A RETINOIC ACID-INDUCED CLONAL CELL-LINE DERIVED FROM MULTIPOTENTIAL P19 EMBRYONAL CARCINOMA-CELLS EXPRESSES SMOOTH-MUSCLE CHARACTERISTICS

Despite intense interest in understanding the differentiation of vascu lar smooth muscle, very little is known about the cellular and molecul ar mechanisms that control differentiation of this cell type. Progress in this field has been hampered by the lack of an inducible in vitro system for study of the early steps of smooth muscle differentiation. In this study, we describe a model system in which multipotential mous e P19 embryonal carcinoma cells (P19s) can be induced to express multi ple characteristics of differentiated smooth muscle. Treatment of P19s with retinoic acid was associated with profound changes in cell morph ology and with the appearance at high frequency of smooth muscle alpha -actin-positive cells that were absent or present at extremely low fre quency in parental P19s. A clonal line derived from retinoic acid-trea ted P19s (9E11G) stably expressed multiple characteristics of differen tiated smooth muscle, including smooth muscle-specific isoforms of alp ha-actin and myosin heavy chain, as well as functional responses to th e contractile agonists phenylephrine, angiotensin II, ATP, bradykinin, histamine, platelet-derived growth factor (PDGF)-AA, and PDGF-BB. Add itionally, 9E11G cells expressed transcripts for MHox, a muscle homeob ox gene expressed in smooth, cardiac, and skeletal muscles, but not th e skeletal muscle-specific regulatory factors, MyoD and myogenin. Resu lts demonstrate that retinoic acid treatment of multipotential P19 cel ls is associated with formation of cell lines that stably express mult iple properties of differentiated smooth muscle. It remains to be dete rmined whether retinoic acid has induced commitment to a smooth muscle cell lineage as opposed to directly (or indirectly) activating genes characteristic of differentiated smooth muscle cells. However, results suggest that this cell system may be of use in attempting to identify genes involved in controlling smooth muscle differentiation and/or li neage determination.