Human glioma cell culture: two FCS-free media could be recommended for clinical use in immunotherapy

Immunotherapy, particularly active vaccination, may be developed as an effective and safe treatment modality for malignant gliomas, which continue to have a poor prognosis, despite advances in surgical techniques and adjuvant chemotherapy and radiotherapy. Since no glioma-specific tumor-associated antigens (TAAs) have been discovered, autologous tumor cells or well-established glioma cell lines could be used in future vaccination protocols to induce antitumour immunity against unknown TAAs. One obstacle for clinical use of these tumour cell vaccines is related to foetal calf serum (FCS). Efforts are currently being directed toward developing FCS-free media and serum-free alternatives to culture these cell vaccines. In this study, a medium containing human serum and one serum-free medium (UltraCulture), supplemented or not with epidermal growth factor, were tested on morphology, survival, DNA content and TAA expression of human glioma cell lines and glioma biopsy primary cultures. Their effects were compared on FCS-containing medium. Results show that, whatever the medium used, no significant variations in morphology and survival were observed. Furthermore, human serum-containing medium or UltraCulture preserved at early passage cultures the cell population of interest present in the biopsies before culture. In addition, the expression profile of eight TAAs was similar between these media. These data indicate that human serum-containing medium and UltraCulture serum-free medium could be promising candidates to produce tumour-cell vaccines.     

Caveolin-1 regulates glioblastoma aggressiveness through the control of alpha(5)beta(1) integrin expression and modulates glioblastoma responsiveness to SJ749, an alpha(5)beta(1) integrin antagonist

Caveolin-1 plays a checkpoint function in the regulation of processes often altered in cancer. Although increased expression of caveolin-1 seems to be the norm in the glioma family of malignancies, populations of caveolin-1 positive and negative cells coexist among glioblastoma specimens. As no data are available to date on the contribution of such cells to the phenotype of glioblastoma, we manipulated caveolin-1 in the glioblastoma cell line U87MG. We showed that caveolin-1 plays a critical role in the aggressiveness of glioblastoma. We identified integrins as the main set of genes affected by caveolin-1. We reported here that the phenotypic changes observed after caveolin-1 modulation were mediated by alpha(5)beta(1) integrins. As a consequence of the regulation of alpha(5)beta(1) levels by caveolin-1, the sensitivity of cells to the specific alpha(5)beta(1) integrin antagonist, SJ749, was affected. Mediator of caveolin-1 effects, alpha(5)beta(1) integrin, is also a marker for glioma aggressiveness and an efficient target for the treatment of glioma especially the ones exerting the highest aggressive phenotype.     

RAD51C facilitates checkpoint signaling by promoting CHK2 phosphorylation

The RAD51 paralogues act in the homologous recombination (HR) pathway of DNA repair. Human RAD51C (hRAD51C) participates in branch migration and Holliday junction resolution and thus is important for processing HR intermediates late in the DNA repair process. Evidence for early involvement of RAD51 during DNA repair also exists, but its function in this context is not understood. In this study, we demonstrate that RAD51C accumulates at DNA damage sites concomitantly with the RAD51 recombinase and is retained after RAD51 disassembly, which is consistent with both an early and a late function for RAD51C. RAD51C recruitment depends on ataxia telangiectasia mutated, NBS1, and replication protein A, indicating it functions after DNA end resection but before RAD51 assembly. Furthermore, we find that RAD51C is required for activation of the checkpoint kinase CHK2 and cell cycle arrest in response to DNA damage. This suggests that hRAD51C contributes to the protection of genome integrity by transducing DNA damage signals in addition to engaging the HR machinery.     

Patterns of DNA-Sequence Divergence Between <Emphasis Type="Italic">Drosophila miranda</Emphasis> and <Emphasis Type="Italic">D. pseudoobscura</Emphasis>

Contrary to the classical view, a large amount of non-coding DNA seems to be selectively constrained in Drosophila and other species. Here, using Drosophila miranda BAC sequences and the Drosophila pseudoobscura genome sequence, we aligned coding and non-coding sequences between D. pseudoobscura and D. miranda, and investigated their patterns of evolution. We found two patterns that have previously been observed in comparisons between Drosophila melanogaster and its relatives. First, there is a negative correlation between intron divergence and intron length, suggesting that longer non-coding sequences may contain more regulatory elements than shorter sequences. Our other main finding is a negative correlation between the rate of non-synonymous substitutions (d _N) and codon usage bias (F _op), showing that fast-evolving genes have a lower codon usage bias, consistent with strong positive selection interfering with weak selection for codon usage.     

