hSpry2 Is Targeted to the Ubiquitin-Dependent Proteasome Pathway by c-Cbl

AbstractSprouty was originally identified in a genetic screen in Drosophila as an antagonist of fibroblast (FGF) and epidermal growth factor (EGF) signaling [1, 2]. Subsequently, four vertebrate homologs were discovered; among these, the human homolog Sprouty 2 (hSpry2) contains the highest degree of sequence homology to the Drosophila protein [3, 4]. It has been shown that hSpry2 interacts directly with c-Cbl, an E3-ubiquitin ligase, which promotes the downregulation of receptor tyrosine kinases (RTKs) [5]. In this study, we have investigated the functional consequences of the association between hSpry2 and c-Cbl. We have found that hSpry2 is ubiquitinated by c-Cbl in an EGF-dependent manner. EGF stimulation induces the tyrosine phosphorylation of hSpry2, which in turn enhances the interaction of hSpry2 with c-Cbl. The c-Cbl-mediated ubiquitination of hSpry2 targets the protein for degradation by the 26S proteasome. An enhanced proteolytic degradation of hSpry2 is also observed in response to FGF stimulation. The FGF-induced degradation of hSpry2 limits the duration of the inhibitory effect of hSpry2 on extracellular signal-regulated kinase (ERK) activation and enables the cells to recover their sensitivity to FGF stimulation. Our results indicate that the interaction of hSpry2 with c-Cbl might serve as a mechanism for the downregulation of hSpry2 during receptor tyrosine kinase signaling

Direct evidence for cancer-cell-autonomous extracellular protein catabolism in pancreatic tumors

Mammalian tissues rely on a variety of nutrients to support their physiological functions. It is known that altered metabolism is involved in the pathogenesis of cancer, but which nutrients support the inappropriate growth of intact malignant tumors is incompletely understood. Amino acids are essential nutrients for many cancer cells that can be obtained through the scavenging and catabolism of extracellular protein via macropinocytosis. In particular, macropinocytosis can be a nutrient source for pancreatic cancer cells, but it is not fully understood how the tumor environment influences metabolic phenotypes and whether macropinocytosis supports the maintenance of amino acid levels within pancreatic tumors. Here we utilize miniaturized plasma exchange to deliver labeled albumin to tissues in live mice, and we demonstrate that breakdown of albumin contributes to the supply of free amino acids in pancreatic tumors. We also deliver albumin directly into tumors using an implantable microdevice, which was adapted and modified from ref. 9. Following implantation, we directly observe protein catabolism and macropinocytosis in situ by pancreatic cancer cells, but not by adjacent, non-cancerous pancreatic tissue. In addition, we find that intratumoral inhibition of macropinocytosis decreases amino acid levels. Taken together, these data suggest that pancreatic cancer cells consume extracellular protein, including albumin, and that this consumption serves as an important source of amino acids for pancreatic cancer cells in vivo.National Science Foundation (U.S.) (Grant T32GM007287)National Cancer Institute (U.S.) (Grant F30CA183474)National Institute of General Medical Sciences (U.S.) (Award T32GM007753)National Institutes of Health (U.S.) (Grant P30CA1405141)National Institutes of Health (U.S.) (Grant R01CA168653

ras proteins: biological effects and biochemical targets (review)

Ras genes are an ubiquitous eukaryotic gene family. Since their discovery as the cellular homologues of the transforming genes of Harvey and Kirsten retroviruses, ras genes have been presumed to play a role in growth control, mainly because of their potential to induce uncontrolled cell proliferation. This notion is strongly supported by recent evidence indicating that ras mutations may be causative or closely linked to the onset of some types of human tumors. However, the mechanism of action of ras proteins in mammalian cells is poorly understood. Using the microinjection technique as a biological assay for ras proteins, it has been possible to address several important questions concerning cellular and biochemical aspects of ras function. When introduced into living cells by microinjection, purified ras proteins can induce cell proliferation, neuronal differentiation, oocyte maturation, and exocytotic degranulation. On the biochemical level, microinjection studies indicated that ras proteins can induce specific alterations in phospholipid metabolism

Simulating Heterogeneous Tumor Cell Populations

<div><p>Certain tumor phenomena, like metabolic heterogeneity and local stable regions of chronic hypoxia, signify a tumor’s resistance to therapy. Although recent research has shed light on the <i>intracellular</i> mechanisms of cancer metabolic reprogramming, little is known about how <i>tumors</i> become metabolically heterogeneous or chronically hypoxic, namely the initial conditions and spatiotemporal dynamics that drive these cell population conditions. To study these aspects, we developed a minimal, spatially-resolved simulation framework for modeling tissue-scale mixed populations of cells based on diffusible particles the cells consume and release, the concentrations of which determine their behavior in arbitrarily complex ways, and on stochastic reproduction. We simulate cell populations that self-sort to facilitate metabolic symbiosis, that grow according to tumor-stroma signaling patterns, and that give rise to stable local regions of chronic hypoxia near blood vessels. We raise two novel questions in the context of these results: (1) How will two metabolically symbiotic cell subpopulations self-sort in the presence of glucose, oxygen, and lactate gradients? We observe a robust pattern of alternating striations. (2) What is the proper time scale to observe stable local regions of chronic hypoxia? We observe the stability is a function of the balance of three factors related to <i>O</i>₂—diffusion rate, local vessel release rate, and viable and hypoxic tumor cell consumption rate. We anticipate our simulation framework will help researchers design better experiments and generate novel hypotheses to better understand dynamic, emergent whole-tumor behavior.</p></div

Release rate for of particle type by cell type.

<p>Release rate for of particle type by cell type.</p

Release rate for of particle type by cell type.

<p>Release rate for of particle type by cell type.</p