DRR drives brain cancer invasion by regulating cytoskeletal-focal adhesion dynamics.

Malignant glioma invasion is a primary cause of brain cancer treatment failure, yet the molecular mechanisms underlying its regulation remain elusive. We developed a novel functional-screening strategy and identified downregulated in renal cell carcinoma (DRR) as a regulator of invasion. We show that DRR drives invasion in vitro and in vivo. We found that while DRR is not expressed in normal glial cells, it is highly expressed in the invasive component of gliomas. Exploring underlying mechanisms, we show that DRR associates with and organizes the actin and microtubular cytoskeletons and that these associations are essential for focal adhesion (FA) disassembly and cell invasion. These findings identify DRR as a new cytoskeletal crosslinker that regulates FA dynamics and cell movement.

Inhibition of medulloblastoma cell invasion by Slit.

Invasion of brain tumor cells has made primary malignant brain neoplasms among the most recalcitrant to therapeutic strategies. We tested whether the secreted protein Slit2, which guides the projection of axons and developing neurons, could modulate brain tumor cell invasion. Slit2 inhibited the invasion of medulloblastoma cells in a variety of in vitro models. The effect of Slit2 was inhibited by the Robo ectodomain. Time-lapse videomicroscopy indicated that Slit2 reduced medulloblastoma invasion rate without affecting cell direction or proliferation. Both medulloblastoma and glioma tumors express Robo1 and Slit2, but only medulloblastoma invasion is inhibited by recombinant Slit2 protein. Downregulation of activated Cdc42 may contribute to this differential response. Our findings reinforce the concept that neurodevelopmental cues such as Slit2 may provide insights into brain tumor invasion.

E6/E7 oncogenes increase and tumor suppressors decrease the proportion of self-renewing neural progenitor cells.

Many if not most tissues need a controlled number of stem cells to maintain normal function. Cancer can be seen as a process of disturbed tissue homeostasis, in which too many cells have or acquire too primitive identity. Here we measured how oncogenes and tumour suppressors affect the differentiation capacity, proportion and characteristics of progenitor cells in a model tissue. Neural progenitor cells (NPCs) were exposed to human papilloma virus E6, E7 or E6/E7 oncogenes, which degrade tumour suppressors p53 and pRb family members, respectively. E6/E7-expressing or p53-/- NPCs were able to differentiate, but simultaneously retained high capacity for self-renewal, proliferation, ability to remain multipotent in conditions promoting differentiation and showed delayed cell cycle exit. These functions were mediated through p53 and pRb family, and involved MEK-ERK signalling. Decreased amount of p53 increased self-renewal and proliferation, whereas pRb affected only proliferation. Our results suggest that the oncogenes increase whereas p53 and pRb family tumour suppressors decrease the number and proportion of progenitor cells. These findings provide one explanation how oncogenes and tumour suppressors control tissue homeostasis and highlight their importance in stem cell self- renewal, linked both to cancer and life-long tissue turnover.

Protein tyrosine phosphatase-PEST regulates focal adhesion disassembly, migration, and cytokinesis in fibroblasts.

In this article, we show that, in transfected COS-1 cells, protein tyrosine phosphatase (PTP)-PEST translocates to the membrane periphery following stimulation by the extracellular matrix protein fibronectin. When plated on fibronectin, PTP-PEST (-/-) fibroblasts display a strong defect in motility. 3 h after plating on fibronectin, the number and size of vinculin containing focal adhesions were greatly increased in the homozygous PTP-PEST mutant cells as compared with heterozygous cells. This phenomenon appears to be due in part to a constitutive increase in tyrosine phosphorylation of p130(CAS), a known PTP-PEST substrate, paxillin, which associates with PTP-PEST in vitro, and focal adhesion kinase (FAK). Another effect of this constitutive hyperphosphorylation, consistent with the focal adhesion regulation defect, is that (-/-) cells spread faster than the control cell line when plated on fibronectin. In the PTP-PEST (-/-) cells, an increase in affinity for the SH2 domains of Src and Crk towards p130(CAS) was also observed. In (-/-) cells, we found a significant increase in the level of tyrosine phosphorylation of PSTPIP, a cleavage furrow-associated protein that interacts physically with all PEST family members. An effect of PSTPIP hyperphosphorylation appears to be that some cells remain attached at the site of the cleavage furrow for an extended period of time. In conclusion, our data suggest PTP-PEST plays a dual role in cell cytoskeleton organization, by promoting the turnover of focal adhesions required for cell migration, and by directly or indirectly regulating the proline, serine, threonine phosphatase interacting protein (PSTPIP) tyrosine phosphorylation level which may be involved in regulating cleavage furrow formation or disassembly during normal cell division.

Roles of protein tyrosine phosphatases in cell migration and adhesion.

Signal transduction pathways are often seen as cascades of kinases, whereas phosphatases are relinquished to the housekeeping function of resetting the individual elements to a resting state. However, critical biological processes such as cellular migration require a coordinated and constant remodeling of the actin cytoskeleton as well as a rapid turnover of the cell-substratum linkages that necessitate the concomitant action of antagonistic enzymes. Tyrosine phosphorylation was long known to be involved in adhesion and de-adhesion mediated via the integrin receptors. As the roles of tyrosine kinases such as focal adhesion kinase, c-Src, and Csk in this pathway are being extensively studied, increasing evidence is emerging about the importance of protein tyrosine phosphatases (PTP). In this review we discuss examples of PTPs that were recently shown to play a role in cell adhesion and migration and their mechanism of action.