The effect of epidermal growth factor on the distribution of SGLT-1 in rabbit jejunum

The effect of epidermal growth factor (EGF) on the cellular and villous distribution of the sugar transporter SGLT-1 was examined. New Zealand White rabbits (1 kg) were anesthetized, and two jejunal blind loops were isolated and exposed to either 0.9% saline or EGF (60 ng/mL saline), for 1 h. In separate experiments, tissue was harvested for brush border membrane vesicles (BBMV), microsomal membranes, or fixed for immunohistochemistry. SGLT-1 was measured in membrane fractions by Western immunoblot or localized along the villus-crypt axis by immunofluorescent microscopy. EGF increased BBMV SGLT-1 content compared with paired controls. EGF stimulation also induced a corresponding decrease in microsomal SGLT-1 levels and induced the expression of additional SGLT-1 immunoreactivity further down the villus axis. The findings suggest that EGF upregulates intestinal glucose transport by stimulating the translocation of SGLT-1 from an internal microsomal pool into the brush border, thereby recruiting more villus enterocytes into the glucose transporting population.

Expression of glucose transporter-1 in cervical cancer and its precursors

OBJECTIVE

Increased glucose uptake and utilization is a known phenomenon exhibited by malignant cells. Overexpression of the glucose transporter protein family is thought to be the principal mechanism by which these cells achieve up-regulation. Our purpose is to determine glucose transporter-1 (GLUT 1) expression in squamous carcinoma of the cervix and precursor lesions.

METHODS

Archival histologic sections were obtained from 31 cases of invasive squamous cell carcinoma (SCC) of the uterine cervix, 15 cases of high-grade cervical intraepithelial neoplasia, 5 cases of low-grade, and 9 normal cervices. Immunohistochemistry for GLUT 1 protein was performed using polyclonal GLUT 1 antibody (Dako, Carpinteria, CA) and the labeled streptavidin-biotin procedure.

RESULTS

Compared to the internal control, the pattern of staining varied from weak (1+) to strong (3+) reactions. In normal cervix, 1+ GLUT 1 staining was seen in the basal cells of the squamous epithelium. All 31 (100%) cases of SCC were positive for GLUT 1. Positive reactions seemed more intense in tumor cells that were farther away from the stromal blood supply. There was a correlation between intensity of reaction for GLUT 1 and histologic grade of tumor (P = 0.0027) and with progression from normal or dysplastic lesions to invasive cancer (P = 0.0001). Intensity was a predictor of the presence of poorly differentiated tumor type. Low-grade CIN staining was seen in less than one-third of the epithelium, while in high-grade lesions the reaction was present in over one-half of the epithelium.

CONCLUSIONS

GLUT 1 is overexpressed in cervical carcinoma. The process appears to be related to grade of tumor but not to the progression from preneoplastic lesions. The results suggest that GLUT 1 overexpression is a late phenomenon in cellular transformation. Furthermore, the possible relation of expression to tumor blood supply suggests that the malignant cells may have an adaptive environmental ability to compensate for a compromised microenvironment.

Resistance training increases glucose uptake and transport in rat skeletal muscle

The aim of this investigation was to determine if resistance training exercise improved glucose uptake and transport in rodent skeletal muscle. Sprague-Dawley rats were assigned to one of the three groups: control (CON), resistance trained (RT) and aerobic exercise trained (AT). Resistance trained rats were placed in a rodent squat apparatus and performed three sets of 10 repetitions at 75% of their one repetition maximum 3 days week-1 for 12 weeks. Aerobic exercise training consisted of running the rats 3 days week-1 for 45 min over a 12-week period on a motor-driven treadmill (32 m min-1, 15% grade). Following the training period, all animals were subjected to hind limb perfusion in the presence of 500 microU mL-1 insulin. Hind limb glucose uptake was similar in the RT (9.91 +/- 0.7 micromol g-1 h-1) and AT (10.23 +/- 1.0 micromol g-1 h-1) animals and significantly greater than control (CON) (6.40 +/- 0.6 micromol g-1 h-1). Rates of 3-O-methyl-d-glucose transport in the RT animals were elevated in the muscles utilized for RT while in the AT animals rates of 3-O-methyl-d-glucose transport were increased in those muscles recruited for running. The increased rates of 3-O-methyl-d-glucose transport in the skeletal muscles of the resistance trained and aerobic exercise trained animals appeared to be, in part, because of an increased GLUT4 protein concentration. These findings suggest that both resistance or aerobic training exercise can improve insulin-stimulated skeletal muscle glucose uptake and transport, but the training adaptations are restricted to the muscles recruited for the exercise performance.

