No abstract

Granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates cellular glucose uptake by decreasing the apparent K m for substrate transport through facilitative glucose transporters on the plasma membrane. Little is known about this signal transduction pathway and the role of the ␣ subunit of the GM-CSF receptor (␣GMR) in modulating transporter activity. We examined the function of phosphatidylinositol 3-kinase (PI 3-kinase) in GM-CSF-stimulated glucose uptake and found that PI 3-kinase inhibitors, wortmannin and LY294002, completely blocked the GM-CSF-dependent increase of glucose uptake in Xenopus oocytes expressing the low affinity ␣GMR and in human cells expressing the high affinity ␣␤GMR complex. We identified a Src homology 3 domain-binding motif in ␣GMR at residues 358 -361 as a potential interaction site for the PI 3-kinase regulatory subunit, p85. Physical evidence for p85 binding to ␣GMR was obtained by co-immunoprecipitation with antibodies to ␣GMR and p85, and an ␣GMR mutant with alteration of the Src homology 3 binding domain lost the ability to bind p85. Experiments with a construct eliminating most of the intracellular portion of ␣GMR showed a 50% reduction in GM-CSF-stimulated glucose uptake with residual activity blocked by wortmannin. Searching for a proximally generated diffusible factor capable of activating PI 3-kinase, we identified hydrogen peroxide (H 2 O 2 ), generated by ligand or antibody binding to ␣GMR, as the initiating factor. Catalase treatment abrogated GM-CSF-or anti-␣GMR antibody-stimulated glucose uptake in ␣GMR-expressing oocytes, and H 2 O 2 activated PI 3-kinase and led to some stimulation of glucose uptake in uninjected oocytes. Human myeloid cell lines and primary explant human lymphocytes expressing high affinity GM-CSF receptors responded to ␣GMR antibody with increased glucose uptake. These results identify the early events in the stimulation of glucose uptake by GM-CSF as involving local H 2 O 2 generation and requiring PI 3-kinase activation. Our findings also provide a mechanistic explanation for signaling through the isolated ␣ subunit of the GM-CSF receptor.

Rationale-We investigated the molecular mechanism(s) that play a role in leptin signaling during the development of left ventricular hypertrophy (LVH) due to pressure overload. To this end, ob/ ob leptin deficient and C57BL/6J control mice were subjected transverse aortic constriction (TAC).Methods-Control sham C57BL/6J and ob/ob mice, along with C57BL/6J and ob/ob leptin deficient mice were subjected transverse aortic constriction (TAC) for 15 days and then evaluated for morphological, physiological, and molecular changes associated with pressure overload hypertrophy.Results-Evaluation by echocardiography revealed a significant increase in left ventricular mass (LVmass) and wall thickness in ob/ob mice subjected to transverse aortic constriction (TAC) as compared to C57BL/6J. Analysis of the expression of molecular markers of LVH, such as atrial natriuretic peptide (ANP), revealed a blunted increase in the level of ANP in ob/ob mice as compared to C57BL/6J mice. We observed that leptin plays a role in modulating the transcriptional activity of the promoter of the ANP gene. Leptin acts by regulating NFATc4, a member of the nuclear factor activated T cell (NFAT) family of transcription factors in cardiomyocytes. Our in vivo studies revealed that ob/ob mice subjected to TAC failed to activate the NFATc4 in the heart, however, intraperitoneal injection of leptin in ob/ob mice restored the NFATc4 DNA-binding activity and induced expression of the ANP gene.Conclusion-This study establishes the role of leptin as an anti-hypertrophic agent during pressure overload hypertrophy, and suggests that a key molecular event is the leptin mediated activation of NFATc4 that regulates the transcriptional activation of the ANP gene promoter.

Our results suggest that changes in the Hexim-1 protein expression and cellular distribution significantly influences the AR activation and the TGF-β signaling. Thus, Hexim-1 is likely to play a significant role in prostate cancer progression.