Distinct localization of GLUT-1, -3, and -5 in human monocyte-derived macrophages: effects of cell activation.

We determined subcellular localization of GLUT-1, GLUT-3, and GLUT-5 as human monocytes differentiate into macrophages in culture, and effects of the activating agents N-formyl-methionyl-leucyl-phenylalanine (fMLP) and phorbol myristate acetate (PMA). Western blot analysis demonstrated progressively increased GLUT-1, rapidly decreased GLUT-3, and a delayed increase of GLUT-5 expression during differentiation. Confocal microscopy revealed that each isoform displayed a unique subcellular distribution and cell-activation response. GLUT-1 was localized primarily to the cell surface but was also detected in the perinuclear region in a pattern characteristic of recycling endosomes. GLUT-3 exhibited predominantly a distinct vesicle-like staining but was present only in monocytes. GLUT-5 was found primarily at the cell surface but was detectable intracellularly. Activation with fMLP induced similar GLUT-1 and GLUT-5 redistributions from intracellular compartments toward the cell surface. PMA elicited a similar translocation of GLUT-1, but GLUT-5 was redistributed from the plasma membrane to a distinct intracellular compartment that appeared connected to the cell surface. These results suggest specific subcellular targeting of each transporter isoform and differential regulation of their trafficking pathways in cultured macrophages.

The midcycle increase in ovarian glucose uptake is associated with enhanced expression of glucose transporter 3. Possible role for interleukin-1, a putative intermediary in the ovulatory process.

This study characterizes the rat ovary as a site of hormonally dependent glucose transporter (Glut) expression, and explores the potential role of interleukin (IL)-1, a putative intermediary in the ovulatory process, in this regard. Molecular probing throughout a simulated estrous cycle revealed a significant surge in ovarian Glut3 (but not Glut1) expression at the time of ovulation. Treatment of cultured whole ovarian dispersates from immature rats with IL-1beta resulted in upregulation of the relative abundance of the Glut1 (4.5-fold) and Glut3 (3.5-fold) proteins as determined by Western blot analysis. Other members of the Glut family (i.e., Gluts 2, 4, and 5) remained undetectable. The ability of IL-1 to upregulate Glut1 and Glut3 transcripts proved time-, dose-, nitric oxide-, and protein biosynthesis-dependent but glucose independent. Other ovarian agonists (i.e., TNF alpha, IGF-I, interferon-gamma, and insulin) were without effect. Taken together, our findings establish the mammalian ovary as a site of cyclically determined Glut1 and Glut3 expression, and disclose the ability of IL-1 to induce the ovarian expression as well as translation of Glut1 and Glut3 (but not of Gluts 2, 4, or 5). Our observations also establish IL-1 as the first known regulator of Glut3, the most efficient Glut known to date. In so doing, IL-1, a putative component of the ovulatory process, may be acting to meet the increased metabolic demands imposed on the growing follicle and the ovulated cumulus-enclosed oocyte.

Expression of two glucose transporters, GLUT1 and GLUT3, in cultured cerebellar neurons: Evidence for neuron-specific expression of GLUT3.

The brain is dependent on glucose as an energy source and thus requires the expression of glucose transporter proteins to enable passage of glucose across both the endothelial cells of the blood-brain barrier and the plasma membranes of neurons and glia. The GLUT 1 isoform of the facilitative glucose transporter family is expressed in the blood-brain barrier; however, the major glucose transporter isoform(s) in neurons and glia have not been identified. We have investigated the expression of glucose transporters in cultured rat cerebellar granule neurons. Two isoforms, GLUT1 and GLUT3, were detected by Western and Northern blot analyses. Expression of both isoforms increased as neurons differentiated in culture, corresponding to an increase in glucose uptake. Localization of glucose transporters by immunofluorescence indicated the presence of both isoforms in neuronal processes and in the cell body. GLUT1 was detected in both plasma membrane and cytoplasm, whereas GLUT3 appeared only in plasma membrane. Significant GLUT3 expression was also detected in the neuronal cell lines PC12 and NG108 but not in primary cultured glia or C6 glioma cells. Our findings indicate that, in the rat brain, GLUT3 expression is predominantly in neurons, suggesting that this isoform may play a major role in neuronal glucose transport.