Expression of the GLUT1 glucose transporter in gallbladder carcinomas

BACKGROUND/AIMS

It has previously been shown that glucose uptake and use is more prevalent in carcinomas than in normal cells and tissues. We hypothesized that human erythrocyte glucose transporter-1 expression is increased in gallbladder carcinoma and might be correlated with prognostic significance.

METHODOLOGY

A total of 71 cases of gallbladder carcinomas, 2 cases of gallbladder dysplasia and 20 cases of gallbladder adenomas were examined immunohistochemically to evaluate the expression of glucose transporter-1 protein in the light of their relationship with various prognostic factors.

RESULTS

Glucose transporter-1 was stained in the cell membrane of the cancer cells. Adjacent normal mucosa was negative for glucose transporter-1 staining. Thirty-seven gallbladder carcinomas (52.1%) showed positive staining for glucose transporter-1, however only one of the adenomas (5.0%) and none of the dysplasias were positive (P < 0.05). There was significant correlation between glucose transporter-1 expression and histologic tumor type, and tumor stage. In the multivariate analysis, tumor stage was statistically significant (P = 0.05), but glucose transporter-1 expression was not significant (P = 0.07). The mean survival periods of the glucose transporter-1 positive and negative groups were 24 months and 58 months, respectively (P = 0.003).

CONCLUSIONS

Our results suggest that glucose transporter-1 protein expression is strongly associated with neoplastic progression in gallbladder carcinomas, and that glucose transporter-1 expression identifies with a worse prognosis in the patients with gallbladder carcinomas.

Nigericin inhibits insulin-stimulated glucose transport in 3T3-L1 adipocytes

We used nigericin, a K+/H+ exchanger, to test whether glucose transport in 3T3-L1 adipocytes was modulated by changes in intracellular pH. Our results showed that nigericin increased basal but decreased insulin-stimulated glucose uptake in a time- and dose-dependent manner. Whereas the basal translocation of GLUT1 was enhanced, insulin-stimulated GLUT4 translocation was inhibited by nigericin. On the other hand, the total amount of neither transporter protein was altered. The finding that insulin-stimulated phosphoinositide 3-kinase (PI 3-kinase) activity was not affected by nigericin implies that nigericin exerted its inhibition at a step downstream of PI 3-kinase activation. At maximal dose, nigericin rapidly lowered cytosolic pH to 6.7; however, this effect was transient and cytosolic pH was back to normal in 20 min. Removal of nigericin from the incubation medium after 20 min abolished its enhancing effect on basal but had little influence on its inhibition of insulin-stimulated glucose transport. Moreover, lowering cytosolic pH to 6.7 with an exogenously added HCl solution had no effect on glucose transport. Taken together, it appears that nigericin may inhibit insulin-stimulated glucose transport mainly by interfering with GLUT4 translocation, probably by a mechanism not related to changes in cytosolic pH.

Role of adenine nucleotides in insulin secretion from MIN6 pseudoislets

Insulin secretion from MIN6 cells configured as cell aggregates by culture on a gelatin substrate (pseudoislets) is enhanced compared to that of MIN6 cells grown as monolayers on tissue culture plastic, indicating the importance of beta-cell-to-beta-cell proximity for insulin release. In this study we have shown that glucose induced a biphasic release of insulin from pseudoislets, whereas the amplitude and duration of the responses of equivalent monolayer cells were much reduced. Purinergic aqonists have been implicated in intercellular communication between beta-cells, so we investigated whether adenine nucleotides co-released with insulin are responsible for the enhanced secretory responses of pseudoislets. We have demonstrated that MIN6 cells express purinergic A(1) and P2Y receptors, and that adenine nucleotides increased [Ca(2+)](i) with an efficacy of agonists being ATP > ADP > AMP. However, neither suramin nor the more selective A(1) antagonist 1,3-dipropyl-8-cyclopentylxanthine reduced glucose-induced insulin secretion from pseudoislets, and stimulation of monolayer cells with a range of adenine nucleotides did not enhance glucose-induced secretion. These results suggest that enhanced secretion from MIN6 pseudoislets is not due to increased paracrine/autocrine action of adenine nucleotides.

Immunolocalization of glucose transporter 1 and 3 in the placenta: application to cytodiagnosis of Papanicolaou smear

A positive immunostaining for glucose transporter 1 (GLUT1) was exclusively localized in microvilli on the free surface of syncytiotrophoblasts in the placenta. An enhanced immunoreaction for glucose transporter 3 (GLUT3) was elicited in the cell membrane of intermediate trophoblasts and cytotrophoblasts. Neither GLUT1 nor GLUT3 was positive in decidual cells and epithelial components from cervical dysplasia and carcinoma in situ. Cervicovaginal smears from six pregnant women containing atypical cells of unknown origin were subjected to immunocytochemical testing with antibodies against GLUT1 and GLUT3. Atypical cells in smears from two pregnant women were found to be positive for GLUT3 while no specific immunoreaction for GLUT1 was elicited, indicating their origin from either intermediate trophoblasts or cytotrophoblasts. Through the use of antibodies against vimentin and cytokeratin 17, GLUT3-negative atypical cells were further sorted into decidual cells and epithelial components from cervical dysplasia, respectively.

