A 400 bp PCR product generated with degenerate primers derived from the glu
agon-like peptide-1 receptor was used to screen a rat skeletal muscle cDNA
library. The predicted amino acid sequence oft he 978 bp open reading frame
has a predicted M-r of 35 804, an estimated isoelectric point (pI) of 5.31
and contains seven WD-40 repeats, which are common to G-protein beta subun
its (G beta). Although chemically and structurally similar to G beta subuni
ts, the predicted amino acid sequence, when compared with the previously cl
oned G beta isoforms, was found to be only 31-41% similar and thus was name
d G beta -like (G betaL, 'Gable'). Western blotting of whole-cell lysates a
nd immunoprecipitates of membrane and cytosolic fractions of HEK 293 cells
stably overexpressing a carboxy-terminal His-tagged G betaL indicates that
the protein is cytosolic and that it migrates at 42 kDa. A 4 kb transcript
was detected in all tissues surveyed by northern blotting; however, an addi
tional 2 kb transcript was detected in testis. Expression of G betaL mRNA w
as highest in the brain and testis, followed by lung, heart, kidney, skelet
al muscle, spleen and liver. In addition, reverse transcriptase/PCR showed
that several other tissues and cell lines express G betaL. The ubiquitous n
ature of the tissue expression pattern of G betaL is similar to thar of the
insulin receptor, which suggests that insulin may influence G betaL expres
sion. Indeed, G betaL protein and mRNA levels, in fully differentiated 3T3-
L1 adipocytes, were upregulated by insulin in a concentration-dependent fas
hion. These changes were highly sensitive to insulin stimulation, being min
imally affected by doses as low as 0.1 nM and maximally elevated by 1 nM do
ses. These data suggest that insulin regulates G betaL production and imply
that some of the actions of insulin may be mediated, in part, by this nove
l intracellular protein.