The 5 ' stem-loop regulates expression of collagen alpha 1(I) mRNA in mouse fibroblasts cultured in a three-dimensional matrix

The stability of collagen alpha 1(I) mRNA is regulated by its 5' stem-loop, which binds a cytoplasmic protein in a cap-dependent manner, and its 3'-un translated region (UTR), which binds alpha CP, When cultured in a three-dim ensional gel composed of type I collagen, mouse fibroblasts had decreased c ollagen alpha 1(I) mRNA steady-state levels, which resulted from a decrease d mRNA half-life, In cells cultured in gel, hybrid mouse-human collagen alp ha 1(I) mRNA with a wild-type 5' stem-loop decayed faster than the same mRN A with a mutated stem-loop. When the 5' stem-loop was placed in a heterolog ous mRNA, the mRNA accumulated to a lower level in cells grown in gel than in cells grown on plastic. This suggests that the 5' stem-loop down-regulat es collagen alpha 1(I) mRNA, Protein binding to the 5' stem-loop was reduce d in cells grown in gel, which was associated with destabilization of the c ollagen alpha 1(I) mRNA, In addition to the binding of a cytoplasmic protei n, there was also a nuclear binding activity directed to the collagen alpha 1(I) 5' stem-loop. The nuclear binding was increased in cells grown in gel , suggesting that it may negatively regulate expression of collagen alpha 1 (I) mRNA, Binding of alpha CP, a protein involved in stabilization of colla gen alpha 1(I) mRNA, was unchanged by the culture conditions.