Hypoxia is a state of low oxygen availability that limits tumor growth. The mechanism of protein synthesis inhibition by hypoxia and its circumvention by transformation are not well understood. Hypoxic breast epithelial cells are shown to downregulate protein synthesis by inhibition of the kinase mTOR, which suppresses mRNA translation through a novel mechanism mitigated in transformed cells: disruption of proteasome-targeted degradation of eukaryotic elongation factor 2 (eEF2) kinase and activation of the regulatory protein 4E-BP1. In transformed breast epithelial cells under hypoxia, the mTOR and S6 kinases are constitutively activated and the mTOR negative regulator tuberous sclerosis complex 2 (TSC2) protein fails to function. Gene silencing of 4E-BP1 and eEF2 kinase or TSC2 confers resistance to hypoxia inhibition of protein synthesis in immortalized breast epithelial cells. Breast cancer cells therefore acquire resistance to hypoxia by uncoupling oxygen-responsive signaling pathways from mTOR function, eliminating inhibition of protein synthesis mediated by 4E-BP1 and eEF2.

Secretory carcinoma of the breast commonly occurs at a later age than previously recognized, and is associated with good long-term survival.

A subset of obese humans has relatively low plasma levels of leptin. This finding has suggested that in some cases abnormal regulation of the leptin gene in adipose tissue is etiologic in the pathogenesis of the obese state. The possibility that a relative decrease in leptin production can lead to obesity was tested by mating animals carrying a weakly expressed adipocyte specific aP2-human leptin transgene to C57BL͞6J ob͞ob mice (which do not express leptin). The transgene does not contain the regulatory elements of the leptin gene and is analogous to a circumstance in which the cis elements and͞or trans factors regulating leptin RNA production are abnormal. The ob͞ob mice carrying the transgene had a plasma leptin level of 1.78 ng͞ml, which is Ϸone-half that found in normal, nontransgenic mice (3.72 ng͞ml, P < 0.01). The ob͞ob animals expressing the leptin transgene were markedly obese though not as obese as ob͞ob mice without the transgene. The infertility as well as several of the endocrine abnormalities generally evident in ob͞ob mice were normalized in the ob͞ob transgenic mice. However, the ob͞ob transgenic mice had an abnormal response when placed at an ambient temperature of 4°C, suggesting that different thresholds exist for the different biologic effects of leptin. Leptin treatment of the ob͞ob transgenic mice resulted in marked weight loss with efficacy similar to that seen after treatment of wild-type mice. In aggregate these data suggest that dysregulation of leptin gene can result in obesity with relatively normal levels of leptin and that this form of obesity is responsive to leptin treatment.Many clinical studies have suggested the hypothesis that body weight is regulated by a ''set point mechanism'' (1-3). This hypothesis holds that individuals reach equilibrium at different weights. It is posited that when individuals are at their set point, compensatory mechanisms resist weight change in either direction. The observation that weight loss in both lean and obese subjects is associated with reduced energy expenditure supports the set point hypothesis as does the high recidivism rate among obese subjects who lose weight by dieting (4, 5).A possible molecular basis for differences in weight among individuals has been suggested with the cloning of the ob gene and the identification of leptin (6-12). In principle, differences in leptin sensitivity and͞or production of leptin could lead to differences in weight. It has been suggested that high plasma levels of leptin and͞or increased levels of leptin RNA in obese subjects is indicative of leptin resistance (13-17). Indeed, 90-95% of obese humans have high leptin levels as do all forms of rodent obesity that have been analyzed (with the exception of leptin-deficient ob͞ob mice). Treatment of several strains of obese rodents with leptin has confirmed that high leptin levels indicate complete or partial leptin resistance (18,19).A subset of obese humans have normal or relatively low leptin levels (Ϸ5-10% of subjects) (13,14). In these individuals...

