Current Molecular Medicine - Volume 3, Issue 1, 2003

Many autoimmune diseases have genetic associations with the Major Histocompatibility Complex (MHC) class II loci. Susceptibility to Type 1 diabetes mellitus (TIDM) is particularly associated with Human Leucocyte Antigen (HLA) DR3, 4 and associated DQ2, 8 alleles and this is well documented in genetic association studies. These molecules play an important role in presentation of peptide antigens after intracellular processing to CD4 T lymphocytes. During the last decade, a number of approaches have been used to elucidate the molecular basis for the association of particular alleles with susceptibility to or protection from TIDM. These studies have focused on investigating the structure of the antigen presenting molecules, together with their peptides. Through binding studies, peptide elution, molecular modelling and crystallization of the peptide MHC complex, it has been possible to define the peptide binding regions and examine the stability of binding of peptides from putative autoantigens. This knowledge has also facilitated the development of reagents such as multimeric MHC-peptide complexes that will help to track the low frequency, potentially pathogenic antigen specific cells. Recently, HLA transgenic mice have been generated and used to study T cell epitopes. In addition, although it is clear that the presence of HLA molecules alone does not by itself cause disease, these transgenic mice will develop diabetes when there is an islet “insult”, even if the islet “insult” is, itself, not sufficient to precipitate disease in the absence of the HLA class II transgene. These mice will allow further study of the role of these HLA molecules in vivo. We now have a much greater general understanding of the possible reasons why particular molecules may encode susceptibility to or protection from disease. All these studies will provide information to ultimately define a rational basis for the development of targeted immunotherapy.

α-synuclein is a recently discovered protein that was first identified as the major non amyloid component of senile plaques, the cerebral lesion likely responsible for Alzheimer's disease. The role of α-synuclein in another brain disease namely Parkinson's disease, has been more deeply documented. It appears that α-synuclein fills up the intracytoplasmic inclusions called Lewy bodies that likely contribute to the etiology of Parkinson's disease. Furthermore, rare familial forms of Parkinson's disease have been shown to be linked to autosomal dominant mutations of α-synucleins. Is α-synuclein a bridge between Alzheimer's and Parkinson's diseases? Could it be seen as a common denominator for these two neurodegenerative diseases? These issues could be better addressed by further delineating the physiological function of α-synuclein and, as a corollary, the dysfunction taking place along with the diseases. Here, I will review the recent advances concerning the physiology of α-synuclein and will particularly focus on the post-traductional events leading to drastic biophysical transformations. I will describe recent works suggesting that these modifications directly modulate the normal function of α-synuclein, likely accounting for the dysfunction associated with Parkinson's disease and perhaps contributing to Alzheimer's pathology.

Proteins in general and secretory proteins in particular undergo posttranslational processes before they reach the structure in which they can fulfill their functional purpose. The protein precursor may undergo a wide variety of proteolytic cleavages, N- and C-terminal trimmings and amino acid derivatizations in cells that express the protein. Occasionally, the same precursor is differently processed in different cell types and, in addition, diseased cells may process a given precursor abnormally. For instance, the translational process is often either increased or decreased in diseased cells, which render the ensuing modifications of the precursor incomplete. As a result, a variable mixture of precursors and processing-intermediates accumulates. Measurement of a single protein or peptide component of the posttranslational processing cascade may not facilitate the diagnosis of a disease, because the pattern of precursors and processing products vary individually among patients.In order to exploit disturbed posttranslational processing for diagnostic use, and - at the same time - provide an accurate measure of the translational product, a simple analytical principle named “processing-independent analysis” (PIA) has been designed. PIA-methods quantitate the total mRNA product irrespective of the degree of precursor processing. PIA-methods have recently been developed for a number of prohormones and neuroendocrine proteins, and their diagnostic potential appears promising in early diagnosis of tumors and cardiovascular diseases.The present review describes posttranslational processing patterns for some neuroendocrine proteins. Second, PIA-measurements of precursor-products are mentioned with indication of problems and pitfalls. Finally, PIA-results obtained in diagnosis of neoplastic and cardiovascular diseases are highlighted. But first general aspects of the posttranslational processing are reviewed as a necessary basis for the understanding of the new diagnostic possibilities.

Genes which encode inflammatory cytokines are subject to polymorphisms in their regulatory regions that may effect both the level and ratio of cytokines produced in response to exogenous stimuli. These variant alleles are observed in a large percent of the population and are often associated with increased or decreased susceptibility or severity (modifiers) to infectious, immune or inflammatory diseases. Environmental factors can also play either a direct (i.e., causative factor) or indirect (modifying factor) role in these diseases. Thus, it would follow that gene-environment interactions would effect the expression and / or progression of the disease. In the present review, the concept that some of the common allelic variants found in cytokine genes represent modifying factors in chronic inflammatory diseases associated with occupational exposure is discussed.

