Hyperproinsulinaemia in obese fat/fat mice associated with a carboxypeptidase E mutation which reduces enzyme activity

Naggert, Jürgen Κ.; Fricker, Lloyd D.; Varlamov, Oleg; Nishina, Patsy M.; Rouillé, Yves; Steiner, Donald F.; Carroll, Raymond J.; Paigen, Beverly; Leiter, Edward H.

doi:10.1038/ng0695-135

Cited by 633 publications

(450 citation statements)

References 35 publications

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“…2C), accounting for 46.3 Ϯ 2.4% of total proinsulin-and insulin-related radioactivity. The presence of such a secretory product in cells after 150 min is suggestive of its being stored in granules of the regulated pathway, given that no such storage compartment exists for the constitutive pathway but indicates unusually slow proinsulin conversion in keeping with published data (20). The other minor radioactive peaks could correspond to arginine-extended forms of insulin or other proinsulin conversion intermediates.…”

Section: Resultssupporting

confidence: 55%

“…The pancreatic ␤-cells of these mice are clearly granulated but the content of the granules appears to be less dense (20), suggesting storage of proinsulin instead of mature insulin. Despite this observation, it has been suggested that proinsulin fails to be targeted to the regulated pathway in ␤-cells of these mice and that CPE is the sorting receptor not only for POMC but for other prohormones including proinsulin itself (18,19).…”

mentioning

confidence: 98%

“…Obese Cpe fat /Cpe fat mice suffer from hyperproinsulinemia associated with expression of a mutated CPE, which results in destruction of the CPE protein in the rough endoplasmic reticulum (20,21). The pancreatic ␤-cells of these mice are clearly granulated but the content of the granules appears to be less dense (20), suggesting storage of proinsulin instead of mature insulin.…”

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confidence: 99%

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Proinsulin Targeting to the Regulated Pathway Is Not Impaired in Carboxypeptidase E-deficientCpe /Cpe Mice

Irminger

Verchere

Meyer

et al. 1997

Journal of Biological Chemistry

103

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Sorting of proinsulin from the trans-Golgi network to secretory granules is critical for its conversion to insulin as well as for regulated insulin secretion. The proinsulin sorting mechanism is unknown. Recently, carboxypeptidase E (CPE) was proposed as a sorting receptor for prohormones. To know whether CPE is implicated in proinsulin sorting, pancreatic islets were isolated from CPE-deficient Cpe fat /Cpe fat mice and Cpe fat /؉ controls, pulse-labeled ([ 3 H]leucine), and then chased in basal medium (90 min) to examine constitutive secretion followed by medium with secretagogues (60 min) to stimulate regulated secretion. Secretion of labeled proinsulin via the constitutive pathway was <2% even in Cpe fat /Cpe fat islets. After a 150-min chase, only 13% of radioactivity remained as proinsulin in Cpe fat /؉ islets compared with 46% in Cpe fat /Cpe fat islets, reflecting slower conversion. Regulated secretion was stimulated to an equal extent from Cpe fat /؉ and Cpe fat /Cpe fat mice with 20% of the total content of labeled (pro)insulin released during the 60-min stimulatory period. It is concluded that in CPE-deficient Cpe fat / Cpe fat mice, proinsulin is efficiently routed to the regulated pathway and its release can be effectively stimulated by secretagogues. CPE is thus not essential for sorting proinsulin to granules.Proinsulin is directed to the regulated secretory pathway of the pancreatic ␤-cell and is converted to bioactive insulin in immature secretory granules (1). At least three enzymes are needed for generating native insulin, namely the conversion endoproteases PC1 (also known as PC3) and PC2 (2, 3) and carboxypeptidase E (also called carboxypeptidase H or CPE 1 ) for trimming residual basic C-terminal residues (4 -6). Correct targeting to secretory granules is essential for the cell to produce and store bioactive insulin, which can then be released upon stimulation of the ␤-cell by glucose or other secretagogues. One of the crucial steps in targeting takes place in the TGN (trans-Golgi network) (7). The proprotein must somehow be recognized selectively in the TGN and then be transferred to the immature secretory granules, instead of being released through the constitutive or default pathway (3).One hypothesis (reviewed in Ref.3) accounting for targeting within the TGN implicates a sorting receptor with a broad specificity in the TGN membrane, which recognizes a sorting domain and thereby binds proteins to be routed to the regulated pathway. Sorting domains have been reported for several prohormones including prosomatostatin (8, 9), chromogranin (10), and the basic proline-rich protein (11). An N-terminal sorting domain has been reported for proopiomelanocortin (POMC) (12, 13), although this is controversial (14). A putative C-terminal sorting domain has also recently been proposed for the prohormone convertase PC2 (15). There is not as yet any direct experimental evidence for a sorting domain for proinsulin, although the comparison of structural features of many prohormones suggests that a regio...

