Biomedical subjects

Alexander Griekspoor

Publications and source records attributed to Alexander Griekspoor.

7 recordsLinked to original sources

PubMed2006

Radiation modulates the peptide repertoire, enhances MHC class I expression, and induces successful antitumor immunotherapy.

Radiotherapy is one of the most successful cancer therapies. Here the effect of irradiation on antigen presentation by MHC class I molecules was studied. Cell surface expression of MHC class I molecules was increased for many days in a radiation dose-dependent manner as a consequence of three responses. Initially, enhanced degradation of existing proteins occurred which resulted in an increased intracellular peptide pool. Subsequently, enhanced translation due to activation of the mammalian target of rapamycin pathway resulted in increased peptide production, antigen presentation, as well as cytotoxic T lymphocyte recognition of irradiated cells. In addition, novel proteins were made in response to gamma-irradiation, resulting in new peptides presented by MHC class I molecules, which were recognized by cytotoxic T cells. We show that immunotherapy is successful in eradicating a murine colon adenocarcinoma only when preceded by radiotherapy of the tumor tissue. Our findings indicate that directed radiotherapy can improve the efficacy of tumor immunotherapy.

Adenocarcinoma↗

PubMed2006

A genetic screen implicates miRNA-372 and miRNA-373 as oncogenes in testicular germ cell tumors.

Endogenous small RNAs (miRNAs) regulate gene expression by mechanisms conserved across metazoans. While the number of verified human miRNAs is still expanding, only few have been functionally annotated. To perform genetic screens for novel functions of miRNAs, we developed a library of vectors expressing the majority of cloned human miRNAs and created corresponding DNA barcode arrays. In a screen for miRNAs that cooperate with oncogenes in cellular transformation, we identified miR-372 and miR-373, each permitting proliferation and tumorigenesis of primary human cells that harbor both oncogenic RAS and active wild-type p53. These miRNAs neutralize p53-mediated CDK inhibition, possibly through direct inhibition of the expression of the tumor-suppressor LATS2. We provide evidence that these miRNAs are potential novel oncogenes participating in the development of human testicular germ cell tumors by numbing the p53 pathway, thus allowing tumorigenic growth in the presence of wild-type p53.

Cells, Cultured↗

PubMed2005

Spatial separation of HLA-DM/HLA-DR interactions within MIIC and phagosome-induced immune escape.

Major Histocompatibility Complex (MHC) class II molecules, including Human Leukocyte Antigen (HLA)-DR, present peptide fragments from proteins degraded in the endocytic pathway. HLA-DR is targeted to late-endocytic structures named MHC class II-containing Compartments (MIIC), where it interacts with HLA-DM. This chaperone stabilizes HLA-DR during peptide exchange and is critical for successful peptide loading. To follow this process in living cells, we have generated cells containing HLA-DR3/Cyan Fluorescent Protein (CFP), HLA-DM/Yellow Fluorescent Protein (YFP), and invariant chain. HLA-DR/DM interactions were observed by Fluorescence Resonance Energy Transfer (FRET). These interactions were pH insensitive, yet occurred only in internal structures and not at the limiting membrane of MIIC. In a cellular model of infection, phagosomes formed a limiting membrane surrounding internalized Salmonella. HLA-DR and HLA-DM did not interact in Salmonella-induced vacuoles, and HLA-DR was not loaded with antigens. The absence of HLA-DR/DM interactions at the limiting membrane prevents local loading of MHC class II molecules in phagosomes. This may allow these bacteria to successfully evade the immune system.

Cell Line↗

PubMed2005

Presenting antigen presentation in living cells using biophysical techniques.

The combination of genetically encoded fluorescent probes and advanced microscopic techniques has dramatically propelled the understanding of cell biology. Highly complex reactions can now be studied in detail in a relatively cost-effective and easy manner and, perhaps most importantly, in the context of a single living cell. In the past decade, numerous reports have uncovered the localization of key molecules in virtually all cellular processes. However, there remains a need for more accurate determination of genuine protein-protein interactions and quantification of highly dynamic processes, which has resulted in the revival of several biophysical techniques. Recent applications of these techniques have deepened understanding of processes involved in antigen presentation to the immune system.

Antigen Presentation↗

PubMed2005

Chaperoning antigen presentation by MHC class II molecules and their role in oncogenesis.

Tumor vaccine development aimed at stimulating the cellular immune response focuses mainly on MHC class I molecules. This is not surprising since most tumors do not express MHC class II or CD1 molecules. Nevertheless, the most successful targets for cancer immunotherapy, leukemia and melanoma, often do express MHC class II molecules, which leaves no obvious reason to ignore MHC class II molecules as a mediator in anticancer immune therapy. We review the current state of knowledge on the process of MHC class II-restricted antigen presentation and subsequently discuss the consequences of MHC class II expression on tumor surveillance and the induction of an efficient MHC class II mediated antitumor response in vivo and after vaccination.

Antigen Presentation↗

PubMed2004

Tamoxifen resistance by a conformational arrest of the estrogen receptor alpha after PKA activation in breast cancer.

Using a novel approach that detects changes in the conformation of ERalpha, we studied the efficacy of anti-estrogens to inactivate ERalpha under different experimental conditions. We show that phosphorylation of serine-305 in the hinge region of ERalpha by protein kinase A (PKA) induced resistance to tamoxifen. Tamoxifen bound but then failed to induce the inactive conformation, invoking ERalpha-dependent transactivation instead. PKA activity thus induces a switch from antagonistic to agonistic effects of tamoxifen on ERalpha. In clinical samples, we found that downregulation of a negative regulator of PKA, PKA-RIalpha, was associated with tamoxifen resistance prior to treatment. Activation of PKA by downregulation of PKA-RIalpha converts tamoxifen from an ERalpha inhibitor into a growth stimulator, without any effect on ICI 182780 (Fulvestrant).

Antineoplastic Agents, Hormonal↗

PubMed2003

Peptide diffusion, protection, and degradation in nuclear and cytoplasmic compartments before antigen presentation by MHC class I.

Antigenic peptides generated by the proteasome have to survive a peptidase-containing environment for presentation by MHC class I molecules. We have visualized the fate and dynamics of intracellular peptides in living cells. We show that peptides are distributed over two different but interconnected compartments, the cytoplasm and the nucleus, and diffuse rapidly through and between these compartments. Since TAP is excluded from the nuclear face of the nuclear envelope, nuclear peptides have to leave the nucleus to contact TAP. Thereby, these peptides encounter cytosolic peptidases that degrade peptides within seconds unless bound to chromatin. Since peptide degradation is far more efficient than translocation, many peptides will be lost for antigen presentation by MHC class I molecules.

ATP-Binding Cassette Transporters↗