Collagen synthesis and deposition during mammary epithelial cell spreading on collagen gels

Mouse mammary epithelial cultivated on collagen gels demonstrate active spreading as the cells form monolayers. In this novel system, initiation of cell spreading is preceded by de novo synthesis of type IV collagen. The newly synthesized collagen is partitioned such that after 48 hr, approximately 24% is found in the culture medium, 35% is intracellular, and 41% is deposited in the extracellular matrix of the developing epithelium. Cultures deprived of serum failed to spread and to synthesize collagen. Proline analogues were shown to inhibit cell spreading and to suppress collagen synthesis in a dose-dependent manner. Cytochalasin D inhibition of F-actin elongation was shown to prevent cell spreading but not to suppress total collagen synthesis. During cytochalasin D treatment, inhibition of cell spreading was shown to result from failure to deposit or to maintain deposited collagen in the epithelium extracellular matrix. The data indicate that synthesis and extracellular deposition of a major basal lamina component (viz. type IV collagen) must precede and then accompany epithelial cell spreading in collagen gel culture. It is suggested that the microfilament apparatus, through some hypothetical integral membrane protein, can anchor extracellular type IV collagen, which then provides a necessary condition for cell spreading.