A. Shisheva et al., CLONING, CHARACTERIZATION, AND EXPRESSION OF A NOVEL GDP DISSOCIATIONINHIBITOR ISOFORM FROM SKELETAL-MUSCLE, Molecular and cellular biology, 14(5), 1994, pp. 3459-3468
Cellular mechanisms for controlling membrane trafficking appear to inv
olve small GTP-binding proteins such as the Rab proteins. Rab function
is regulated by GDP dissociation inhibitor (GDI), which releases Rab
proteins from membranes and inhibits GDP dissociation. Here we report
the isolation of a full-length cDNA encoding a novel GDI isoform of 44
5 amino acids (GDI-2) with a deduced molecular weight of 50,649 from m
ouse skeletal muscle. Full-length and partial cDNA clones encoding a p
reviously reported GDI protein (GDI-1) were also isolated from cDNA li
braries prepared from rat brain and mouse skeletal muscle, respectivel
y. The degree of deduced amino acid sequence identity between mouse GD
I-2 and our mouse GDI-1 cDNA clone is 86%. Northern (RNA blot) analysi
s revealed that in human tissues, bath GDI-1 and GDI-2 transcripts wer
e abundant in brain, skeletal muscle, and pancreas but were weakly exp
ressed in heart and liver. GDI-1 mRNA was expressed in kidney, whereas
GDI-2 was almost absent, while in lung the relative amounts of these
mRNA species were reversed. Specific antibodies against mouse GDI-1 an
d GDI-2 based on unique peptide sequences in the proteins were raised.
Differentiation of 3T3-L1 fibroblasts into highly insulin-responsive
adipocytes was accompanied by large increases in both mRNA and protein
levels of GDI-1 and GDI-2. GDI-1 and GDI-2 expressed as glutathione S
-transferase fusion proteins were both able to solubilize the membrane
-bound forms of Rab4 and Rab5 in a GDP/GTP-dependent manner. Taken tog
ether, these data demonstrate that the protein products of at least tw
o genes regulate the membrane dynamics of Rab proteins in mice.