Search PubMed⌕ Search

Biomedical subjects

Kenneth L Rock

Publications and source records attributed to Kenneth L Rock.

28 records · Page 2Linked to original sources
PubMed2004

Post-proteasomal antigen processing for major histocompatibility complex class I presentation.

Peptides presented by major histocompatibility complex class I molecules are derived mainly from cytosolic oligopeptides generated by proteasomes during the degradation of intracellular proteins. Proteasomal cleavages generate the final C terminus of these epitopes. Although proteasomes may produce mature epitopes that are eight to ten residues in length, they more often generate N-extended precursors that are too long to bind to major histocompatibility complex class I molecules. Such precursors are trimmed in the cytosol or in the endoplasmic reticulum by aminopeptidases that generate the N terminus of the presented epitope. Peptidases can also destroy epitopes by trimming peptides to below the size needed for presentation. In the cytosol, endopeptidases, especially thimet oligopeptidase, and aminopeptidases degrade many proteasomal products, thereby limiting the supply of many antigenic peptides. Thus, the extent of antigen presentation depends on the balance between several proteolytic processes that may generate or destroy epitopes.

Animals↗
PubMed2003

Molecular identification of a danger signal that alerts the immune system to dying cells.

In infections, microbial components provide signals that alert the immune system to danger and promote the generation of immunity. In the absence of such signals, there is often no immune response or tolerance may develop. This has led to the concept that the immune system responds only to antigens perceived to be associated with a dangerous situation such as infection. Danger signals are thought to act by stimulating dendritic cells to mature so that they can present foreign antigens and stimulate T lymphocytes. Dying mammalian cells have also been found to release danger signals of unknown identity. Here we show that uric acid is a principal endogenous danger signal released from injured cells. Uric acid stimulates dendritic cell maturation and, when co-injected with antigen in vivo, significantly enhances the generation of responses from CD8+ T cells. Eliminating uric acid in vivo inhibits the immune response to antigens associated with injured cells, but not to antigens presented by activated dendritic cells. Our findings provide a molecular link between cell injury and immunity and have important implications for vaccines, autoimmunity and inflammation.

3T3 Cells↗
PubMed2003

A dietary enzyme: alpha-methylacyl-CoA racemase/P504S is overexpressed in colon carcinoma.

Epidemiological studies have shown that consumption of red meat increases the risk of developing colon cancer. An enzyme, alpha-methylacyl CoA racemase (AMACR), also known as P504S, plays an important role in peroxisomal beta-oxidation of branched-chain fatty acids from red meat and dairy products. High expression of AMACR was recently found in prostate cancer. In this study, we investigated expression of AMACR in 242 cases of colonic tumors including 176 colorectal carcinomas, 38 colon adenomas and 28 hyperplastic (non-neoplastic) polyps by immunohistochemical analysis. The mRNA levels of AMACR expression in normal and colon cancer tissues were assessed by real-time PCR. Significant up-regulation of AMACR mRNA was found in colon carcinomas compared to normal tissue. There was very low or no expression of AMACR protein in normal colon, but AMACR was highly expressed in 76 and 75% of well and moderately differentiated colon carcinomas, respectively, and in 79% of adenomas. In contrast, only 4% of hyperplastic polyps expressed AMACR. Since this enzyme is involved in the metabolism of branched-chain fatty acids from beef, milk and dairy products, our results provide important molecular information regarding a possible link between diet and development of colon cancer. AMACR may also serve as a molecular marker for colon cancers and its precursor lesions.

Adenocarcinoma↗
PubMed2003

The cytosolic endopeptidase, thimet oligopeptidase, destroys antigenic peptides and limits the extent of MHC class I antigen presentation.

Most antigenic peptides presented on MHC class I molecules are generated by proteasomes during protein breakdown. It is unknown whether these peptides are protected from destruction by cytosolic peptidases. In cytosolic extracts, most antigenic peptides are degraded by the metalloendopeptidase, thimet oligopeptidase (TOP). We therefore examined whether TOP destroys antigenic peptides in vivo. When TOP was overexpressed in cells, class I presentation of antigenic peptides was reduced. In contrast, TOP overexpression didn't reduce presentation of peptides generated in the endoplasmic reticulum or endosomes. Conversely, preventing TOP expression with siRNA enhanced presentation of antigenic peptides. TOP therefore plays an important role in vivo in degrading peptides released by proteasomes and is a significant factor limiting the extent of antigen presentation.

Animals↗
PubMed2002

An IFN-gamma-induced aminopeptidase in the ER, ERAP1, trims precursors to MHC class I-presented peptides.

Precursors to major histocompatibility complex (MHC) class I-presented peptides with extra NH2-terminal residues can be efficiently trimmed to mature epitopes in the endoplasmic reticulum (ER). Here, we purified from liver microsomes a lumenal, soluble aminopeptidase that removes NH2-terminal residues from many antigenic precursors. It was identified as a metallopeptidase named "adipocyte-derived leucine" or "puromycin-insensitive leucine-specific" aminopeptidase. However, because we localized it to the ER, we propose it be renamed ER-aminopeptidase 1 (ERAP1). ERAP1 is inhibited by agents that block precursor trimming in ER vesicles and although it trimmed NH2-extended precursors, it spared presented peptides of 8 amino acid and less. Like other proteins involved in antigen presentation, ERAP1 is induced by interferon-gamma. When overexpressed in vivo, we found that ERAP1 stimulates the processing and presentation of an antigenic precursor in the ER.

