Metabolic fate of the major cell surface protein of normal human fibroblasts

The major cell surface protein of a strain of human fetal lung fibroblasts is a 220,000 dalton glycoprotein termed fibronectin. Fibronectin is released from fibroblasts into the culture medium with a half-time of about 25 hours. The release occurs with an initial (0–3 hours) rapid phase followed by a second (3–48 hours) slower phase. Release of fibronectin occurs in a stoichiometric fashion. All of the fibronectin released from the cells is quantitatively recovered from the culture media as a similar sized soluble glycoprotein. Thus, release of fibronectin from normal human fibroblasts results from mechanisms other than extensive degradation of the protein.