Role of PDK1 in insulin-signaling pathway for glucose metabolism in 3T3-L1 adipocytes

To investigate the role of 3-phosphoinositide-dependent protein kinase 1 (PDK1) in the insulin-signaling pathway for glucose metabolism, wild-type (wt), the kinase-dead (kd), or the plecstrin homology (PH) domain deletion (DeltaPH) mutant of PDK1 was expressed using an adenovirus gene transduction system in 3T3-L1 adipocytes. wt-PDK1 and kd-PDK1 were found in both membrane and cytosol fractions, whereas DeltaPH-PDK1, which exhibited PDK1 activity similar to that of wt-PDK1, was detected exclusively in the cytosol fraction. Insulin dose dependently activated protein kinase B (PKB) but did not change atypical protein kinase C (aPKC) activity in control cells. aPKC activity was not affected by expression of wt-, kd-, or DeltaPH-PDK1 in either the presence or the absence of insulin. Overexpression of wt-PDK1 enhanced insulin-induced activation of PKB as well as insulin-induced phosphorylation of glycogen synthase kinase (GSK)3alpha/beta, a direct downstream target of PKB, although insulin-induced glycogen synthesis was not significantly enhanced by wt-PDK1 expression. Neither DeltaPH-PDK1 nor kd-PDK1 expression affected PKB activity, GSK3 phosphorylation, or glycogen synthesis. Thus membrane localization of PDK1 via its PH domain is essential for insulin signaling through the PDK1-PKB-GSK3alpha/beta pathway. Glucose transport activity was unaffected by expression of wt-PDK1, kd-PDK1, or DeltaPH-PDK1 in either the presence or the absence of insulin. These findings suggest the presence of a signaling pathway for insulin-stimulated glucose transport in which PDK1 to PKB or aPKC is not involved.

Overexpression of c-Myc in beta-cells of transgenic mice causes proliferation and apoptosis, downregulation of insulin gene expression, and diabetes

To test the hypothesis that c-Myc plays an important role in beta-cell growth and differentiation, we generated transgenic mice overexpressing c-Myc in beta-cells under control of the rat insulin II promoter. F(1) transgenic mice from two founders developed neonatal diabetes (associated with reduced plasma insulin levels) and died of hyperglycemia 3 days after birth. In pancreata of transgenic mice, marked hyperplasia of cells with an altered phenotype and amorphous islet organization was displayed: islet volume was increased threefold versus wild-type littermates. Apoptotic nuclei were increased fourfold in transgenic versus wild-type mice, suggesting an increased turnover of beta-cells. Very few cells immunostained for insulin; pancreatic insulin mRNA and content were markedly reduced. GLUT2 mRNA was decreased, but other beta-cell-associated genes (IAPP [islet amyloid pancreatic polypeptide], PDX-1 [pancreatic and duodenal homeobox-1], and BETA2/NeuroD) were expressed at near-normal levels. Immunostaining for both GLUT2 and Nkx6.1 was mainly cytoplasmic. The defect in beta-cell phenotype in transgenic embryos (embryonic days 17-18) and neonates (days 1-2) was similar and, therefore, was not secondary to overt hyperglycemia. When pancreata were transplanted under the kidney capsules of athymic mice to analyze the long-term effects of c-Myc activation, beta-cell depletion was found, suggesting that, ultimately, apoptosis predominates over proliferation. In conclusion, these studies demonstrate that activation of c-Myc in beta-cells leads to 1) increased proliferation and apoptosis, 2) initial hyperplasia with amorphous islet organization, and 3) selective downregulation of insulin gene expression and the development of overt diabetes.