Animals↗
PubMed2002

The ER aminopeptidase ERAP1 enhances or limits antigen presentation by trimming epitopes to 8-9 residues.

Endoplasmic reticulum (ER) aminopeptidase 1 (ERAP1) appears to be specialized to produce peptides presented on class I major histocompatibility complex molecules. We found that purified ERAP1 trimmed peptides that were ten residues or longer, but spared eight-residue peptides. In vivo, ERAP1 enhanced production of an eight-residue ovalbumin epitope from precursors extended on the NH2 terminus that were generated either in the ER or cytosol. Purified ERAP1 also trimmed nearly half the nine-residue peptides tested. By destroying such nine-residue peptides in normal human cells, ERAP1 reduced the overall supply of antigenic peptides. However, after interferon-gamma treatment, which causes proteasomes to produce more NH2-extended antigenic precursors, ERAP1 increased the supply of peptides for MHC class I antigen presentation.

Animals↗
PubMed2002

Cell death releases endogenous adjuvants that selectively enhance immune surveillance of particulate antigens.

We previously reported that cells contain endogenous adjuvants in their cytoplasm that when released markedly augment the generation of CD8 T cell responses. In the present study we found that these cytosolic adjuvants similarly augmented the generation of CD4 T cell responses, and therefore must be affecting a step that is common to the generation of helper and cytotoxic T cell responses. The endogenous adjuvants work differently than a classical bacterial adjuvant, Freund's complete adjuvant. Remarkably, they stimulate the immune response to particulate and cell-associated antigens but not to the same antigens in soluble form. To gain insight into the underlying mechanisms for these effects, we studied the effect of the cytosolic adjuvants on the fate of particulate antigens and antigen-presenting cells (APC) in vivo. Injection of cytosol by itself causes no detectable change in the number or phenotype of APC in draining lymph nodes. However, co-injection of cytosol and fluorescent particles leads to the increased accumulation in the draining lymph node of dendritic cells and macrophages containing phagocytosed particles and expressing high levels of costimulatory molecules. Therefore, cell injury releases cytosolic factors that selectively enhance immune surveillance of particulate antigens released from dying cells by stimulating APC in tissues to acquire these antigens, mature and migrate to lymph nodes. This process will allow the immune system to rapidly detect and respond to viral infections and tumors.

3T3 Cells↗
PubMed2002

Protein degradation and the generation of MHC class I-presented peptides.

Over the past decade there has been considerable progress in understanding how MHC class I-presented peptides are generated. The emerging theme is that the immune system has not evolved its own specialized proteolytic mechanisms but instead utilizes the phylogenetically ancient catabolic pathways that continually turnover proteins in all cells. Three distinct proteolytic steps have now been defined in MHC class I antigen presentation. The first step is the degradation of proteins by the ubiquitin-proteasome pathway into oligopeptides that either are of the correct size for presentation or are extended on their amino-termini. In the second step, aminopeptidases trim N-extended precursors into peptides of the correct length to be presented on class I molecules. The third step involves the destruction of peptides by endo- and exopeptidases, which limits antigen presentation, but is important for preventing the accumulation of peptides and recycling them back to amino acids for protein synthesis or production of energy. The immune system has evolved several components that modify the activity of these ancient pathways in ways that enhance the generation of class I-presented peptides. These include catalytically active subunits of the proteasome, the PA28 proteasome activator, and leucine aminopeptidase, all of which are upregulated by interferon-gamma. In addition to these pathways that operate in all cells, dendritic cells and macrophages can also generate class I-presented peptides from proteins internalized from the extracellular fluids by degrading them in endocytic compartments or transferring them to the cyotosol for degradation by proteasomes.

Animals↗
PubMed2002

The importance of the proteasome and subsequent proteolytic steps in the generation of antigenic peptides.

Three different proteolytic processes have been shown to be important in the generation of antigenic peptides displayed on MHC-class I molecules. The great majority of these peoptides are derived from oligopeptides produced during the degradation of intracellular proteins by the ubiquitin-proteasome pathway. Novel methods were developed to follow this process in vitro. When pure 26S proteasomes degrade the model substrate, ovalbumin, they produce the immunodominant peptide, SIINFEKL, occasionally, but more often an N-extended form of SIINFEKL. Interferon-gamma stimulates antigen presentation in part by inducing new forms of the proteasome that are more efficient in antigen presentation, and in vitro these immunoproteasomes specifically produce more of the N-extended versions of SIINFEKL. In addition, gamma-interferon induces a novel 26S complex containing the 19S and 20S particles and the proteasome activator, PA28, which we show cleaves proteins in distinct ways. In vivo studies established that proteasomal cleavages produce the C-termini of antigenic peptides, but not their N-termini, which can be formed efficiently by aminopeptidases that trim longer proteasomal products to the presented epitopes. gamma-interferon stimulates this trimming process by inducing in the cytosol leucine aminopeptidase and a novel aminopeptidase in the ER. Peptides released by proteasomes, including antigenic peptides, are labile in cytosolic extracts, and most of the longer proteasome products are rapidly cleaved by the cytosolic enzyme, thymet oligopeptidase (TOP). If cells express large amounts of TOP, class I presentation decreases, and if TOP is inhibited, presentation increases. Thus, peptide degradation in the cytosol appears to limit the efficiency of antigen presentation.

Amino Acids↗