Identification of a novel integral plasma membrane protein induced during adipocyte differentiation

Abstract

Adipocyte differentiation is co-ordinately regulated by several transcription factors and is accompanied by changes in the expression of a variety of genes. Using mRNA differential display analysis, we have isolated a novel mRNA, DD16, specifically induced during the course of adipocyte differentiation. DD16 mRNAs are present in several tissues, but among the tissues tested, a remarkably higher level of expression was found in white adipose tissue. The DD16 cDNA encoded a polypeptide of 415 amino acids containing a single N-glycosylation site and an N-terminal hydrophobic stretch of 19 amino acids forming a transmembrane segment, indicating that DD16 is a glycosylated membrane-bound protein. Polyclonal antibodies raised against the DD16 peptide detected immunoreactive DD16 in membrane fractions, notably the plasma membrane. Association of DD16 with the plasma membrane was further confirmed by biotinylation studies of cell surface proteins, suggesting that DD16 is an integral plasma membrane protein. Therefore we propose to give DD16 the name APMAP (Adipocyte Plasma Membrane-Associated Protein). Although the biological function of this polypeptide is presently unknown, our data suggest that APMAP may function as a novel protein involved in the cross-talk of mature adipocytes with the environment.

The adipocyte differentiation protein APMAP is an endogenous suppressor of Aβ production in the brain

“…RTN4 encodes for the myelin-associated multi-pass membrane protein reticulon-4 (Nogo), a neurite outgrowth inhibitor limiting plasticity in the healthy adult brain and neuronal regeneration during brain injury (reviewed in 13 ). APMAP encodes for a 415-amino-acid long single-pass type-II glycosylated membrane protein that is implicated in the regulation of white adipose tissue differentiation ( 14 , 15 ). TSPAN6 belongs to the tetraspanin superfamily of multi-pass membrane proteins interacting with multiple immune-related molecules, including immune receptors, integrins, signaling molecules and functioning as important immune response modulators ( 16 ).…”

Reconstruction of gene association network reveals a transmembrane protein required for adipogenesis and targeted by PPARγ

“…Sequence analyses of the RIKEN clone showed that this probe represents a protein annotated as APMAP. It was previously shown to be expressed during adipogenesis in 3T3-L1 cells [24,20,11]. However, the physiological relevance and precise role during adipogenesis remained elusive.…”

“…The C-terminal domain of APMAP is required for the function of APMAP during adipogenesis As we and others have showed, APMAP is a transmembrane protein (41-60 AA) [24] with the C-terminal domain predicted to be a six-bladed b-propeller [34]. To assess whether the six-bladed b-propeller is necessary for the function of APMAP in adipogenesis, APMAP-silenced cells were stably transduced with two truncated APMAP constructs.…”

“…Only recently, several other classes of genes encoding factors not previously recognized in developmental regulation have been shown to be implicated in adipocyte differentiation. This includes classic enzymes such as retinol saturase, the enzymatic activity of which has been shown to be required for adipogenesis (24), and xanthine oxidoreductase which is necessary for full adipocyte development and PPARc2 expression in mice (25). Further examples include steroyl-CoA desaturase 2 (SCD2), as a regulator of adipogenesis (26).…”

DecreasedO-GlcNAcylation of the key proteins in kinase and redox signalling pathways is a novel mechanism of the beneficial effect of α-lipoic acid in diabetic liver

“…Nuclear and cytosol proteins were prepared from the liver tissue (100 mg/sample) using the ProteoJET Cytoplasmic and Nuclear Protein Extraction Kit (Fermentas), according to the manufacturer's instructions. Mitochondria were isolated by differential centrifugation (30) .…”