Phenotypic characteristics of the nucleus pulposus: expression of hypoxia inducing factor-1, glucose transporter-1 and MMP-2

Attempts to study the biology of the nucleus pulposus have been limited in scope due to the low rates of cell proliferation, difficulties in maintaining viable disc cells in culture and the absence of a clearly defined phenotype. The major objective of this communication is to construct a phenotypic signature for cells of the nucleus pulposus that is based on the hypothesis that in response to restriction on oxygen and nutrient flux, there is expression of HIF-1, GLUT-1 and MMP-2. Nucleus pulposus, as well as annulus fibrosus and cartilage of the vertebral end plates, was collected from rat spinal units. Western blot analysis and immunohistochemistry clearly showed that there was a significant level of expression of the HIF-1 beta isoform in the nucleus pulposus; HIF-1 beta was present at lower levels in cells of the annulus and the end plate. In contrast to HIF-1 beta, HIF-1 alpha was expressed only in the nucleus pulposus. This isoform was absent from both the cartilage end plate and annulus. We detected HIF-1 alpha immunohistochemically in the nucleus pulposus; however, the staining was light and diffuse. Cells of the nucleus pulposus expressed GLUT-1; in contrast, when probed by Western blot analysis the annulus and cartilage were negative for this protein. Western blot analysis also showed that in the nucleus pulposus the level of MMP-2 was high when compared to the adjacent tissues. We suggest that the differential expression of the two HIF isoforms, and GLUT-1 and MMP-2, provides a phenotypic signature that permits cells of the nucleus pulposus to be distinguished from neighboring tissues. Moreover, the presence of these isoforms provides evidence that cells of the disc respond to hypoxia and nutrient stress by upregulating stress-responsive genes.

The fatty acid translocase (FAT)/CD36 and the glucose transporter GLUT4 are localized in different cellular compartments in rat cardiac muscle

The fatty acid translocase (FAT)/CD36 plays an important role in the acute regulation of fatty acid uptake in muscle tissue. We studied the subcellular distribution of FAT/CD36 in rat cardiac muscle after in vivo insulin stimulation by membrane fractionation and immunoisolation of GLUT4- and FAT/CD36-vesicles. FAT/CD36 was equally present in both plasma and microsomal membranes with no effect of insulin on the cellular distribution, whereas GLUT4 increased 2- to 3-fold in the plasma membrane. FAT/CD36 resides in one intracellular pool, whereas GLUT4 is present in two distinct pools. Immunoadsorption of GLUT4-vesicles indicated that FAT/CD36 is undetectable in these vesicles. Likewise, no GLUT4 could be detected in FAT/CD36-vesicles. These vesicles contain a high amount of Rab11 that remained unaffected after insulin stimulation, whereas Rab11 increased about 3-fold in the GLUT4-vesicles in response to insulin. These data show that GLUT4 and FAT/CD36 do not co-localize in cardiac muscle and that FAT/CD36 is not redistributed in response to insulin in the heart. Rab11 may be involved in endosomal recycling of FAT/CD36, however, insulin-associated Rab11 functions appear to be limited to GLUT4-vesicles.

Intracellular insulin-responsive glucose transporter (GLUT4) distribution but not insulin-stimulated GLUT4 exocytosis and recycling are microtubule dependent

To investigate the potential role of microtubules in the regulation of insulin-responsive glucose transporter (GLUT4) trafficking in adipocytes, we examined the effects of microtubule depolymerizing and stabilizing agents. In contrast to previous reports, disruption or stabilization of microtubule structures had no significant effect on insulin-stimulated GLUT4 translocation. However, consistent with a more recent study (Molero, J. C., J. P. Whitehead, T. Meerloo, and D. E. James, 2001, J Biol Chem 276:43829-43835) nocodazole did inhibit glucose uptake through a direct interaction with the transporter itself independent of the translocation process. In addition, the initial rate of GLUT4 endocytosis was not significantly affected by microtubule depolymerization. However, these internalized GLUT4 compartments are confined to regions just beneath the plasma membrane and were not exposed to the extracellular space. Furthermore, they were unable to undergo further sorting steps and trafficking to the perinuclear region. Nevertheless, these apparent early endocytic GLUT4 compartments fully responded to a second insulin stimulation with an identical extent of plasma membrane translocation. Together, these data demonstrate that although microtubular organization may play a role in the trafficking of GLUT4 early endocytic vesicles back to the perinuclear region, they do not have a significant role in insulin-stimulated GLUT4 exocytosis, initial endocytosis from the plasma membrane and/or recycling back to the plasma membrane.

