SummaryThermogenesis in brown adipose tissue (BAT) is fundamental to energy balance and is also relevant for humans. Bone morphogenetic proteins (BMPs) regulate adipogenesis, and, here, we describe a role for BMP8B in the direct regulation of thermogenesis. BMP8B is induced by nutritional and thermogenic factors in mature BAT, increasing the response to noradrenaline through enhanced p38MAPK/CREB signaling and increased lipase activity. Bmp8b−/− mice exhibit impaired thermogenesis and reduced metabolic rate, causing weight gain despite hypophagia. BMP8B is also expressed in the hypothalamus, and Bmp8b−/− mice display altered neuropeptide levels and reduced phosphorylation of AMP-activated protein kinase (AMPK), indicating an anorexigenic state. Central BMP8B treatment increased sympathetic activation of BAT, dependent on the status of AMPK in key hypothalamic nuclei. Our results indicate that BMP8B is a thermogenic protein that regulates energy balance in partnership with hypothalamic AMPK. BMP8B may offer a mechanism to specifically increase energy dissipation by BAT.

We performed a systematic mapping of interaction domains on COP I subunits to gain novel insights into the architecture of coatomer. Using the two-hybrid system, we characterize the domain structure of the a-, b ¢-, e-COP and b-, g-, d-, z-COP coatomer subcomplexes and identify links between them that contribute to coatomer integrity. Our results demonstrate that the domain organization of the b-, g-, d-, z-COP subcomplex and AP adaptor complexes is related. Through in vivo analysis of a-COP truncation mutants, we characterize distinct functional domains on a-COP. Its N-terminal WD40 domain is dispensable for yeast cell viability and overall coatomer function, but is required for KKXX-dependent traf®cking. The last~170 amino acids of a-COP are also nonessential for cell viability, but required for e-COP incorporation into coatomer and maintainance of normal e-COP levels. Further, we demonstrate novel direct interactions of coatomer subunits with regulatory proteins: b ¢-and g-COP interact with the ARF-GTP-activating protein (GAP) Glo3p, but not Gcs1p, and b-and e-COP interact with ARF-GTP. Glo3p also interacts with intact coatomer in vitro.

Coatomer is required for the retrieval of proteins from an early Golgi compartment back to the endoplasmic reticulum. The WD40 domain of ␣-COP is required for the recruitment of KKTN-tagged proteins into coatomer-coated vesicles. However, lack of the domain has only minor effects on growth in yeast. Here, we show that the WD40 domain of ␤ -COP is required for the recycling of the KTKLL-tagged Golgi protein Emp47p. The protein is degraded more rapidly in cells with a point mutation in the WD40 domain of ␤ -COP (sec27-95) or in cells lacking the domain altogether, whereas a point mutation in the Clathrin Heavy Chain Repeat (sec27-1) does not affect the turnover of Emp47p. Lack of the WD40 domain of ␤ -COP has only minor effects on growth of yeast cells; however, absence of both WD40 domains of ␣-and ␤ -COP is lethal. Two hybrid studies together with our analysis of the maturation of KKTN-tagged invertase and the turnover of Emp47p in ␣-and ␤ -COP mutants suggest that the two WD40 domains of ␣-and ␤ -COP bind distinct but overlapping sets of di-lysine signals and hence both contribute to recycling of proteins with di-lysine signals.