Now, at the beginning of a new century, 80 years after Warburg's Nobel prize winning discoveries, we are beginning to make sense of the underlying causes of the well known metabolic phenotype of tumor cells. Building on decades of research to understand the interrelationships between respiration and glycolysis in cancer, the tumor metabolic phenotype can now begin to be understood in a genomic context. With the discovery of hypoxia inducible factor-1 (HIF-1), which is widely overexpressed across a broad range of cancers, modern molecular tools have allowed us to put together the pattern of events that might explain the metabolic differences between tumor and normal cells. HIF-1 controls cellular and systemic responses to oxygen availability and coordinates upregulation of genes involved in many pathways concerned with tumour growth and metabolism including angiogenesis, glucose and energy metabolism, cellular proliferation, differentiation and viability, apoptosis, pH regulation and matrix metabolism. These findings begin to explain how glucose uptake and glycolysis could be up-regulated in cancer cells (through binding to a core DNA recognition sequence) in a co-ordinated and constitutive fashion that may also allow us to elucidate new targets for tumor therapy.

The goal of oncolytic therapy is to exploit the innate ability of viruses to infect tumor cells, replicate in tumor cells, and produce selective oncolysis while sparing normal cells. Although the concept that viruses can be oncolytic is not new, it is only in the last three decades that efforts have been directed at genetically mutating viruses to specifically target characteristics of cancer cells. Several viruses have the potential to infect, replicate and lyse tumor cells, each taking advantage of different host cancer cell biology. This review will focus on the major viruses under current investigation for oncolytic therapy, the mechanism by which they specifically eradicate tumors, and the clinical strategies currently under investigation.

The astrocytomas represent the most common primary tumors of the brain. Despite efforts to improve the treatment of astrocytomas, these tumors and in particular the high-grade astrocytoma termed glioblastoma multiforme still carry a poor prognosis. In recent years, there has been an intensive effort to gain an understanding of the cellular and molecular mechanisms that contribute to the pathogenesis of astrocytomas as a first step toward the development of better treatments for these devastating tumors. Here, we will review our current understanding of the signaling pathways that underlie glial transformation. Studies of astrocytomas have led to the identification of two major groups of signaling proteins whose abnormalities contribute to gliomagenesis: the cell cycle pathways and the growth factor-regulated signaling pathways. Among the cell cycle proteins, the p16-cdk4-pRb and ARF-MDM2-p53 cell cycle arrest pathways play a prominent role in glial transformation. In addition, deregulation of polypeptide growth factors acting via receptor tyrosine kinases (RTKs) and of intracellular signals, including the lipid phosphatase PTEN, that regulate cellular responses to RTKs plays a critical role in gliomagenesis. In addition to the identification of the signaling proteins targeted in glial transformation, the cell-of-origin of astrocytomas has been investigated. Genetic modeling of astrocytomas in mice suggests that neuroepithelial precursor cells represent preferred cellular substrates of gliomas or that either astrocytes or precursor cells constitute potential cells-of-origin of astrocytomas. During normal brain development, neuroepithelial precursor cells, including neural stem cells, differentiate into astrocytes. As the mechanisms that control gliogenesis during normal brain development become better understood, it will be important to determine if deregulation of these mechanisms might contribute to the pathogenesis of astrocytomas. The elucidation of the molecular underpinnings of astrocytomas holds the promise of improved treatment options for patients with these devastating brain tumors.

Mast cells function as the initiator of the allergic reaction and play a role in the innate immune system. Aggregation of the high affinity IgE receptor (FcεRI) on mast cells triggers degranulation with the release of chemical mediators such as histamine, production of cytokines and leukotrienes. FcεRI signals by activating proximal non-receptor type of protein-tyrosine kinases, Lyn, Syk, Btk and Fyn. Activated tyrosine kinases then phosphorylate their specific substrates which include other enzymes and adaptor proteins and assemble these cytoplasmic signaling molecules for cellular activation. The adaptor proteins have multiple domains that allow binding to effector molecules and therefore act as positive or negative regulators controlling FcεRI signaling. Deletion of the adaptor proteins such as LAT, SLP-76 or Gab2 resulted in decreased FcεRI-mediated anaphylactic reaction in vivo. Functional analysis of adaptor proteins has raised the possibility that they may be new targets for the discovery of anti-allergic drugs.