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Mol. Cell. Biol., Jun 1995, 3398-3404, Vol 15, No. 6
PY Desprez, E Hara, MJ Bissell and J Campisi
Cell proliferation and differentiation are precisely coordinated during the
development and maturation of the mammary gland, and this balance
invariably is disrupted during carcinogenesis. Little is known about the
cell-specific transcription factors that regulate these processes in the
mammary gland. The mouse mammary epithelial cell line SCp2 grows well under
standard culture conditions but arrests growth, forms alveolus-like
structures, and expresses beta-casein, a differentiation marker, 4 to 5
days after exposure to basement membrane and lactogenic hormones
(differentiation signals). We show that this differentiation entails a
marked decline in the expression of Id-1, a helix-loop-helix (HLH) protein
that inactivates basic HLH transcription factors in other cell types. SCp2
cells stably transfected with an Id-1 expression vector grew more rapidly
than control cells under standard conditions, but in response to
differentiation signals, they arrested growth and formed three-dimensional
structures similar to those of control cells. Id-1-expressing cells did
not, however, express beta-casein. Moreover, 8 to 10 days after receiving
differentiation signals, they lost three- dimensional organization, invaded
the basement membrane, and then resumed growth. SCp2 cells expressing an
Id-1 antisense vector grew more slowly than controls; in response to
differentiation signals, they remained stably growth arrested and fully
differentiated, as did control cells. We suggest that Id-1 renders cells
refractory to differentiation signals and receptive to growth signals by
inactivating one or more basic HLH proteins that coordinate growth and
differentiation in the mammary epithelium.
Copyright © 1995, American Society for Microbiology
Suppression of mammary epithelial cell differentiation by the helix- loop-helix protein Id-1
Department of Cancer Biology, Lawrence Berkeley Laboratory, University of California, Berkeley 94720, USA.
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