This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rau, H. Articles by Whitehead, J. P. Search for Related Content PubMed PubMed Citation Articles by Rau, H. Articles by Whitehead, J. P. Pubmed/NCBI databases Substance via MeSH

Truncated Human Leptin (133) Associated with Extreme Obesity Undergoes Proteasomal Degradation after Defective Intracellular Transport¹

Departments of Medicine (H.R., S.O.R., J.P.W.) and Clinical Biochemistry (H.R., B.J.R., S.O.R., J.P.W.), University of Cambridge, Addenbrooke’s Hospital, Cambridge, CB2 2QR, United Kingdom

Address all correspondence and requests for reprints to: Prof. Stephen O’Rahilly, Departments of Medicine and Clinical Biochemistry, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 2QR, United Kingdom. E-mail: sorahill{at}hgmp.mrc.ac.uk

We recently described a homozygous frameshift mutation in the human leptin (ob) gene associated with undetectable serum leptin and extreme obesity in two individuals (1). This represented the first identified genetic cause of morbid obesity in humans. Preliminary data suggested a defect in the secretion of this truncated (133) mutant leptin. In the present investigation, we have examined the mechanisms underlying the defective secretion of the 133 leptin in transient transfection studies in Chinese hamster ovary and monkey kidney epithelium cells. Consistent with our previous observations, only immunoreactive wild-type (wt) leptin was secreted. In pulse chase experiments, intracellular wt leptin levels decreased, concomitant with secretion into the medium. In contrast, though immunoreactive 133 leptin disappeared from cell lysates with kinetics similar to those of wt leptin (half-life, 45 min), it was not detected in the medium. Inhibition of the proteasome, using the inhibitor clastolactacystin ß-lactone, led to a significant increase in the intracellular levels of 133 leptin, indicating a role for the proteasome in the degradation pathway. Although intracellular immunoprecipitated wt and 133 leptin levels were comparable, analysis of total cell lysates revealed a 7-fold increase in total intracellular 133 leptin, compared with wt leptin. Size-exclusion membrane filtration demonstrated that intracellular 133 leptin accumulated in an aggregated form, presumably as a result of misfolding in the endoplasmic reticulum. Consistent with this, an endoplasmic reticulum-like localization for 133 leptin was detected by immunofluorescence microscopy. In conclusion, the 133 mutant leptin is not secreted but accumulates intracellularly, as a consequence of misfolding/aggregation, and is subsequently degraded by the proteasome. These studies further define the genotype/phenotype correlation in this paradigmatic case of human leptin deficiency.

This article has been cited by other articles:

				M.-J. Lee and S. K. Fried Integration of hormonal and nutrient signals that regulate leptin synthesis and secretion Am J Physiol Endocrinol Metab, June 1, 2009; 296(6): E1230 - E1238. [Abstract] [Full Text] [PDF]

				I S. Farooqi and S. O'Rahilly Leptin: a pivotal regulator of human energy homeostasis Am. J. Clinical Nutrition, March 1, 2009; 89(3): 980S - 984S. [Abstract] [Full Text] [PDF]

				C. R. LaPensee, E. R. Hugo, and N. Ben-Jonathan Insulin Stimulates Interleukin-6 Expression and Release in LS14 Human Adipocytes through Multiple Signaling Pathways Endocrinology, November 1, 2008; 149(11): 5415 - 5422. [Abstract] [Full Text] [PDF]

				V. E F Crowley Overview of human obesity and central mechanisms regulating energy homeostasis Ann Clin Biochem, May 1, 2008; 45(3): 245 - 255. [Abstract] [Full Text] [PDF]

				L. G. Bermudez-Humaran, S. Nouaille, V. Zilberfarb, G. Corthier, A. Gruss, P. Langella, and T. Issad Effects of Intranasal Administration of a Leptin-Secreting Lactococcus lactis Recombinant on Food Intake, Body Weight, and Immune Response of Mice Appl. Envir. Microbiol., August 15, 2007; 73(16): 5300 - 5307. [Abstract] [Full Text] [PDF]

				M.-J. Lee and S. K. Fried Multilevel regulation of leptin storage, turnover, and secretion by feeding and insulin in rat adipose tissue J. Lipid Res., September 1, 2006; 47(9): 1984 - 1993. [Abstract] [Full Text] [PDF]

				I.S. Farooqi and S. O'Rahilly Monogenic Human Obesity Syndromes Recent Prog. Horm. Res., January 1, 2004; 59(1): 409 - 424. [Abstract] [Full Text]

				S. O'Rahilly, I. S. Farooqi, G. S. H. Yeo, and B. G. Challis Minireview: Human Obesity--Lessons from Monogenic Disorders Endocrinology, September 1, 2003; 144(9): 3757 - 3764. [Abstract] [Full Text] [PDF]

				P. Mancuso, A. Gottschalk, S. M. Phare, M. Peters-Golden, N. W. Lukacs, and G. B. Huffnagle Leptin-Deficient Mice Exhibit Impaired Host Defense in Gram-Negative Pneumonia J. Immunol., April 15, 2002; 168(8): 4018 - 4024. [Abstract] [Full Text] [PDF]