| Abstract: | Morphological studies indicate that basement membrane formation or maintenance can be achieved in cultures of thyroid cells. In the present investigation we have studied the biosynthesis of this extracellular matrix by differentiated porcine thyroid cells in culture. They were prepared by two procedures: (1) thyroid cells isolated by dispase digestion of the thyroid gland were maintained in serum-free medium on poly(L-lysine) coated dishes; (2) thyroid follicles released by collagenase treatment of the gland were isolated by differential filtration and cultured in suspension on agarose-coated dishes. In both cases, functional follicular-like structures were obtained as shown by their ability to organify Na125I and to respond to thyrotropin stimulation (250 microU/ml). After incubating the cells with radiolabeled proline or methionine, collagen synthesis was observed with the two types of culture, as shown by the formation of radioactive hydroxyproline and by the synthesis of peptides with electrophoretic properties identical to those of authentic collagen molecules and susceptible to collagenase. Besides variable amounts of type I and type III collagen-like peptides, significant proportions of labeled peptides migrated with type IV collagen chains and were precipitated by anti-type IV collagen antibody; thyrotropin had no significant effect either on the total collagen synthesis or on the relative amounts of the different collagen peptides. When thyroid cells were incubated with 35S]sulfate, a labeled glycosaminoglycan with chromatographic properties analogous to that of heparan sulfate could be obtained in both culture conditions; here again, no effect of thyrotropin was observed. The ability of differentiated porcine thyroid cells to synthesize basement membrane was suggested by their production of type IV collagen and heparan sulfate, two of its potential components. Thyrotropin, which drastically enhanced the functional property of the cells, did not seem to regulate this synthesis. |
