SYNTHESIS OF FIBRONECTIN AND LAMININ BY TYPE-II PULMONARY EPITHELIAL-CELLS

Previous investigations demonstrated that type II pulmonary epithelial cells regulate extracellular matrix deposition as a function of time in primary culture. In those studies, the matrix fraction was analyzed as a whole. The present work focused on two components of the type II cell matrix, fibronectin and laminin. These glycoproteins have differ ing effects on differentiation of type II cells in primary culture. Fi bronectin synthesis was quantitated between day I and day 6 in the cel ls, matrix, and medium; laminin synthesis was quantitated only in the cells. Although total fibronectin synthesis was regulated as a functio n of time in culture, reaching its greatest value on day 2, the averag e proportion of newly synthesized fibronectin in the cells (35%), medi um (50%), and matrix (15%) remained constant over a B-day interval. Be tween day 2 and day 6, the relative abundance of fibronectin messenger RNA increased 6.5-fold. Rates of cellular laminin synthesis did not v ary with time in culture. These results support a role for differentia l regulation of fibronectin and laminin synthesis to determine the com position of the type II cell extracellular matrix.