INSULIN/IGF-I REGULATION OF ADIPOCYTE DEVELOPMENT

The overall goal is to determine the biochemical and molecular processes
that govern the differentiation of 3T3-L1 adipocytes. An important initial
objective is to determine the mechanisms by which insulin-like growth
factor-I (IGF-I) and/or insulin participate in the triggering of the
adipocyte differentiation program and the modulation of the expression of
adipocyte-specific gene products. When hormones and growth factors are
removed from fetal calf serum the differentiation of 3T3-L1 cells into
adipocytes becomes highly dependent on either physiological concentrations
of IGF-I or a supraphysiological level of insulin. The unmasking of the
striking effect of IGF-I and the acquisition of experience and expertise in
recombinant DNA methodology in my laboratory over the past several years
now afford us the opportunities to (a) probe and elucidate fundamental
mechanisms in mammalian cell differentiation and (b) to obtain novel
information and insights regarding a possible central biological role for
IGF-I in the control of adipogenesis. We will approach these issues by
executing the following specific aims: (1) Clone cDNAs corresponding to
mRNAs that are induced at various stages of adipocyte development. (2) The
cDNA clones will be used to determine the sizes and kinetics of
accumulation of the IGF-I/insulin regulated mRNAs. (3) The mechanisms
responsible for differentiation-dependent and IGF-I/insulin regulated
accumulation of specific mRNAs will be determined. (4) IGF-I/insulin
regulated genes will be characterized. (5) Cis-acting regulatory sequences
that confer regulation by insulin/IGF-I will be identified and
characterized by the construction of fusion genes, transfection, expression
and mutagenesis. (6) IGF-I and insulin-binding studies will be performed
to correlate the level of occupancy of specific IGF-I and insulin receptors
with the degree and extent of regulation of specific genes.