Induction in the expression of an unusual proline-rich protein by pig tracheal surface epithelial cells maintained in primary culture

Primary cell culture is a valuable tool for studying the regulation of gene expression since many differentiated traits are conserved. Cells cultured from the epithelial lining of pig trachea were selected as a model system for mucin synthesis. RNAs were isolated from pig trachea epithelial linings and from pig trachea surface epithelial cells cultured in serum-free media. Cell free translations showed an unusually high incorporation of [³H]proline into a relatively small protein (about 20 kDa), but only with RNA from the cells in culture. RNA prepared from pig trachea cells immediately before placing the cells in culture (day 0) did not contain mRNA encoding this unusual proline-rich protein. However, the expression of this protein was dramatically induced within 2 days of maintaining the cells in culture.