Hypothalamic ER–associated degradation regulates POMC maturation, feeding, and age-associated obesity
Geun Hyang Kim, Guojun Shi, Diane R.M. Somlo, Leena Haataja, Soobin Song, Qiaoming Long, Eduardo A. Nillni, Malcolm J. Low, Peter Arvan, Martin G. Myers Jr., Ling Qi
Geun Hyang Kim, Guojun Shi, Diane R.M. Somlo, Leena Haataja, Soobin Song, Qiaoming Long, Eduardo A. Nillni, Malcolm J. Low, Peter Arvan, Martin G. Myers Jr., Ling Qi
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Research Article Cell biology Metabolism

Hypothalamic ER–associated degradation regulates POMC maturation, feeding, and age-associated obesity

Abstract

Pro-opiomelanocortin (POMC) neurons function as key regulators of metabolism and physiology by releasing prohormone-derived neuropeptides with distinct biological activities. However, our understanding of early events in prohormone maturation in the ER remains incomplete. Highlighting the significance of this gap in knowledge, a single POMC cysteine-to-phenylalanine mutation at position 28 (POMC-C28F) is defective for ER processing and causes early onset obesity in a dominant-negative manner in humans through an unclear mechanism. Here, we report a pathologically important role of Sel1L-Hrd1, the protein complex of ER-associated degradation (ERAD), within POMC neurons. Mice with POMC neuron–specific Sel1L deficiency developed age-associated obesity due, at least in part, to the ER retention of POMC that led to hyperphagia. The Sel1L-Hrd1 complex targets a fraction of nascent POMC molecules for ubiquitination and proteasomal degradation, preventing accumulation of misfolded and aggregated POMC, thereby ensuring that another fraction of POMC can undergo normal posttranslational processing and trafficking for secretion. Moreover, we found that the disease-associated POMC-C28F mutant evades ERAD and becomes aggregated due to the presence of a highly reactive unpaired cysteine thiol at position 50. Thus, this study not only identifies ERAD as an important mechanism regulating POMC maturation within the ER, but also provides insights into the pathogenesis of monogenic obesity associated with defective prohormone folding.

Authors

Geun Hyang Kim, Guojun Shi, Diane R.M. Somlo, Leena Haataja, Soobin Song, Qiaoming Long, Eduardo A. Nillni, Malcolm J. Low, Peter Arvan, Martin G. Myers Jr., Ling Qi

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Figure 7

Pathogenic POMC-C28F mutation is completely rescued by an intragenic suppressor mutation C50S.

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Pathogenic POMC-C28F mutation is completely rescued by an intragenic sup...
(A) Schematic diagram showing the sequence and positions of Cys residues in POMC-WT, C28F, and C28F/C50S. (B) Western blot analyses of POMC-Flag immunoprecipitates in HEK293T cells transfected with a combination of Myc- or Flag-tagged POMC under nonreducing (–β-ME) and reducing (+β-ME) SDS-PAGE. Two panels were from the same experiment at the same exposure time, with the irrelevant lanes in the middle cut off. (C) Sucrose gradient fractionation and Western blot analysis of HEK293T cells expressing POMC-C28F or -C28F/C50S under nonreducing (–β-ME) and reducing (+ β-ME) SDS-PAGE. (D) Metabolic labeling experiments to visualize the maturation of nascent POMC in HEK293T cells transfected with POMC-Myc. Cells were pulsed for 30 minutes and chased for the indicated times, followed by immunoprecipitation with anti-Myc agarose beads and separation on SDS-PAGE gels under nonreducing or reducing conditions and autoradiography. (E) Representative confocal images of POMC in POMC-transfected WT N2a cells. White arrows point to secreted POMC in granules, while yellow arrows point to perinuclear POMC, possibly in the form of aggregates. KDEL marks the ER. Representative data from at least 2 independent experiments shown.