Activation induced deaminase: the importance of being specific

Activation-induced deaminase (AID) is required for class switch recombination and somatic hypermutation in immunoglobulin genes. Although the preponderance of evidence suggests that AID functions by deaminating deoxycytidine in DNA, the question remains whether it can also deaminate cytidine in mRNA, as originally proposed based on its homology to RNA-editing enzymes. Recently, the biological relevance of assaying mammalian enzymes for DNA deaminase activity using Escherichia coli DNA as a reporter has been questioned, representing another round in the ongoing debate.     

Disassociation of met-mediated biological responses in vivo: the natural hepatocyte growth factor/scatter factor splice variant NK2 antagonizes growth but facilitates metastasis

Hepatocyte growth factor/scatter factor (HGF/SF) stimulates numerous cellular activities capable of contributing to the metastatic phenotype, including growth, motility, invasiveness, and morphogenetic transformation. When inappropriately expressed in vivo, an HGF/SF transgene induces numerous hyperplastic and neoplastic lesions. NK1 and NK2 are natural splice variants of HGF/SF; all interact with a common receptor, Met. Although both agonistic and antagonistic properties have been ascribed to each isoform in vitro, NK1 retains the full spectrum of HGF/SF-like activities when expressed as a transgene in vivo. Here we report that transgenic mice broadly expressing NK2 exhibit none of the phenotypes characteristic of HGF/SF or NK1 transgenic mice. Instead, when coexpressed in NK2-HGF/SF bitransgenic mice, NK2 antagonizes the pathological consequences of HGF/SF and discourages the subcutaneous growth of transplanted Met-containing melanoma cells. Remarkably, the metastatic efficiency of these same melanoma cells is dramatically enhanced in NK2 transgenic host mice relative to wild-type recipients, rivaling levels achieved in HGF/SF and NK1 transgenic hosts. Considered in conjunction with reports that in vitro NK2 induces scatter, but not other activities, these data strongly suggest that cellular motility is a critical determinant of metastasis. Moreover, our results demonstrate how alternatively structured ligands can be exploited in vivo to functionally dissociate Met-mediated activities and their downstream pathways.     

Hereditary papillary renal carcinoma type I

Germline missense mutations in the tyrosine kinase domain of the hepatocyte growth factor/scatter factor (HGF/SF) receptor, c-Met, are thought to be responsible for hereditary papillary renal carcinoma (HPRC) type 1, a form of human kidney cancer. In addition to extensive linkage analysis of HPRC families localizing the HPRC type 1 gene within chromosome 7, the demonstration that individual c-Met mutations reconstituted in cultured cells display enhanced and dysregulated kinase activity, and confer cell transformation and tumorigenicity in mice, solidifies this conclusion. Our prior knowledge of HGF/SF biology and c-Met signaling enabled rapid progress in unraveling the molecular pathogenesis of HPRC type 1, and in laying the framework for the development of novel therapeutics for the treatment of this cancer. At the same time, the study of HPRC type 1 has refined our appreciation of the oncogenic potential of c-Met signaling, and challenges our current understanding of HGF/SF and c-Met function in health and disease.     

On the infusion of a therapeutic agent into a solid tumor modeled as a poroelastic medium

The direct infusion of an agent into a solid tumor, modeled as a spherical poroelastic material with anisotropic dependence of the tumor hydraulic conductivity upon the tissue deformation, is treated both by solving the coupled fluid/elastic equations, and by expressing the solution as an asymptotic expansion in terms of a small parameter, ratio between the driving pressure force in the fluid system, and the elastic properties of the solid. Results at order one match almost perfectly the solutions of the full system over a large range of infusion pressures. Comparison with experimental results is acceptable after the hydraulic conductivity of the medium is properly calibrated. Given the uncertain estimates of some model constants, the order zero solution of the expansion, for which fluid and porous matrix are decoupled, yields acceptable values and trends for all the physical fields of interest, rendering the coupled analysis (in the limit of small displacements) of little use. When the deformation of the tissue becomes large nonlinear elasticity theory must be resorted to.     

Utilization of a nitrobenzoxadiazole (NBD) fluorophore in the design of a Grb2 SH2 domain-binding peptide mimetic

Fluorescence labeling has become a general technique for studying the intracellular accumulation and localization of exogenously administered materials. Reported herein is a low nanomolar affinity Grb2 SH2 domain-binding antagonist that utilizes the environmentally-sensitive nitrobenzoxadiazole (NBD) fluorophore as a naphthyl replacement. This novel agent should serve as a useful tool to visualize the actions of this class of Grb2 SH2 domain-binding antagonists in whole cell systems.     

Primate immunoglobulin heavy chain constant gamma genes: an hypothesis of their evolution

Four Immunoglobulin gamma heavy chain isotypes are present in humans; the true phylogenetic relationship between the genes are not known because of the complex concerted evolution of the Ig multigene locus. Here we present data obtained from Southern blot analysis of the gamma genes in several primate species including prosimians (Lemur catta), New World Monkeys (Saguinus oedipus) and Old World Monkeys (Cercopitecus aethiops andMacaca fascicularis). Our data show the presence of a single IgG gene inLemur and probably inS.l oedipus, and of multiple genes in the two Cercopithecinae. These findings suggest that a single IgG gene was present in the ancestor of primates: we suppose that this IgG gene was later duplicated several times during primate evolution.