Identification of novel membrane and secreted proteins upregulated during adipocyte differentiation

Adipose tissue is the largest organ in the body that secretes soluble proteins such as cytokines. A preadipocyte cell line 3T3-L1 has been widely used for investigations of mechanisms of adipocyte differentiation. 3T3-L1 cells convert to adipocytes in the presence of 1-methyl-3-isobutylxanthine, dexamethasone, and insulin. We screened a cDNA library derived from differentiated 3T3-L1 cells, using the SST-REX method (signal sequence trap by retrovirus-mediated expression screening method). Screening of 4 x 10(5) clones gave rise to 63 known and 8 novel clones. The known clones represented 28 independent proteins, 21 of which were secreted proteins and 7 were membrane proteins. The novel clones represented 7 independent proteins, 5 of which had no similarity to known proteins. Interestingly, most of these novel genes showed differentiation- and tissue-specific expression. The present results indicate that adipocytes specific genes or adipocyte differentiation-related genes encoding membrane and secreted proteins can be readily identified if signal sequence trap screening of differentiated adipocyte-derived cDNAs is done.