N-cadherin/p120 Catenin Association at Cell-Cell Contacts Occurs in Cholesterol-rich Membrane Domains and Is Required for RhoA Activation and Myogenesis

p120 catenin is a major regulator of cadherin stability at cell-cell contacts and a modulator of Rho GTPase activities. In C2C12 myoblasts, N-cadherin is stabilized at cell contacts through its association with cholesterol-rich membrane domains or lipid rafts (LR) and acts as an adhesion-activated receptor that activates RhoA, an event required for myogenesis induction. Here, we report that association of p120 catenin with N-cadherin at cell contacts occurs specifically in LR. We demonstrate that interaction of p120 catenin with N-cadherin is required for N-cadherin association with LR and for its stabilization at cell contacts. LR disruption inhibits myogenesis induction and N-cadherin-dependent RhoA activation as does the perturbation of the N-cadherin-p120 catenin complex after p120 catenin knockdown. Finally, we observe an N-cadherin-dependent accumulation of RhoA at phosphatidylinositol 4,5-bisphosphate-enriched cell contacts which is lost after LR disruption. Thus, a functional N-cadherin-catenin complex occurs in cholesterol-rich membrane microdomains which allows the recruitment of RhoA and the regulation of its activity during myogenesis induction.Skeletal myogenesis is a multistep process regulated by diffusible molecules and the interaction of muscle cell precursors with their neighbors and the extracellular matrix (1, 2). Particularly, N-cadherin-dependent intercellular adhesion has a major role in cell cycle exit and induction of skeletal muscle differentiation through activation of the Rho family GTPases. RhoA positively regulates MyoD expression and skeletal muscle differentiation because it is required for serum response factor-mediated activation of several muscle-specific gene promoters (3, 4).Dynamic association of cadherin complexes at the plasma membrane (PM)⁴ is crucial for cadherin-mediated signaling. Their extracellular domain mediates homophilic cell-cell adhesion, whereas the intracellular domain associates with catenins that produce attachment sites for the F-actin cytoskeleton (5–7). The juxtamembrane domain of the cadherin cytoplasmic tail binds to p120 catenin, which regulates cadherin stability at cell contacts and modulates Rho GTPase activities (8–11). Cadherin stability is directly dependent on p120 catenin, and in its absence most cadherins are internalized and often degraded, suggesting that p120 catenin controls cadherin turnover at the cell surface (11, 12). Moreover, mutations in the E-cadherin region that bind to p120 catenin dissociate the E-cadherin-p120 catenin complex and disrupt strong cell adhesion, although interaction with other catenins remains intact (13). Cadherin stability at cell-cell contacts is also regulated by homophilic binding between extracellular domains and association with the F-actin cytoskeleton (14, 15). Association of N-cadherin with cholesterol-enriched microdomains, called lipid rafts (LR), at cell contacts, also stabilizes N-cadherin (16). Because p120 catenin interaction with cadherins and N-cadherin association with LR at cell contact sites are both involved in cadherin stability at cell contact sites, we asked whether p120 catenin association with N-cadherin required LR. We observed that their association occurred specifically in these cholesterol-rich domains. Moreover, using an N-cadherin mutant unable to bind to p120 catenin, we showed that the N-cadherin/p120 catenin interaction was required for N-cadherin association with LR and its stabilization at cell contacts. Because N-cadherin is implicated in the commitment to myogenesis through RhoA activation, we questioned whether its association with p120 catenin in LR was a prerequisite for RhoA activation. LR disruption inhibited myogenesis induction, association of p120 catenin with N-cadherin, and N-cadherin-dependent RhoA activation, as did the perturbation of the N-cadherin-p120 catenin complex after p120 catenin knockdown. Together, these data suggest a crucial role for the N-cadherin/p120 catenin association in LR in the regulation of RhoA activity during myogenesis induction.