Signaling pathways involved in regulation of glucose -6 -phosphate dehydrogenase (G6PD) by arachidonic acid

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of pentose phosphate pathway and provides NADPH for de novo fatty acid biosynthesis. For the later reason, G6PD is known as a lipogenic enzyme. Insulin induces expression of G6PD mRNA via activating the PI3 kinase pathway in primary rat hepatocytes. Addition of arachidonic acid, a polyunsaturated fatty acid, in the medium interferes with the PI3 kinase pathway, and thus inhibits the insulin-mediated induction of G6PD. Arachidonic acid in the presence of insulin induces p38 MAP kinase pathway over insulin treatment alone. Activation of p38 MAP kinase by arachidonic acid interferes with the insulin signal transduction pathway by phosphorylating IRS-1 at Ser-307 and preventing PI3 kinase activation and Akt-phosphorylation. Inhibition of the p38 MAP kinase pathway by using a specific inhibitor, SB203580, attenuates the inhibitory effect of arachidonic acid on G6PD and at the same time reverses its effect on IRS-1 and Akt-phosphorylation.;Arachidonic acid also activates AMP-activated protein kinase (AMPK) in primary rat hepatocytes by phosphorylating it at Thr-172. Activators of AMPK, AICAR and metformin inhibit the induction of G6PD mRNA by insulin. AICAR induces phosphorylation of p38 MAP kinase in primary rat hepatocytes. AICAR-mediated inhibition of G6PD mRNA expression is dependent on the activation of the p38 MAP kinase pathway, as in the presence of the p38 MAP kinase inhibitor the inhibitory effect of AICAR on G6PD mRNA expression is abolished. AICAR also interferes with PI3 kinase pathway by inducing Ser-307 phosphorylation of IRS-1 and inhibiting Akt phosphorylation. Thus, this AMPK activator mimics the effect of arachidonic acid both on insulin signaling pathway and on G6PD mRNA expression.;Activation of the mammalian target of rapamycin (mTOR) pathway by insulin is required for the insulin-mediated induction of G6PD mRNA expression. Arachidonic acid inhibits the phosphorylation of the downstream effector protein of mTOR, S6K-1 at Thr-389 which suggests it interferes with activation of mTOR. This provides an indirect evidence of the activation of AMPK by arachidonic acid in primary rat hepatocytes, as activation of AMPK results in the inhibition of mTOR/S6K-1 pathway. However, inhibition of mTOR, rather than activation, rules out the possibility of involvement of this pathway in the interference of the PI3 kinase activation upon arachidonic acid treatment. We also have ruled out the possibility of involvement of protein kinase C (PKC), as neither activators of PKC mimic the action of arachidonic acid on G6PD nor inhibitors of PKC can abolish the effect of arachidonic acid on G6PD mRNA expression

COUGH AND CHEST PAIN WITH AN UNCOMMON CAUSE

Multiple  Hereditary  Exostoses  is  an  autosomal  dominant  disorder  with  multiple  cartilage  capped  bony  outgrowths  in  tibia  ,fibula, femur,  and  sometimes  the  ribs  and  scapula. They may  present  with  variety  of  symptoms  depending  on  the  structures  it  compresses  such  as  nerves,  arteries  or  may  lead  to  limb  deformities  or  may  cause  bursitis , or  may  undergo  malignant  transformation. A  33 year old  male  presented  to  our  outpatient  department  with  recurrent  cough  and  left  sided  chest  pain. On  evaluation  he  was  found  to  have  multiple  bony  outgrowths  in the scapula ,5th  rib , and  limbs. Similar  bony  outgrowths  were  also  present  in  his  father  and  grandfather. On  clinical  and  radiological  basis  a  diagnosis of  Multiple  Hereditary  Exostoses  was  made. His  symptoms  gradually  subsided  with  removal  of  the  rib  and  scapular  exostoses. Thus  evaluation  of  bony  structures  should  not  be  overlooked  in  cases  of  cough  and  chest  pain.Keywords: Cough, Chestpain, Multiple  Hereditary  Exostoses.Â

hnRNP A1 and hnRNP F Modulate the Alternative Splicing of Exon 11 of the Insulin Receptor Gene

Exon 11 of the insulin receptor gene (INSR) is alternatively spliced in a developmentally and tissue-specific manner. Linker scanning mutations in a 5′ GA-rich enhancer in intron 10 identified AGGGA sequences that are important for enhancer function. Using RNA-affinity purification and mass spectrometry, we identified hnRNP F and hnRNP A1 binding to these AGGGA sites and also to similar motifs at the 3′ end of the intron. The hnRNPs have opposite functional effects with hnRNP F promoting and hnRNP A1 inhibiting exon 11 inclusion, and deletion of the GA-rich elements eliminates both effects. We also observed specific binding of hnRNP A1 to the 5′ splice site of intron 11. The SR protein SRSF1 (SF2/ASF) co-purified on the GA-rich enhancer and, interestingly, also competes with hnRNP A1 for binding to the splice site. A point mutation -3U→C decreases hnRNP A1 binding, increases SRSF1 binding and renders the exon constitutive. Lastly, our data point to a functional interaction between hnRNP F and SRSF1 as a mutant that eliminates SRSF1 binding to exon 11, or a SRSF1 knockdown, which prevents the stimulatory effect of hnRNP F over expression

Diabetogenic Microbiome - A Review on the Microbes Involve in Diabetes

Diabetes has emerged as a pandemic and has caused a great percentage of mortality all over the world according to the World Health Organization (WHO). This worldwide health issue has turned to be a major concern as it shares its role in the onset and progression of many other metabolic diseases along with it. Several factors that include microbes such as bacteria and viruses, diet, and lifestyle comes into play in the progression of this autoimmune disease. Studies done on humans and experimental animal models have provided a great deal of knowledge on how bacteria and viruses are involved in the pathogenesis of diabetes. Nevertheless, the need for more investigations is required to understand the relationship between the microbes and disease development. This review deals with the underlying reasons of diabetes Type I and Type II especially with respect to the microbes in the body and the subsequent changes caused through them

SRp20 and CUG-BP1 Modulate Insulin Receptor Exon 11 Alternative Splicing▿

The insulin receptor (IR) exists as two isoforms, IR-A and IR-B, which result from alternative splicing of exon 11 in the primary transcript. This alternative splicing is cell specific, and the relative proportions of exon 11 isoforms also vary during development, aging, and different disease states. We have previously demonstrated that both intron 10 and exon 11 contain regulatory sequences that affect IR splicing both positively and negatively. In this study, we sought to define the precise sequence elements within exon 11 that control exon recognition and cellular factors that recognize these elements. Using minigenes carrying linker-scanning mutations within exon 11, we detected both exonic splicing enhancer and exonic splicing silencer elements. We identified binding of SRp20 and SF2/ASF to the exonic enhancers and CUG-BP1 to the exonic silencer by RNA affinity chromatography. Overexpression and knockdown studies with hepatoma and embryonic kidney cells demonstrated that SRp20 and SF2/ASF increase exon inclusion but that CUG-BP1 causes exon skipping. We found that CUG-BP1 also binds to an additional intronic splicing silencer, located at the 3′ end of intron 10, to promote exon 11 skipping. Thus, we propose that SRp20, SF2/ASF, and CUG-BP1 act antagonistically to regulate IR alternative splicing in vivo and that the relative ratios of SRp20 and SF2/ASF to CUG-BP1 in different cells determine the degree of exon inclusion