Fig. 4.

Nidogen-1 does not signal for β-casein expression by itself. SCp2 cells were cultured on tissue culture plastic and overlaid for 4 days with medium containing lactogenic hormones and the indicated amounts of different soluble ECM components marked on the right. Cell lysates were resolved by SDS-PAGE and immunoblotted for β-casein (position marked by arrowhead). rBM, but not nidogen-1 or fibronectin, induced β-casein expression. To determine whether the absence of nidogen-1 signaling was due to the inability of nidogen-1 to induce SCp2 cell rounding, cells were cultured on anti-adhesive polyHEMA-coated tissue culture plastic and overlaid for 4 days with medium containing lactogenic hormones and the indicated amounts of nidogen-1 (lane marked nidogen-1/polyHEMA). Even under these conditions, β-casein was still absent.