OVEREXPRESSION OF PTEN GENE INCREASES INS2 GENE MRNA EXPRESSION, NOT INS1 GENE MRNA EXPRESSION, IN INSULINOMA CELL LINE RIN-5F

Objective

One functional neuroendocrine tumor that causes hypoglycemia due to inappropriately high insulin production is an insulinoma. In rats, two genes coding for insulin, insulin 1 (Ins1) and insulin 2 (Ins2) are found on chromosome 1. Ins1 was produced from an Ins2 transcript, and it was inserted into the genome via an RNA-mediated duplication-transposition event, according to some structural feature analyses.

Methods

In this study, the author has looked at how overexpression of the PTEN gene in the insulinoma cell line Rin-5F affects the expression of the insulin genes, Ins 1 and Ins 2.

Results

In the insulinoma cell line, overexpression of the PTEN gene boosts Ins2 gene mRNA expression but not Ins1 gene mRNA expression. It has been reported that PTEN upregulates insulin signaling by increasing insulin receptor substrate (IRS)-2 mRNA levels. Also, PTEN has been reported to be secreted in exosomes and thereafter, into extracellular space.

Conclusions

The present study suggested that overexpression of PTEN might induce the increasing Ins 2 gene expression, one of the phosphorylated genes against the IRS-2 through the insulin/IGF-1 receptor. Our knowledge of the molecular pathways of PTEN relating the synthesis of insulin has been increased by the present study.

OVEREXPRESSION OF PDX-1 GENE INCREASES INS1 GENE mRNA EXPRESSION, NOT INS2 GENE mRNA EXPRESSION, IN INSULINOMA CELL LINE RIN-5F

OBJECTIVE

Insulinoma is one of the functional neuroendocrine tumors, which induce hypoglycemia caused by inadequate high secretion of insulin. In rats, two genes coding for insulin, insulin 1 (Ins1) and insulin 2 (Ins2) are found on chromosome 1. Some structural feature studies have shown that Ins1 was generated from a transcript of Ins2 and was inserted into the genome by an RNA-mediated duplication-transposition event.

METHODS

In this study, the author has investigated how the expression of insulin genes, Ins 1 and Ins2, are altered by Pdx-1 gene overexpression in the insulinoma cell line, Rin-5F.

RESULTS

Overexpression of the Pdx-1 gene increases Ins1 gene mRNA expression, not Ins2 gene mRNA expression, in the insulinoma cell line. Thus, levels of the rat insulin 1 and insulin 2 peptides may be changed under specific conditions.

CONCLUSIONS

This is the first report that Ins1, but not Ins2, is significantly increased by Pdx-1 gene overexpression in the insulinoma cell line. This could indicate more research and analysis of insulinoma tumorigenesis and Pdx-1 gene expression.

Methylation of insulin DNA in response to proinflammatory cytokines during the progression of autoimmune diabetes in NOD mice

AIMS/HYPOTHESIS

Type 1 diabetes is caused by the immunological destruction of pancreatic beta cells. Preclinical and clinical data indicate that there are changes in beta cell function at different stages of the disease, but the fate of beta cells has not been closely studied. We studied how immune factors affect the function and epigenetics of beta cells during disease progression and identified possible triggers of these changes.

METHODS

We studied FACS sorted beta cells and infiltrating lymphocytes from NOD mouse and human islets. Gene expression was measured by quantitative real-time RT-PCR (qRT-PCR) and methylation of the insulin genes was investigated by high-throughput and Sanger sequencing. To understand the role of DNA methyltransferases, Dnmt3a was knocked down with small interfering RNA (siRNA). The effects of cytokines on methylation and expression of the insulin gene were studied in humans and mice.

RESULTS

During disease progression in NOD mice, there was an inverse relationship between the proportion of infiltrating lymphocytes and the beta cell mass. In beta cells, methylation marks in the Ins1 and Ins2 genes changed over time. Insulin gene expression appears to be most closely regulated by the methylation of Ins1 exon 2 and Ins2 exon 1. Cytokine transcription increased with age in NOD mice, and these cytokines could induce methylation marks in the insulin DNA by inducing methyltransferases. Similar changes were induced by cytokines in human beta cells in vitro.

CONCLUSIONS/INTERPRETATION

Epigenetic modification of DNA by methylation in response to immunological stressors may be a mechanism that affects insulin gene expression during the progression of type 1 diabetes.

Structural basis for the ATP-independent proteolytic activity of LonB proteases and reclassification of their AAA+ modules

Lon proteases degrade defective or denature proteins as well as some folded proteins for the control of cellular protein quality. There are two types of Lon proteases, LonA and LonB. Each consists of two functional components: a protease component and an ATPase associated with various cellular activities (AAA+ module). Here, we report the 2.03 -resolution crystal structure of the isolated AAA+ module (iAAA+ module) of LonB from Thermococcus onnurineus NA1 (TonLonB). The iAAA+ module, having no bound nucleotide, adopts a conformation virtually identical to the ADP-bound conformation of AAA+ modules in the hexameric structure of TonLonB; this provides insights into the ATP-independent proteolytic activity observed in a LonB protease. Structural comparison of AAA+ modules between LonA and LonB revealed that the AAA+ modules of Lon proteases are separated into two distinct clades depending on their structural features. The AAA+ module of LonB belongs to the -H2 & Ins1 insert clade (HINS clade)- defined for the first time in this study, while the AAA+ module of LonA is a member of the HCLR clade.

Deletion of retinoic acid receptor β (RARβ) impairs pancreatic endocrine differentiation

All-trans retinoic acid (RA) signals via binding to retinoic acid receptors (RARs α, β, and γ). RA directly influences expression of Pdx1, a transcription factor essential for pancreatic development and beta-cell (β-cell) maturation. In this study we follow the differentiation of cultured wild-type (WT) vs. RARβ knockout (KO) embryonic stem (ES) cells into pancreatic islet cells. We found that RARβ KO ES cells show greatly reduced expression of some important endocrine markers of differentiated islet cells, such as glucagon, islet amyloid polypeptide (Iapp), and insulin 1 (Ins1) relative to WT. We conclude that RARβ activity is essential for proper differentiation of ES cells to pancreatic endocrine cells.