Showing papers by "John I. Risinger published in 1999"

Mutations and altered expression of the human cancer genes: what they tell us about causes.

Abstract: To understand the causes of cancer, it is necessary to elucidate the molecular basis and environmental factors that influence the carcinogenesis process. Cancers are progressive diseases characterized by the accumulation of defects in many different genes. The patterns of mutation of some genes identified in tumours suggest a direct action of chemicals binding to and altering DNA. Other cancer-associated genes may be altered as a consequence of endogenous mutagens, germ-line mutations, spontaneous mutations that occur during cell replication or increased genetic instability in precancerous cells. Recent advances in molecular biology and genetics have provided new tools and concepts for studying the causes of cancer. We know that cancers are caused by a combination of environmental and genetic factors, and the discovery of the molecular alterations that occur at various stages in different tumours is increasing our understanding of these causes. Thus, we are now beginning to discover which genes are involved, how they function normally and in tumour tissues and why cancers develop after a series of genetic and epigenetic changes in certain cells. As data from studies on cancer-associated genes have accrued, the categories of genes and molecular pathways that have been found to play a role in carcinogenesis have also increased. Genes involved in development and other normal cellular processes have been implicated in cancer. These include genes involved in signal transduction, cell cycle control, DNA repair, cell growth and differentiation (growth factors and growth factor receptors), transcriptional regulation, senescence and apoptosis. Genes involved in angiogenesis, immune regulation, cellular responses to stress, motility, adhesion and invasion are also involved, but less is known about their relationship to carcinogenesis, and these processes are not discussed in this review. The diverse nature of these categories of cancer-related genes indicates the variety of processes that must be disrupted in order for tumours to develop. Many of the genes have several functional domains, and the functions of some have only recently been proposed. In this review, we describe some of the major classes of genes implicated in human cancers and some of the major findings on genetic alterations and dysfunction in human tumours. Comparisons are made with certain rodent models.

The linoleic acid metabolite, 13-HpODE augments the phosphorylation of EGF receptor and SHP-2 leading to their increased association.

Abstract: In previous studies with Syrian hamster embryo fibroblasts, we found that a specific lipoxygenase metabolite of linoleic acid, 13(S)-hydroperoxyoctadecadienoic acid (HpODE), enhanced epidermal growth factor (EGF) signal transduction in a tumor suppressor gene plus phenotype (supB+); with a diminished response to 13(S)-HpODE in a tumor suppressor gene minus phenotype (supB-). This differential response was attributed to differences in the rate of EGF receptor (EGFR) dephosphorylation. To further define the molecular basis for these observations, in this report we examine the interaction of phosphorylated EGFR with the SH2 domain-containing protein tyrosine phosphatase, SHP-2, a positive modulator of EGF dependent cell growth. SHP-2 associated with phosphorylated EGFR to a greater extent in supB+ cells when compared to supB-. This differential association could not be accounted for by differences between suppressor gene phenotypes in SHP-2 protein level or mutations in the molecular sequence. The addition of 13(S)-HpODE stimulated a concentration-dependent increase in EGF-dependent phosphorylation of SHP-2 and its association with EGFR. A more dramatic response was observed in the supB+ cells. Differences in SHP-2 interaction with EGFR may account, in part, for phenotypic differences in the growth rates and responsiveness to EGF between the supB+ and supB- cells. EGFR-SHP-2 association appears to play an important role in the regulation of EGFR signal transduction.