Identification of adipocyte adhesion molecule (ACAM), a novel CTX gene family, implicated in adipocyte maturation and development of obesity.
Few cell adhesion molecules have been reported to be expressed in mature adipocytes, and the significance of cell adhesion process in adipocyte biology is also unknown. In the present study, we identified ACAM (adipocyte adhesion molecule), a novel homologue of the CTX (cortical thymocyte marker in Xenopus) gene family. ACAM cDNA was isolated during PCR-based cDNA subtraction, and its mRNA was shown to be up-regulated in WATs (white adipose tissues) of OLETF (Otsuka Long-Evans Tokushima fatty) rats, an animal model for Type II diabetes and obesity. ACAM, 372 amino acids in total, has a signal peptide, V-type (variable) and C2-type (constant) Ig domains, a single transmembrane segment and a cytoplasmic tail. The amino acid sequence in rat is highly homologous to mouse (94%) and human (87%). ACAM mRNA was predominantly expressed in WATs in OLETF rats, and increased with the development of obesity until 30 weeks of age, which is when the peak of body mass is reached. Western blot analysis revealed that ACAM protein, approx. 45 kDa, was associated with plasma membrane fractions of mature adipocytes isolated from mesenteric and subdermal adipose deposits of OLETF rats. Up-regulation of ACAM mRNAs in obesity was also shown in WATs of genetically obese db/db mice, diet-induced obese ICR mice and human obese subjects. In primary cultured mouse and human adipocytes, ACAM mRNA expression was progressively up-regulated during differentiation. Several stably transfected Chinese-hamster ovary K1 cell lines were established, and the quantification of ACAM mRNA and cell aggregation assay revealed that the degree of homophilic aggregation correlated well with ACAM mRNA expression. In summary, ACAM may be the critical adhesion molecule in adipocyte differentiation and development of obesity.
Eguchi
Jun
J
Department of Medicine and Clinical Science, Okayama University Graduate School of Medicine and Dentistry, 2-5-1 Shikata-cho, Okayama 700-8558, Japan.
Wada
Jun
J
Hida
Kazuyuki
K
Zhang
Hong
H
Matsuoka
Takashi
T
Baba
Masako
M
Hashimoto
Izumi
I
Shikata
Kenichi
K
Ogawa
Norio
N
Makino
Hirofumi
H
D017667:Adipocytes / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D015815:Cell Adhesion Molecules / Q000502:physiology*; D002454:Cell Differentiation; D002462:Cell Membrane; D062727:Coxsackie and Adenovirus Receptor-Like Membrane Protein; D006224:Cricetinae; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D051379:Mice; D008813:Mice, Inbred ICR; D008969:Molecular Sequence Data; D005810:Multigene Family; D009765:Obesity / Q000503:physiopathology*; D000077205:Pioglitazone; D051381:Rats; D020334:Rats, Inbred OLETF; D011991:Receptors, Virus; D017386:Sequence Homology, Amino Acid; D045162:Thiazolidinediones / Q000494:pharmacology; D014018:Tissue Distribution; D015854:Up-Regulation
C568771:CLMP protein, human; C568772:CLMP protein, mouse; D015815:Cell Adhesion Molecules; C568773:Clmp protein, rat; D062727:Coxsackie and Adenovirus Receptor-Like Membrane Protein; D007004:Hypoglycemic Agents; D011991:Receptors, Virus; D045162:Thiazolidinediones; D000077205:Pioglitazone