Mr 205,000 sulfoglycoprotein in extracellular matrix of mouse fibroblast cells is immunologically related to high molecular weight microtubule-associated proteins.

Rabbit antibodies raised against microtubule-associated protein 1 (MAP-1) from hog brain were found to crossreact with extracellular matrix components of mouse BALB/c 3T3 cell cultures. As shown by immunofluorescence microscopy of confluent cell cultures, the extracellular MAP-related antigen was located on dense fibrillar network arrays underlying and surrounding the cells. The immunoreactive material was sensitive to trypsin but resistant to collagenase. The microtubule-disrupting drug colcemid had no visible effect on the morphology of the anti-MAP-stained network, whereas treatment with cytochalasin B provoked its abolishment. Simian virus 40-transformed BALB/c 3T3 cells expressed considerably less extracellular antigen than did the nontransformed cells. After in vivo radiolabeling of BALB/c 3T3 cells, a secreted polypeptide of Mr 205,000 was isolated by immuno-precipitation from culture media as well as from cell-free extracellular matrices. This antigen was identified as a sulfoglycoprotein, noncollageneous in nature, that undergoes intermolecular disulfide bonding. Anti-MAP-1 antibodies affinity-purified on the extracellular Mr 205,000 protein were immunoreactive with MAP-1 and MAP-2 from brain and decorated cytoplasmic microtubules as demonstrated by immunoblotting and immunofluorescence microscopy. Thus, a structural relationship between cytoskeletal and extracellular polypeptides is demonstrated.