High‐molecular‐weight Fibronectin Synthesized by Adenoid Cystic Carcinoma Cells of Salivary Gland Origin

To understand the morphogenesis of characteristic cribriform structures and the frequent invasion of salivary adenoid cystic carcinomas (ACC) along such basement membrane‐rich structures as peripheral nerves, we have isolated fibronectin (FN) from the culture media of ACC3 cells established from a parotid ACC and characterized its glycosylation and alternative splicing status. FN isolated from ACC3 cells (ACC‐FN) showed a molecular mass of 315 kDa in SDS‐PAGE and was less heterogeneous and larger than plasma FN (pFN) or FNs from other cell sources. Differential enzymatic treatments of immunoprecipitated ACC‐FN with neuraminidase, peptide‐N‐glycosidase F and endo‐α‐N‐acetylgalactosaminidase revealed that ACC‐FN was composed of a polypeptide chain of 270 kDa, with 10 kDa each of N‐linked and O‐linked oligosaccharide chains. Reverse transcription polymerase chain reaction (RT‐PCR), in‐situ hybridization, and immunofluorescence studies showed that most ACC‐FNs contained ED‐A, ED‐B and IIICS regions in the molecules. This alternative splicing status of ACC‐FN seemed to contribute to its less heterogeneous and larger molecular form. Cell attachment assay demonstrated that ACC‐FN was more potent than pFN in adhesion of ACC3 cells. The results indicated that ACC‐FN may function as a substrate for attachment of ACC3 cells, or that ACC3 cells trap and retain ACC‐FN in their pericellular space. This isoform of FN may play an important role in the mode of invasion of ACC and the formation of stromal pseudocysts in the characteristic cribriform structure of ACC.