Acyl-coenzyme A dehydrogenases are localized on GLUT4-containing vesicles via association with insulin-regulated aminopeptidase in a manner dependent on its dileucine motif

Insulin-regulated aminopeptidase (IRAP, also termed vp165) is known to be localized on the GLUT4-containing vesicles and to be recruited to the plasma membrane after stimulation with insulin. The cytoplasmic region of IRAP contains two dileucine motifs and acidic regions, one of which (amino acid residues 55-82) is reportedly involved in retention of GLUT4-containing vesicles. The region of IRAP fused with glutathione-S-transferase [GST-IRAP(55-82)] was incubated with lysates from 3T3-L1 adipocytes, leading to identification of long-chain, medium-chain, and short-chain acyl-coenzyme A dehydrogenases (ACDs) as the proteins associated with IRAP. The association was nearly abolished by mutation of the dileucine motif of IRAP. Immunoblotting of fractions prepared from sucrose gradient ultracentrifugation and vesicles immunopurified with anti-GLUT4 antibody revealed these ACDs to be localized on GLUT4-containing vesicles. Furthermore, 3-mercaptopropionic acid and hexanoyl-CoA, inhibitors of long-chain and medium-chain ACDs, respectively, induced dissociation of long-chain acyl-coenzyme A dehydrogenase and/or medium-chain acyl-coenzyme A dehydrogenase from IRAP in vitro as well as recruitment of GLUT4 to the plasma membrane and stimulation of glucose transport activity in permeabilized 3T3-L1 adipocytes. These findings suggest that ACDs are localized on GLUT4-containing vesicles via association with IRAP in a manner dependent on its dileucine motif and play a role in retention of GLUT4-containing vesicles to an intracellular compartment.

Regional differences in transport, lipid composition, and fluidity of apical membranes of small intestine of chicken

Na+-dependent D-glucose transport was studied in brush-border membrane vesicles from duodenum, jejunum, and ileum of 5- to 6-wk-old chickens. Regional differences were found, and both initial rates and accumulation ratio of D-glucose were higher in the proximal part of the small intestine than in the ileum. To establish the mechanism(s) underlying these differences we have studied the density of Na+-dependent D-glucose cotransporter (SGLT1) as well as lipid composition and fluidity. Phlorizin-specific binding and Western blot analysis indicated a decrease in the amount of SGLT1 in the ileum when compared to the duodenum and jejunum. The distal part of the small intestine also showed a decrease in free cholesterol content and saturated-to-unsaturated fatty acid ratio together with an increase in lipid content and phosphatidylcholine-to-sphingomyelin ratio. These results were associated with a decrease in the diphenylhextriene fluorescence polarization found in brush-border membranes of the ileum. We can conclude that the decrease in the apical D-glucose transport found in the ileum is primarily due to a reduction in the amount of SGLT1 present in the brush-border membrane rather than the differences in the lipid composition and fluidity.

Isolation and characterization of the two major intracellular Glut4 storage compartments

In rat adipose cells, intracellular Glut4 resides in two distinct vesicular populations one of which contains cellugyrin whereas another lacks this protein (Kupriyanova, T. A., and Kandror, K. V. (2000) J. Biol. Chem. 275, 36263--36268). Cell surface biotinylated MPR and (125)I-labeled transferrin are accumulated in cellugyrin-positive vesicles and to a lesser extent in cellugyrin-negative vesicles. An average cellugyrin-positive vesicle carries not more than one molecule of either Glut4, insulin-responsive aminopeptidase (IRAP), or transferrin receptor (TfR), whereas cellugyrin-negative vesicles contain five to six molecules of Glut4, more than 10 molecules of IRAP, and still one molecule of TfR per vesicle. Cellugyrin-negative vesicles are translocated to the cell surface after insulin stimulation, whereas cellugyrin-positive vesicles maintain intracellular localization both in the absence and in the presence of insulin and, therefore, may be involved in interendosomal protein transport. Both cellugyrin-positive and cellugyrin-negative vesicles are present in extracts of non-homogenized cells and therefore may represent the major form of Glut4 storage in vivo.

Ontogenetic expression and regulation of Na(+)-D-glucose cotransporter in jejunum of domestic chicken

To evaluate the effect of age on sugar transport, we determined the uptake of methyl alpha-D-glucopyranoside and the abundance of the Na(+)-D-glucose cotransporter (SGLT1) in jejunal brush-border membrane (BBM) vesicles of 2-day- and 5-wk-old chickens. Methyl alpha-D-glucopyranoside transport per BBM protein was 40% lower in adults than in newly hatched chickens. This finding was matched by parallel declines in site density of SGLT1, which were detected by Western blot. The immunohistochemical study showed that SGLT1 was exclusively located in the BBM of enterocytes along the entire villus and was absent in the crypt in both age groups, and there was an 11-fold increase in the total absorptive area during development. Northern blot studies of the abundance of SGLT1 mRNA showed similar levels for the groups studied. We conclude that the age-related decline in Na(+)-dependent hexose transport per unit of BBM protein in the chicken jejunum is due to a reduction in the density of SGLT1 cotransporter and is regulated by a posttranscriptional mechanism.

