a-microscopic-phenotypic-assay-for-quantification-intracellular

A Microscopic Phenotypic Assay for the Quantification of Intracellular Mycobacteria Adapted for High-throughput/High-content Screening

Despite the availability of therapy and vaccine, tuberculosis (TB) remains one of the most deadly and widespread bacterial infections in the world. Since ...

Université de Lille

Patupilone is an epothilone in advanced clinical development that has shown promising efficacy in heavily pretreated patients. This study aimed at characterizing the mechanisms of patupilone activity in resistant patients. To this end, we generated patupilone-resistant cells using two cellular models, the first characterized by high chemosensitivity and low class III beta-tubulin (TUBB3) expression (A2780), and the second by low chemosensitivity and high TUBB3 expression (OVCAR-3). The obtained cell lines were named EPO3 and OVCAR-EPO, respectively. The same selection procedure was done in A2780 cells to generate a paclitaxel-resistant cell line (TAX50). Factors of resistance are expected to increase in the drug-resistant cell lines, whereas factors of drug sensitivity will be down-regulated. Using this approach, we found up-regulation of TUBB3 in TAX50, but not EPO3, cells, showing that TUBB3 mediates the resistance to paclitaxel but not to patupilone. Moreover, TUBB3 was a factor of patupilone sensitivity because OVCAR-EPO cells exhibited a dramatic reduction of TUBB3 and a concomitant sensitization to hypoxia and cisplatin-based chemotherapy. To identify the mechanisms underlying patupilone resistance, tubulin genes were sequenced, thereby revealing that a prominent mechanism of drug resistance is represented by point mutations in class I beta-tubulin. Overall, these results suggest that paclitaxel and patupilone have nonoverlapping mechanisms of resistance, thus allowing the use of patupilone for those patients relapsing after paclitaxel-based chemotherapy. Furthermore, patupilone represents a promising first-line option for the treatment of high-risk ovarian cancer patients, who exhibit high TUBB3 levels and poor response to standard paclitaxel-platin chemotherapy.

Molecular mechanisms of patupilone resistance.

The combinatorial phage display library approach to antibody repertoire cloning offers a powerful tool for the isolation of specific antibodies to defined target antigens. Panning strategy is often a very critical point for selecting antibody displayed on the surface of bacteriophages. Most selection strategies described to date have relied on the availability of purified and often recombinant antigen, providing the possibility to perform selections on a well defined antigen source. However, when the antigen is difficult to purify by means of laborious and time-consuming chromatography procedures, panning of phage antibody libraries has to be performed on complex antigen sources such as cell surfaces or tissue sections, or even by in vivo selection methods. This provides a series of technical and experimental complications. In the present work, we successfully generated a mouse monoclonal antibody fragment from a phage display library directed against protein E7 of HPV18 avoiding antigen purification as for immunizing mice as for antibody library selection. Our work demonstrates the feasibility of phage antibody selections on antigens transferred to a nitrocellulose membrane as solid support, using one-dimensional polyacrylamide gel electrophoresis system as the only practice to separate a given antigen present in bacterial crude cell lysate.

Effective use of nitrocellulose-blotted antigens for phage display monoclonal antibody selection.

The role and function of PE_PGRS proteins of Mycobacterium tuberculosis (Mtb) remains elusive. In this study for the first time, Mtb isogenic mutants missing selected PE_PGRSs were used to investigate their role in the pathogenesis of tuberculosis (TB). We demonstrate that the MtbΔPE_PGRS30 mutant was impaired in its ability to colonize lung tissue and to cause tissue damage, specifically during the chronic steps of infection. Inactivation of PE_PGRS30 resulted in an attenuated phenotype in murine and human macrophages due to the inability of the Mtb mutant to inhibit phagosome-lysosome fusion. Using a series of functional deletion mutants of PE_PGRS30 to complement MtbΔPE_PGRS30, we show that the unique C-terminal domain of the protein is not required for the full virulence. Interestingly, when Mycobacterium smegmatis recombinant strain expressing PE_PGRS30 was used to infect macrophages or mice in vivo, we observed enhanced cytotoxicity and cell death, and this effect was dependent upon the PGRS domain of the protein.Taken together these results indicate that PE_PGRS30 is necessary for the full virulence of Mtb and sufficient to induce cell death in host cells by the otherwise non-pathogenic species M. smegmatis, clearly demonstrating that PE_PGRS30 is an Mtb virulence factor.

PE_PGRS30 is required for the full virulence of Mycobacterium tuberculosis.

PE_PGRSs are a large family of proteins identified in Mycobacterium tuberculosis complex and in few other pathogenic mycobacteria. The PE domain of PE_PGRS33 mediates localization of the protein on the mycobacterial cell surface, where the PGRS domain is available to interact with host components. In this study, PE_PGRS33 and its functional deletion mutants were expressed in M. smegmatis, and in vitro and in vivo assays were used to dissect the protein domains involved in the immunomodulatory properties of the protein. We demonstrate that PE_PGRS33-mediated secretion of TNF-α by macrophages occurs by extracellular interaction with TLR2. Our results also show that while the PGRS domain of the protein is required for triggering TNF-α secretion, mutation in the PE domain affects the pro-inflammatory properties of the protein. These results indicate that PE_PGRS33 is a protein with immunomodulatory activity and that protein stability and localization on the mycobacterial surface can affect these properties.

Article	Year
Molecular mechanisms of patupilone resistance. Cancer research\| PubMed ID: 19074887	2008
Effective use of nitrocellulose-blotted antigens for phage display monoclonal antibody selection. The new microbiologica\| PubMed ID: 21811748	2011
PE_PGRS30 is required for the full virulence of Mycobacterium tuberculosis. Cellular microbiology\| PubMed ID: 22050772	2012
Functional dissection of protein domains involved in the immunomodulatory properties of PE_PGRS33 of Mycobacterium tuberculosis. Pathogens and disease\| PubMed ID: 24106104	2013

Raffaella Iantomasi

Biography

JoVE Journal Publications

Other Publications