Inhibition of the PI 3-kinase pathway disrupts the unfolded protein response and reduces sensitivity to ER stress-dependent apoptosis.

Class Ia phosphoinositide 3-kinases (PI3K) are critical mediators of insulin and growth factor action. We have demonstrated that the p85α regulatory subunit of PI3K modulates the unfolded protein response (UPR) by interacting with and regulating the nuclear translocation of XBP-1s, a transcription factor essential for the UPR. We now show that PI3K activity is required for full activation of the UPR. Pharmacological inhibition of PI3K in cells blunts the ER stress-dependent phosphorylation of IRE1α and PERK, decreases induction of ATF4, CHOP, and XBP-1 and upregulates UPR target genes. Cells expressing a human p85α mutant (R649W) previously shown to inhibit PI3K, exhibit decreased activation of IRE1α and PERK and reduced induction of CHOP and ATF4. Pharmacological inhibition of PI3K, overexpression of a mutant of p85α that lacks the ability to interact with the p110α catalytic subunit (∆p85α) or expression of mutant p85α (R649W) in vivo, decreased UPR-dependent induction of ER stress response genes. Acute tunicamycin treatment of R649W+/- mice revealed reduced induction of UPR target genes in adipose tissue, whereas chronic tunicamycin exposure caused sustained increases in UPR target genes in adipose tissue. Finally, R649W+/- cells exhibited a dramatic resistance to ER stress-dependent apoptosis. These data suggest that PI3K pathway dysfunction causes ER stress that may drive the pathogenesis of several diseases including Type 2 diabetes and various cancers.

The E3 SUMO ligase PIASγ is a novel interaction partner regulating the activity of diabetes associated hepatocyte nuclear factor-1α.

The transcription factor hepatocyte nuclear factor-1α (HNF-1A) is involved in normal pancreas development and function. Rare variants in the HNF1A gene can cause monogenic diabetes, while common variants confer type 2 diabetes risk. The precise mechanisms for regulation of HNF-1A, including the role and function of post-translational modifications, are still largely unknown. Here, we present the first evidence for HNF-1A being a substrate of SUMOylation in cellulo and identify two lysine (K) residues (K205 and K273) as SUMOylation sites. Overexpression of protein inhibitor of activated STAT (PIASγ) represses the transcriptional activity of HNF-1A and is dependent on simultaneous HNF-1A SUMOylation at K205 and K273. Moreover, PIASγ is a novel HNF-1A interaction partner whose expression leads to translocation of HNF-1A to the nuclear periphery. Thus, our findings support that the E3 SUMO ligase PIASγ regulates HNF-1A SUMOylation with functional implications, representing new targets for drug development and precision medicine in diabetes.

Mice Carrying a Dominant-Negative Human PI3K Mutation Are Protected From Obesity and Hepatic Steatosis but Not Diabetes.

Phosphatidylinositol 3-kinase (PI3K) plays a central role in insulin signaling, glucose metabolism, cell growth, cell development, and apoptosis. A heterozygous missense mutation (R649W) in the p85α regulatory subunit gene of PI3K (PIK3R1) has been identified in patients with SHORT (Short stature, Hyperextensibility/Hernia, Ocular depression, Rieger anomaly, and Teething delay) syndrome, a disorder characterized by postnatal growth retardation, insulin resistance, and partial lipodystrophy. Knock-in mice with the same heterozygous mutation mirror the human phenotype. In this study, we show that Pik3r1 R649W knock-in mice fed a high-fat diet (HFD) have reduced weight gain and adipose accumulation. This is accompanied by reduced expression of several genes involved in lipid metabolism. Interestingly, despite the lower level of adiposity, the HFD knock-in mice are more hyperglycemic and more insulin-resistant than HFD-fed control mice. Likewise, when crossed with genetically obese ob/ob mice, the ob/ob mice carrying the heterozygous R649W mutation were protected from obesity and hepatic steatosis but developed a severe diabetic state. Together, our data demonstrate a central role of PI3K in development of obesity and fatty liver disease, separating these effects from the role of PI3K in insulin resistance and the resultant hyperglycemia.

Iris Malformation and Anterior Segment Dysgenesis in Mice and Humans With a Mutation in PI 3-Kinase.

Purpose: To determine the ocular consequences of a dominant-negative mutation in the p85α subunit of phosphatidylinositol 3-kinase (PIK3R1) using a knock-in mouse model of SHORT syndrome, a syndrome associated with short stature, lipodystrophy, diabetes, and Rieger anomaly in humans. Methods: We investigated knock-in mice heterozygous for the SHORT syndrome mutation changing arginine 649 to tryptophan in p85α (PIK3R1) using physical examination, optical coherence tomography (OCT), tonometry, and histopathologic sections from paraffin-embedded eyes, and compared the findings to similar investigations in two human subjects with SHORT syndrome heterozygous for the same mutation. Results: While overall eye development was normal with clear cornea and lens, normal anterior chamber volume, normal intraocular pressure, and no changes in the retinal structure, OCT images of the knock-in mouse eyes revealed a significant decrease in thickness and width of the iris resulting in increased pupil area and irregularity of shape. Both human subjects had Rieger anomaly with similar defects including thin irides and irregular pupils, as well as a prominent ring of Schwalbe, goniosynechiae, early cataract formation, and glaucoma. Although the two subjects had had diabetes for more than 30 years, there were no signs of diabetic retinopathy. Conclusions: A dominant-negative mutation in the p85α regulatory subunit of PI3K affects development of the iris, and contributes to changes consistent with anterior segment dysgenesis in both humans and mice.

Lipodystrophy Due to Adipose Tissue-Specific Insulin Receptor Knockout Results in Progressive NAFLD.

Ectopic lipid accumulation in the liver is an almost universal feature of human and rodent models of generalized lipodystrophy and is also a common feature of type 2 diabetes, obesity, and metabolic syndrome. Here we explore the progression of fatty liver disease using a mouse model of lipodystrophy created by a fat-specific knockout of the insulin receptor (F-IRKO) or both IR and insulin-like growth factor 1 receptor (F-IR/IGFRKO). These mice develop severe lipodystrophy, diabetes, hyperlipidemia, and fatty liver disease within the first weeks of life. By 12 weeks of age, liver demonstrated increased reactive oxygen species, lipid peroxidation, histological evidence of balloon degeneration, and elevated serum alanine aminotransferase and aspartate aminotransferase levels. In these lipodystrophic mice, stored liver lipids can be used for energy production, as indicated by a marked decrease in liver weight with fasting and increased liver fibroblast growth factor 21 expression and intact ketogenesis. By 52 weeks of age, liver accounted for 25% of body weight and showed continued balloon degeneration in addition to inflammation, fibrosis, and highly dysplastic liver nodules. Progression of liver disease was associated with improvement in blood glucose levels, with evidence of altered expression of gluconeogenic and glycolytic enzymes. However, these mice were able to mobilize stored glycogen in response to glucagon. Feeding F-IRKO and F-IR/IGFRKO mice a high-fat diet for 12 weeks accelerated the liver injury and normalization of blood glucose levels. Thus, severe fatty liver disease develops early in lipodystrophic mice and progresses to advanced nonalcoholic steatohepatitis with highly dysplastic liver nodules. The liver injury is propagated by lipotoxicity and is associated with improved blood glucose levels.