Oxyphil parathyroid carcinomas: a clinicopathologic and immunohistochemical study of 10 cases

Oxyphil parathyroid carcinomas are uncommon neoplasms, and the clinicopathologic features of these tumors are largely unknown. We evaluated the clinicopathologic features of oxyphil parathyroid carcinomas and the expression of cytokeratin 14 (CK14), the high-affinity glucose transporter-4 (Glut-4), as well as the cell cycle proteins p27 and Ki67 and compared these with oxyphil parathyroid adenomas and chief cell parathyroid adenomas and carcinomas. Formalin-fixed, paraffin-embedded archival tissues from primary (n = 6) and recurrent (n = 4) oxyphil carcinomas were analyzed and compared with chief cell parathyroid carcinomas (n = 12), oxyphil parathyroid adenomas (n = 38), and chief cell parathyroid adenomas (n = 17) by immunohistochemistry for CK14, Glut-4, p27, and Ki67 using the avidin-biotin peroxidase system. Patients with primary oxyphil and chief cell carcinoma presented with high levels of serum calcium (n = 15.5 and 13.7 mg/dL, respectively). Approximately half the patients in each group died of disease. The Ki67 labeling index was higher (4.9 vs 1.9) and the p27 index lower (23 vs 66) in primary oxyphil carcinoma compared with primary oxyphil adenomas. CK14 was expressed in most oxyphil adenomas (35 of 38 cases) but not in oxyphil carcinomas (0 of 10 cases). Glut-4 was more commonly expressed in both groups of adenomas compared with carcinomas. These results show that oxyphil parathyroid carcinomas are functional malignancies similar to chief cell carcinomas and are associated with hypercalcemia, recurrence, and death. Expression of CK14 is very different in oxyphil adenomas compared with carcinomas. Although distinction between parathyroid adenomas and carcinomas can only be made by histopathologic and clinical findings, these results suggest that immunostaining for CK14, p27, and Ki67 may provide additional information to help distinguish between difficult cases of parathyroid adenomas and carcinomas. These findings also indicate that the same histopathologic features should be used to diagnose oxyphil and chief cell parathyroid carcinomas.

Identification of a novel glucose transporter-like protein-GLUT-12

Facilitative glucose transporters exhibit variable hexose affinity and tissue-specific expression. These characteristics contribute to specialized metabolic properties of cells. Here we describe the characterization of a novel glucose transporter-like molecule, GLUT-12. GLUT-12 was identified in MCF-7 breast cancer cells by homology to the insulin-regulatable glucose transporter GLUT-4. The GLUT-12 cDNA encodes 617 amino acids, which possess features essential for sugar transport. Di-leucine motifs are present in NH(2) and COOH termini at positions similar to the GLUT-4 FQQI and LL targeting motifs. GLUT-12 exhibits 29% amino acid identity with GLUT-4 and 40% to the recently described GLUT-10. Like GLUT-10, a large extracellular domain is predicted between transmembrane domains 9 and 10. Genomic organization of GLUT-12 is highly conserved with GLUT-10 but distinct from GLUTs 1-5. Immunofluorescence showed that, in the absence of insulin, GLUT-12 is localized to the perinuclear region in MCF-7 cells. Immunoblotting demonstrated GLUT-12 expression in skeletal muscle, adipose tissue, and small intestine. Thus GLUT-12 is potentially part of a second insulin-responsive glucose transport system.

Diagnostic utility of Glut-1 and CA 15-3 in discriminating adenocarcinoma from hepatocellular carcinoma in liver tumors biopsied by fine-needle aspiration

BACKGROUND

Diagnosing liver tumors can be difficult in the setting of a poorly differentiated tumor or tumors with no known prior malignancy. Frequently, alpha-fetoprotein, carcinoembryonic antigen, factor VIII, and mucicarmine have been employed to distinguish hepatocellular carcinoma (HCC) from adenocarcinoma. However, these stains have their limitations. CA 15-3 and Glut-1 are expressed in a variety of carcinomas. To the authors' knowledge, their expression in HCC has not been studied extensively. The authors examined the clinical utility of CA 15-3 and Glut-1 in the setting of fine-needle aspiration biopsy samples from the liver.

METHODS

Thirty-five cases of HCC and 59 cases of tumors metastatic to the liver were studied. These cases previously were studied with the hepatocyte paraffin-1 antibody. Each case was stained with CA 15-3 and Glut-1 using the avidin-biotin complex method. Each case was evaluated in a blinded fashion for membranous staining that was stronger than cytoplasmic or background staining. The diagnoses were unblinded and staining patterns were compared.

RESULTS

CA 15-3 stained 43 of 59 metastatic carcinoma samples and 3 of 35 HCC samples. Glut-1 stained 34 of 59 metastases and 2 of 35 HCCs. Together, the 2 immunostains stained 51 of 59 metastases and 5 of 35 HCCs. Diagnostic accuracy was improved by adding hepatocyte paraffin-1 to the staining panel.

