Identification and characterization of a transcript for a novel Rac GTPase-activating protein in terminally differentiating 3T3-L1 adipocytes

Using differential display, we sought to identify novel genes expressed in the early stages of 3T3-L1 adipocyte differentiation. A gene which we have named "band25" was identified, and a full-length cDNA sequence was assemble d. Sequence analysis revealed that the 2842-bp cDNA encodes a putative 628- amino acid protein product, which is a member of the GTPase-activating prot ein (GAP) family. This gene may be the murine homolog of the human MgcRacGA P protein, which was identified in male germ cells. Other closely related p roteins include the Drosophila protein Rotund, several chimerins, and the h uman breakpoint cluster region (Bcr) protein. These GAP proteins all specif ically inactivate Rac, a member of the Pas-like family of proteins. A conse nsus sequence for a diacyl glycerol/phorbol eater-binding domain was also f ound in the Band25 sequence, The expression of band25 mRNA is regulated dur ing the differentiation of both adipocytes and myoblasts, Its mRNA was show n to be expressed at a low level in confluent 3T3-L1 preadipocytes and in d ifferentiated 3T3-L1 adipocytes. Expression of band25 was increased 15.5 fo ld by 24 h after the induction of differentiation, when 3T3-L1 cells underg o several rounds of postconfluent cell division. Expression was also high i n growing 3T3-L1 and C2C12 cells but decreased progressively as C2C12 cells underwent differentiation. These observations suggest that the expression of band25 is growth regulated and that the protein could play a role in the regulation of growth-related processes.