ADP Ribosylation Factor Like 2 (Arl2) Regulates Breast Tumor Aggressivity in Immunodeficient Mice

We have previously reported that ADP ribosylation factor like 2 (Arl2), a small GTPase, content influences microtubule dynamics and cell cycle distribution in breast tumor cells, as well as the degree and distribution of phosphorylated P53. Here we show, in two different human breast adenocarcinoma models, that Arl2 content has a major impact on breast tumor cell aggressivity both in vitro and in vivo. Cells with reduced content of Arl2 displayed reduced contact inhibition, increased clonogenic or cluster formation as well as a proliferative advantage over control cells in an in vitro competition assay. These cells also caused larger tumors in SCID mice, a phenotype which was mimicked by the in vivo administration of siRNA directed against Arl2. Cells with increased Arl2 content displayed reduced aggressivity, both in vitro and in vivo, with enhanced necrosis and were also found to contain increased PP2A phosphatase activity. A rt-PCR analysis of fresh human tumor breast samples suggested that low Arl2 expression was associated with larger tumor size and greater risk of lymph node involvement at diagnosis. These data underline the role of Arl2, a small GTPase, as an important regulator of breast tumor cell aggressivity, both in vitro and in vivo

Dysregulation of Ribosome Biogenesis and Translational Capacity Is Associated with Tumor Progression of Human Breast Cancer Cells

Protein synthesis is a fundamental cell process and ribosomes - particularly through the ribosomal RNA that display ribozyme activity - are the main effectors of this process. Ribosome biogenesis is a very complex process involving transcriptional a

Effect of <i>in vivo</i> siRNA directed against Arl2 or PP2A on human MDA-MB-231 xenografts.

<p>SCID mice were injected subcutaneously on day 1 (black triangle) with MDA-MB 231 cells then treated daily, 5 days a week for 4 weeks with siRNA (scrambled continous line), directed against Arl2 (dotted line), directed against PP2A (dashed line). *Significant differences were observed between the groups receiving scrambled and Arl2 or PP2A directed siRNA (p<0.05). Arrows represent siRNA injections.</p

Arl2 content influences tumorigenesis.

<p>A: Representative images of non invasive bioluminescent follow up (from day 17 to day 36) for a same tumor of each cell lines (MdaA-.luc, MdaP.luc, MdaA+.luc) developed from mice mammary fat pad injected cells. B: Mean rates of tumoral bioluminescence in mice expressed in photons/sec for each day and sublines. Tumor growths (R-growths) were evaluated using a linear projection of the growth curve (red) and expressed in arbitrary units per day (AU/day). Bars represent standard deviations. Statistical significance was determined using Student's t test. C: Representative images of histochemistry of MdaA-, MdaP, MdaA+ cells tumors slides at day 22, 29 and 36. Black arrows show necrotic regions (in light pink) which are particularly important in MdaA+ cells tumors.</p

Effect of Arl2 content on three-dimensional cell growth.

<p>A: Soft agar and soft agar complemented with matrigel (30% v/v) assay for MA-, MP and MA+ cells expressed in colonies number (left) and in area means (right). Bars represented standard deviations. Statistical significance was determined using Student's t test. B: Follow up of MA-, MP and MA+ cells overlayed on matrigel. Representative images displayed cellular colonies growth from day 6 to Day 20 after cells seeding. C: Matrigel cluster assay performed for MdaA-, MdaP and MdaA+ cells. Light blue lines represent the contour of cells clusters at day 2 and dark blue lines at day 5 after cells seeding (left, representative images). Mean rates of cluster growth were evaluated by daily measurements of cell clusters areas from day 2 to day 5. Bars represented standard deviations. Statistical significance was determined using Student's t test.</p

Tumor size and lymph node involvement in primary human breast tumors according to Arl2 expression levels.

<p>Arl2 levels were determined by quantitative rt-PCR on frozen primary breast tumors.</p