CONCLUSIONS

CA 15-3 and Glut-1, especially in conjunction with hepatocyte paraffin-1, appear to be helpful in discriminating HCC from other carcinomas.

Vimentin affects localization and activity of sodium-glucose cotransporter SGLT1 in membrane rafts

It has been reported that vimentin, a cytoskeleton filament that is expressed only in mesenchymal cells after birth, is re-expressed in epithelial cells in vivo under pathological conditions and in vitro in primary culture. Whether vimentin re-expression is only a marker of cellular dedifferentiation or is instrumental in the maintenance of cell structure and/or function is a matter of debate. To address this issue, we used renal proximal tubular cells in primary culture from vimentin-null mice (Vim-/-) and from wild-type littermates (Vim+/+). The absence of vimentin did not affect cell morphology, proliferation and activity of hydrolases, but dramatically decreased Na-glucose cotransport activity. This phenotype was associated with a specific reduction of SGLT1 protein in the detergent-resistant membrane microdomains (DRM). In Vim+/+cells, disruption of these microdomains by methyl-β-cyclodextrin decreased SGLT1 protein abundance in DRM, a change that was paralleled by a decrease of Na-glucose transport activity. Importantly, we showed that vimentin is located to DRM, but it disappeared after methyl-β-cyclodextrin treatment. In Vim-/- cells,supplementation of cholesterol with cholesterol-methyl-β-cyclodextrin complexes completely restored Na-glucose transport activity. Interestingly,neither cholesterol content nor cholesterol metabolism changed in Vim-/- cells. Our results are consistent with the view that re-expression of vimentin in epithelial cells could be instrumental to maintain the physical state of rafts and, thus, the function of DRM-associated proteins.

Glut3 expression in biopsy specimens of laryngeal carcinoma is associated with poor survival

OBJECTIVES/HYPOTHESIS

The aim of the study was to determine the clinical significance of the expression of Glut1 and Glut3 proteins in biopsy specimens of squamous cell carcinoma (SCC) of the larynx.

STUDY DESIGN

A retrospective study.

METHODS

Using immunohistochemistry, we immunostained sections of formalin-fixed, paraffin-embedded tissues from 48 biopsies of invasive SCC of the larynx for Glut1 and Glut3. The percentages of positive cells were recorded, then correlated with overall patient survival using the Kaplan-Meier method and the Breslow-Gehan-Wilcoxon test for statistical significance.

RESULTS

All cases were positive for Glut1, and Glut1 expression was not associated with survival difference at any cut-off value. Eighteen (38%) of the cases were Glut3-negative and 30 (62%) were Glut3-positive. Glut3-positive cases were associated with poorer survival than Glut3-negative cases (P =.0336). No significant difference was found between Glut3-negative and Glut3-positive groups in respect to sex, tumor site (glottic vs. supraglottic), nodal or distant metastasis, or treatment modality. However, there were significantly more poorly differentiated tumors in the Glut3-positive group than in the Glut3-negative group (27% vs. 0%, respectively; P =.0182, Fisher's Exact Test). After poorly differentiated tumors were excluded from the survival analysis, Glut3 immunoreactivity remained a significant marker of poor prognosis (P =.0385).

CONCLUSION

Immunohistochemical detection of Glut3 in biopsy specimens of SCC of the larynx is a marker of poorer prognosis.

Altered beta-cell distribution of pdx-1 and GLUT-2 after a short-term challenge with a high-fat diet in C57BL/6J mice

Mechanisms involved in the islet adaptation to insulin resistance were examined in mice of the C57BL/6J strain challenged with a high-fat (58%) diet for 8 weeks. Basal hyperglycemia commenced after 1 week, whereas hyperinsulinemia evolved after 8 weeks. Glucose elimination after an intravenous glucose challenge (1 g/kg) was significantly delayed after 1, 4, and 8 weeks on the high-fat diet compared with normal-diet-fed mice. This result was associated with unchanged insulin responses. However, glucose-stimulated insulin secretion from isolated islets was increased in a compensatory fashion at all glucose levels over a wide range (3.3-22 mmol/l) after 8 weeks on the high-fat diet, whereas no compensatory hypersecretion of insulin was evident after 1 or 4 weeks, except at 22 mmol/l glucose. Immunohistochemistry revealed that the islet architecture of insulin and glucagon cells remained intact in islets from mice fed a high-fat diet. However, the nuclear translocation of the homeobox transcription factor, pdx-1, and the plasma membrane translocation of GLUT2 were both impaired in high-fat-fed animals after 1 week. In contrast, the expression of the full-length leptin receptor (ObRb) was not affected by high-fat feeding. The study thus shows that 8 weeks are required for the development of a compensatory hypersecretion of insulin after high-fat feeding in mice, and even then the in vivo insulin secretion is insufficient to normalize impaired glucose tolerance. The early-onset islet dysfunction is accompanied by impaired beta-cell trafficking of two factors, pdx-1 and GLUT-2, which are involved in beta-cell proliferation and glucose recognition. The mechanisms compromising this beta-cell trafficking remain to be established.

