Synthesis of laminin and entactin by F9 cells induced with retinoic acid and dibutyryl cyclic AMP.

Mouse embryonal carcinoma F9 cells were exposed to retinoic acid and dibutyryl cyclic AMP. The treated cells synthesized and secreted into the culture medium the basal lamina components, laminin (GP-1 and GP-2) and entactin. The time course of secretion of the basal lamina components was examined by electron microscopic and immunochemical procedures. The induction of the cells resulted in major morphological changes and the deposition of both laminin and entactin at the cell surface and cell junctions. Intracellular deposits of laminin could be localized to the endoplasmic reticulum and membrane-bound intracytoplasmic vacuoles. Concomitant with the appearance of laminin and entactin, there was a loss of fibronectin synthesis and a marked decrease in a 190,000-Da sulfated glycoprotein that appeared to be related to entactin. In the induced cells, laminin and entactin were associated in a complex that could be dissociated with low concentrations of sodium dodecyl sulfate. The induction of laminin and entactin seem to be independent. The enhanced synthesis of laminin appeared to be under transcriptional regulation since it was found that induced F9 cells contained translatable mRNA for GP-2 when tested in a rabbit reticulocyte lysate system. The uninduced cells did not contain detectable quantities of translatable GP-2 mRNA.