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Section: Resultssupporting

confidence: 55%

mentioning

confidence: 98%

mentioning

confidence: 99%

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Proinsulin Targeting to the Regulated Pathway Is Not Impaired in Carboxypeptidase E-deficientCpe /Cpe Mice

Irminger

Verchere

Meyer

et al. 1997

Journal of Biological Chemistry

103

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“…Several mutations in mouse genes that lead to obesity have recently been characterized at the molecular level (1)(2)(3)(4)(5)(6)(7)(8). Further analysis of these genes and the use of mouse lines with mutations in these genes provides an opportunity to identify new therapeutic targets for the treatment of human obesity.…”

mentioning

confidence: 99%

Combined effects of insulin treatment and adipose tissue-specific agouti expression on the development of obesity

Mynatt

Miltenberger

Klebig

et al. 1997

Proc. Natl. Acad. Sci. U.S.A.

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The agouti gene product is a secreted protein that acts in a paracrine manner to regulate coat color in mammals. Several dominant mutations at the agouti locus in mice cause the ectopic, ubiquitous expression of agouti, resulting in a condition similar to adult-onset obesity and non-insulin-dependent diabetes mellitus. The human agouti protein is 85% homologous to mouse agouti; however, unlike the mouse agouti gene, human agouti is normally expressed in adipose tissue. To address whether expression of agouti in human adipose tissue is physiologically relevant, transgenic mice were generated that express agouti in adipose tissue. Similar to most humans, these mice do not become obese or diabetic. However, we found that daily insulin injections significantly increased weight gain in the transgenic lines expressing agouti in adipose tissue, but not in nontransgenic mice. These results suggest that insulin triggers the onset of obesity and that agouti expression in adipose tissue potentiates this effect. Accordingly, the investigation of agouti's role in obesity and non-insulin-dependent diabetes mellitus in mice holds significant promise for understanding the pathophysiology of human obesity.

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“…Naggert et al [9] reported that mice homozygous for the fat mutation are obese and hyperglycemic. The mutation responsible for this phenotype was found in the CP-E gene.…”

Section: Introductionmentioning

confidence: 99%

Enzymic characterization of a novel member of the regulatory B-like carboxypeptidase with transcriptional repression function: stimulation of enzymic activity by its target DNA

Muise

1999

Biochemical Journal

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The adipocyte-enhancer binding protein (AEBP) 1 is a novel transcriptional repressor with carboxypeptidase (CP) activity. AEBP1 binds to a regulatory sequence (termed adipocyte enhancer 1, AE-1) located in the proximal promoter region of the adipose P2 (aP2) gene, which encodes the adipocyte fatty-acid binding protein. Sequence comparisons and kinetic studies using known carboxypeptidase substrates, activators and inhibitors have characterized AEBP1 as a member of the regulatory B-like CP family. Significantly, the inherent CP activity of AEBP1 is stimulated by the AE-1 sequence. Our results indicate that AEBP1 is activated by a novel mechanism, wherby the direct binding of DNA enhances its protease activity. These results represent the first demonstration of DNA-mediated regulation of CP activity.

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Hyperproinsulinaemia in obese fat/fat mice associated with a carboxypeptidase E mutation which reduces enzyme activity

Cited by 633 publications

References 35 publications

Proinsulin Targeting to the Regulated Pathway Is Not Impaired in Carboxypeptidase E-deficientCpe /Cpe Mice

Proinsulin Targeting to the Regulated Pathway Is Not Impaired in Carboxypeptidase E-deficientCpe /Cpe Mice

Combined effects of insulin treatment and adipose tissue-specific agouti expression on the development of obesity

Enzymic characterization of a novel member of the regulatory B-like carboxypeptidase with transcriptional repression function: stimulation of enzymic activity by its target DNA

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