CELLULAR ACTIONS OF TRANSFORMING GROWTH FACTORS

Since the discovery that specific polypeptide factors termed transforming
growth factors (TGFs) were able to confer the transformed phenotype to
otherwise normal cells, elucidation of their mechanisms of action has been
a goal in cancer research. Over the past few years a great deal of effort
has been expended in the isolation and purification of TGFs, since
mechanistic studies require the use of purified molecules. Recently,
highly purified preparations of TGFs (TGF-alpha and TGF-beta) have been
obtained, thereby paving the way for attempts to determine their mechanisms
of action and the set of specific cellular responses which they elicit.
This research intends to address questions regarding the identity of
specific cell-surface TGF receptors, their involvement in mediating
TGF-associated responses, and the specific intracellular consequences of
TGF action. Efforts will continue to purify TGF-alpha and TGF-beta from
rat fetuses, utilizing chromatography, isoelectric focusing, and HPLC
methods. Purified TGFs will be iodinated in order to elucidate their
characteristics of binding to cell surfaces of nontransformed and
transformed mouse and rat cells. The characteristics of endocytosis and
intracellular processing of 125 I-TGFs will be investigated, with emphasis
on intracellular sites of TGF processing. Photoaffinity labeling of TGF
receptors will be employed to demonstrate their molecular weight
characteristics and to determine the intracellular localization of
GF-receptor complexes. Clones of cDNAs homologous to genes induced by
TGF-alpha and TGF-beta in mouse and rat cells will be obtained in plasmid
and phage vectors. These cDNA clones will be employed to determine whether
TGF-alpha and TGF-beta induce the same or different gene products and if
EGF-\and TGF-alpha induce similar gene products. The ability of the tumor
promoter TPA to induce gene products similar to those induced by TGFs will
also be determined. The endogenous level of expression of TGF-induced
genes in transformed cells will be compared to the level found in normal
cells. Finally, the ability of lysosomotropic agents to inhibit
TGF-induced expression of specific gene products will be investigated. (J)