Phosphoglycerate dehydrogenase diverts glycolytic flux and contributes to oncogenesis

Most tumors exhibit increased glucose metabolism to lactate, however, the extent to which glucose-derived metabolic fluxes are used for alternative processes is poorly understood. Using a metabolomics approach with isotope labeling, we found that in some cancer cells a relatively large amount of glycolytic carbon is diverted into serine and glycine metabolism through phosphoglycerate dehydrogenase (PHGDH). An analysis of human cancers showed that PHGDH is recurrently amplified in a genomic region of focal copy number gain most commonly found in melanoma. Decreasing PHGDH expression impaired proliferation in amplified cell lines. Increased expression was also associated with breast cancer subtypes, and ectopic expression of PHGDH in mammary epithelial cells disrupted acinar morphogenesis and induced other phenotypic alterations that may predispose cells to transformation. Our findings show that the diversion of glycolytic flux into a specific alternate pathway can be selected during tumor development and may contribute to the pathogenesis of human cancer.     

Association of the Shc and Grb2/Sem5 SH2-containing proteins is implicated in activation of the Ras pathway by tyrosine kinases.

The mammalian shc gene encodes two overlapping, widely expressed proteins of 46 and 52K, with a carboxy-terminal SH2 domain that binds activated growth factor receptors, and a more amino-terminal glycine/proline-rich region. These shc gene products (Shc) are transforming when overexpressed in fibroblasts. Shc proteins become phosphorylated on tyrosine in cells stimulated with a variety of growth factors, and in cells transformed by v-src (ref. 2), suggesting that they are tyrosine kinase targets that control a mitogenic signalling pathway. Here we report that tyrosine-phosphorylated Shc proteins form a specific complex with a non-phosphorylated 23K polypeptide encoded by the grb2/sem-5 gene. The grb2/sem-5 gene product itself contains an SH2 domain, which mediates binding to Shc, and is implicated in activation of the Ras guanine nucleotide-binding protein by tyrosine kinases in both Caenorhabditis elegans and mammalian cells. Consistent with a role in signalling through Ras, shc overexpression induced Ras-dependent neurite outgrowth in PC12 cells. These results suggest that Shc tyrosine phosphorylation can couple tyrosine kinases to Grb2/Sem-5, through formation of a Shc-Grb2/Sem-5 complex, and thereby regulate the mammalian Ras signalling pathway.     

Common effector processing mediates cell-specific responses to stimuli

The fundamental components of many signalling pathways are common to all cells. However, stimulating or perturbing the intracellular network often causes distinct phenotypes that are specific to a given cell type. This 'cell specificity' presents a challenge in understanding how intracellular networks regulate cell behaviour and an obstacle to developing drugs that treat signalling dysfunctions. Here we apply a systems-modelling approach to investigate how cell-specific signalling events are integrated through effector proteins to cause cell-specific outcomes. We focus on the synergy between tumour necrosis factor and an adenoviral vector as a therapeutically relevant stimulus that induces cell-specific responses. By constructing models that estimate how kinase-signalling events are processed into phenotypes through effector substrates, we find that accurate predictions of cell specificity are possible when different cell types share a common 'effector-processing' mechanism. Partial-least-squares regression models based on common effector processing accurately predict cell-specific apoptosis, chemokine release, gene induction, and drug sensitivity across divergent epithelial cell lines. We conclude that cell specificity originates from the differential activation of kinases and other upstream transducers, which together enable different cell types to use common effectors to generate diverse outcomes. The common processing of network signals by downstream effectors points towards an important cell biological principle, which can be applied to the understanding of cell-specific responses to targeted drug therapies.     

The src gene product of transformed and morphologically reverted ASV-infected mammalian cells.

Morphological revertants of avian sarcoma virus transformed vole cells contain the sarcoma gene product (pp60src) in an enzymatically active form, suggesting that the presence of pp60src protein kinase activity is infussicient to induce morphological transformation. Structural analyses of pp60src from infected vole cell clones suggest that in one of the revertant clones on alteration in pp60src may be responsible for morphological reversion while in a second clone, reversion may result from an alteration in a cell gene product with which pp60src must interact. As these morphological revertant cells are tumorigenic, different cell components are required to interact with pp60src to facilitate the two events.     

Neurones express high levels of a structurally modified, activated form of pp60c-src

Neural tissues contain high levels of the cellular homologue of the transforming protein of Rous sarcoma virus (RSV), but neither the specific cell types expressing high levels of c-src, nor the function of the cellular src (c-src) protein has been determined. Using primary culture methods, we have found that pure neurones and astrocytes derived from the rat central nervous system (CNS) contain 15- to 20-times higher levels of the c-src protein than fibroblasts. However, the specific activity of the c-src protein from the neuronal cultures is 6- to 12-times higher than that from the astrocyte cultures. In addition, the c-src protein expressed in neuronal cultures contains a structural alteration within the amino-terminal region of the molecule that causes a shift in the mobility of the c-src protein on the SDS-polyacrylamide gels. These results indicate that a structurally distinct form of the cellular src protein that possesses an activated tyrosylkinase activity is expressed at very high levels in post-mitotic CNS neurones.     

Overview of the Alliance for Cellular Signaling

The Alliance for Cellular Signaling is a large-scale collaboration designed to answer global questions about signalling networks. Pathways will be studied intensively in two cells--B lymphocytes (the cells of the immune system) and cardiac myocytes--to facilitate quantitative modelling. One goal is to catalyse complementary research in individual laboratories; to facilitate this, all alliance data are freely available for use by the entire research community.