp2/3 complex in higher eukaryotes is actually a family of complexes with different properties.

Cytoplasmatic compartmentalization by Bcr-Abl promotes TET2 loss-of-function in chronic myeloid leukemia.

The loss-of-function of ten-eleven-translocation (TET) 2, a Fe(2+) -oxoglutarate-dependent dioxygenase catalyzing 5 methyl cytosine (5mC) conversion into 5-hydroxymethylcytosine (5hmC), contributes to the hematopoietic transformation in vivo. The aim of our study was to elucidate its role in the phenotype of chronic myeloid leukemia (CML), a myeloproliferative disease caused by the Bcr-Abl rearranged gene. We first confirmed TET2 interaction with the Bcr-Abl protein predicted by a Fourier-based bioinformatic method. Such interaction led to TET2 cytoplasmatic compartmentalization in a complex tethered by the fusion protein tyrosine kinase (TK) and encompassing the Forkhead box O3a (FoxO3a) transcription factor. We then focused the impact of TET2 loss-of-function on epigenetic transcriptional regulation of Bcl2-interacting mediator (BIM), a pro-apoptotic protein transcriptionally regulated by FoxO3a. BIM downregulation is a critical component of CML progenitor extended survival and is also involved in the disease resistance to imatinib (IM). Here we reported that TET2 release from Bcr-Abl protein following TK inhibition in response to IM triggers a chain of events including TET2 nuclear translocation, re-activation of its enzymatic function at 5mC and recruitment at the BIM promoter followed by BIM transcriptional induction. 5hmC increment following TET2 re-activation was associated with the reduction of histone H3 tri-methylation at lysine 9 (H3K9me3), which may contribute with DNA de-methylation reported elsewhere to recast a permissive epigenetic "landscape" for FoxO3a transcriptional activity.