No abstract

The leptin receptor (Ob-R) is alternatively spliced into at least five different RNAs designated Ob-R(a-e). Ob-R(a-d) predict receptors with a single transmembrane domain, and Ob-Re predicts a secreted form of the receptor. The presence of an ϳ120-kDa soluble leptin receptor in mouse plasma was confirmed by precipitation with leptin-Sepharose beads followed by immunobloting with anti-leptin receptor antibodies. The soluble leptin receptor is larger than that predicted by the primary sequence. Deglycosylation of the receptor with peptide N:glycosidase F results in a decrease in molecular mass to a size consistent with that of the primary sequence. Leptin is an adipocyte hormone that functions as an afferent signal in a negative feedback loop regulating body weight (1). Administration of exogenous leptin to rodents results in a dose-dependent loss of adipose tissue mass (2-7). Leptin exerts its weight-reducing effects via interaction with a receptor, Ob-R, which is localized in the hypothalamus and other tissues (8, 9). Ob-R is a member of the cytokine receptor family and is alternatively spliced. Four of the splice variants, Ob-R(a-d), encode a receptor with a single transmembrane domain and a cytoplasmic region of variable length (9). Ob-Rb encodes a leptin receptor with a long intracytoplasmic region that contains several motifs known to be important for protein-protein interactions and signal transduction (9, 10). One of the splice variants, Ob-Re, does not encode a transmembrane domain and predicts a secreted form of the receptor (11).The db gene has been shown to be allelic with Ob-R. Three mouse alleles of db are available, each of which leads to severe early onset obesity and diabetes. The C57BL/Ks db/db mutation affects splicing of Ob-R and leads to the specific loss of Ob-Rb RNA (9, 10). db 3J /db 3J mice carry a frameshift mutation in the amino terminus of the receptor that affects all of the splice forms (11). The nature of these mutations predicts that C57BL/Ks db/db mice should be missing only the Ob-Rb isoform and that 129 db 3J /db 3J mice should carry mutations of all receptor forms. As the basis for the db Pas /db Pas mutation was not previously known, the affect of this allele on receptor protein(s) could not be predicted.Assays of the plasma levels of Ob-R protein were made in wild type and mutant mice. Specific antibodies to Ob-R were used to assay for the presence of Ob-Re, the secreted form of the leptin receptor, in plasma from wild type and mutant mice. An ϳ120-kDa protein corresponding to a glycosylated form of Ob-Re circulates in plasma from wild type and C57BL/Ks db/db mice. / dbPas mice were shown to carry a duplication in the extracellular region of Ob-R that ablates expression of all of the receptor variants.

Obesity may negatively impact survival, with differences among tumor subtypes.

We describe the clinical course of a recurrent case of congenital fibrosarcoma diagnosed in a 9-mo-old boy with a history of hemimelia. Following complete surgical resection of the primary tumor, the patient subsequently presented with bulky bilateral pulmonary metastases 6 mo following surgery. Molecular characterization of the tumor revealed the absence of the prototypical ETV6-NTRK3 translocation. However, tumor characterization incorporating cytogenetic, array comparative genomic hybridization, and RNA sequencing analyses, revealed a somatic t(2;15)(2p21;15q25) translocation resulting in the novel fusion of EML4 with NTRK3. Cloning and expression of EML4-NTRK3 in murine fibroblast NIH 3T3 cells revealed a potent tumorigenic phenotype as assessed in vitro and in vivo. These results demonstrate that multiple fusion partners targeting NTRK3 can contribute to the development of congenital fibrosarcoma.

In cancer progression, carcinoma cells gain invasive behavior through a loss of epithelial characteristics and acquisition of mesenchymal properties, a process that can lead to epithelial-mesenchymal transition (EMT). TGF-b is a potent inducer of EMT, and increased TGF-b signaling in cancer cells is thought to drive cancer-associated EMT. Here, we examine the physiological requirement for mTOR complex 2 (mTORC2) in cells undergoing EMT. TGF-b rapidly induces mTORC2 kinase activity in cells undergoing EMT, and controls epithelial cell progression through EMT. By regulating EMT-associated cytoskeletal changes and gene expression, mTORC2 is required for cell migration and invasion. Furthermore, inactivation of mTORC2 prevents cancer cell dissemination in vivo. Our results suggest that the mTORC2 pathway is an essential downstream branch of TGF-b signaling, and represents a responsive target to inhibit EMT and prevent cancer cell invasion and metastasis.