Ephrin-B3 supports glioblastoma growth by inhibiting apoptosis induced by the dependence receptor EphA4.

EphA4, an Ephrins tyrosine kinase receptor, behaves as a dependence receptor (DR) by triggering cell apoptosis in the absence of its ligand Ephrin-B3. DRs act as conditional tumor suppressors, engaging cell death based on ligand availability; this mechanism is bypassed by overexpression of DRs ligands in some aggressive cancers. The pair EphA4/Ephrin-B3 favors survival of neuronal progenitors of the brain subventricular zone, an area where glioblastoma multiform (GBM) are thought to originate. Here, we report that Ephrin-B3 is highly expressed in human biopsies and that it inhibits EphA4 pro-apoptotic activity in tumor cells. Angiogenesis is directly correlated with GBM aggressiveness and we demonstrate that Ephrin-B3 also supports the survival of endothelial cells in vitro and in vivo. Lastly, silencing of Ephrin-B3 decreases tumor vascularization and growth in a xenograft mice model. Interference with EphA4/Ephrin-B3 interaction could then be envisaged as a relevant strategy to slow GBM growth by enhancing EphA4-induced cell death.

Stability of the Peutz-Jeghers syndrome kinase LKB1 requires its binding to the molecular chaperones Hsp90/Cdc37.

Peutz-Jeghers syndrome (PJS) is an autosomal dominant disorder characterized by the presence of multiple gastrointestinal polyps and an increased risk for various types of cancers. Inactivating germline mutations of the LKB1 gene, which encodes a serine/threonine kinase, are responsible for the majority of PJS cases. Here, we show that the heteromeric complex containing the molecular chaperones Hsp90 and Cdc37/p50 interacts with the kinase domain of LKB1. Treatment of cells with either geldanamycin or novobiocin, two pharmacological inhibitors of Hsp90 causes the destabilization of LKB1. Furthermore, geldanamycin treatment leads to the ubiquitination and the rapid degradation of LKB1 by the proteasome-dependent pathway. In addition, we found that a LKB1 point mutation identified in a sporadic testicular cancer, weakens the interaction of LKB1 with both Hsp90 and Cdc37/p50 and enhances its sensitivity to the destabilizing effect of geldanamycin. Collectively, our results demonstrate that the Hsp90/Cdc37 complex is a major regulator of the stability of the LKB1 tumor suppressor. Furthermore, these data draw attention to the possible adverse consequences of antitumor drugs that target Hsp90, such as antibiotics related to geldanamycin, which could disrupt LKB1 function and promote the development of polyps and carcinomatous lesions.

Evidence for packaging of rep-cap sequences into adeno-associated virus (AAV) type 2 capsids in the absence of inverted terminal repeats: a model for generation of rep-positive AAV particles.

We previously reported that a 350-bp region of the adeno-associated virus (AAV) type 2 rep gene contains a cis-acting element responsible for the Rep-dependent replication of a transiently transfected rep-cap plasmid. In this study, we further report that replicated rep-cap sequences can be packaged into AAV capsids in the absence of the inverted terminal repeats.