A protective role for HIF-1 in response to redox manipulation and glucose deprivation: implications for tumorigenesis

We have investigated the role of HIF-1 in the cellular response to redox modulation via the inhibition of oxidative phosphorylation. We demonstrate that manipulation of redox in air, achieved by inhibiting cytochrome oxidase with cyanide, induces HIF-1 mediated transcription in wild-type CHO and HT1080 human tumour cells but not in CHO cells deficient in the oxygen responsive, HIF-1alpha sub-unit of HIF-1. Hypoglycaemia attenuates cyanide-mediated transcription in non-transformed HIF-1 wild-type CHO cells but not the human tumour derived cell line. Cells lacking either HIF-1alpha, or the second composite sub-unit of HIF-1, HIF-1beta, were markedly more sensitive to the combined stress of perturbed redox and hypoglycaemia than wild-type cells. As such conditions together with hypoxia are prevalent in tumours, these data suggest that HIF-1 may have a protective role in adaptation to the tumour micro-environment. In support of this we demonstrate that HIF-1alpha deficient cells are less tumorigenic than wild-type cells. They showed a reduced growth rate when grown as xenografts in nude mice. This was not related to vascular parameters that were identical to those found in HIF-1 wild-type tumours. The HIF-1 deficient tumours lacked focal expression of Glut-1 in hypoxic tumour regions. Compromised glucose uptake and metabolic adaptation to the tumour micro-environment may form the basis of the reduced tumorigenicity associated with these cells.

Insulin treatment improves islet function in type 2 diabetic Chinese hamsters

To study whether normalization of hyperglycemia improves islet function in long-standing type 2 diabetes, hyperglycemic CHIG/Han subline of the genetic type 2 diabetic Chinese hamster (>15 mmol/l: n=23) were either treated with insulin implants (liberating 1 U/day) or vehicle for two weeks. Islets were isolated and incubated for 3 h in the presence of 10 mmol/l glucose with or without 0.1 mmol/l 3-isobutyl-1-methylxanthine (IBMX). Specimens were also taken for immunocytochemical analysis of insulin cells. Glucose-stimulated insulin secretion was reduced by 83% in the vehicle-treated diabetic hamsters compared to non-diabetic controls (p<0.001). This impairment was not improved by the two-week insulin treatment. IBMX potentiated glucose-stimulated insulin secretion; this effect was markedly reduced in vehicle-treated diabetics compared to controls (p<0.001). In fact, the linear relation between IBMX-potentiated and glucose-stimulated insulin secretion in controls was absent in islets from diabetic animals. The two week insulin treatment normalized this relation, although still the total insulin secretory response to IBMX and glucose was lower than in controls. Furthermore, the islet insulin content was significantly increased by the 2 week normalization of glucose and, finally, the severe degranulation and lowering of insulin staining in islet beta cells in diabetic animals were markedly improved by insulin treatment. The results suggest that two-weeks of normalization of glycemia in long-standing type 2 diabetes in non-obese Chinese hamster improves beta cell signaling induced by the cyclic AMP pathway in conjunction with improved islet insulin content and beta cell morphology.

Effect of epidermal growth factor on intestinal adaptation after allogeneic small bowel transplantation in rats

We reported that epidermal growth factor (EGF) stimulated graft adaptation in a rat model of syngeneic small bowel transplantation. However, graft rejection is a severe problem with clinical small bowel transplantation, because small intestinal wall contains large amounts of lymphoid tissue. Studies were performed to investigate the effect of EGF on allogeneic graft adaptation after small bowel transplantation in rats treated with an immunosuppressant FK506. The transplanted animals received intraperitoneally EGF or saline (untreated) after surgery and were examined for analysis one week later. EGF-treated group markedly enhanced the water absorption and induction of sodium glucose cotransporter (SGLTI) as compared with EGF-untreated group. EGF-treated group also increased the mucosal crypt depth and its cell proliferating rate, although there was no significant difference in the mucosal villus height between the two groups. These results indicate that EGF accelerates intestinal allograft adaptation in part by the recovery of mucosal structure and function after small bowel transplantation in rats. EGF may have relevance to promote graft function in clinical small intestinal transplantation.