Change in phenotype in long-term cultures of a clonal rat bone cell line: switch to the synthesis of alpha 1(I)-trimer collagen.

Abstract

A number of bone cell clones isolated from rat calvaria have been maintained in culture for more than 3 years. Several of these clones have undergone dramatic changes in phenotype. One of these clones, RCB 2.2, was observed originally to have a fibroblastic morphology in culture and to respond to parathyroid hormone (PTH), but not prostaglandin E2 (PGE2), with an increase in intracellular cAMP. Throughout several passages in early subcultures, these cells synthesized mostly type I collagen, with small amounts of type III and type V collagens. Whereas PTH had no detectable effect on collagen synthesis, PGE2 decreased the amount of total cell layer collagen, with the greatest effect on type III collagen, while increasing the proportion of type V collagen. Subsequent studies on these cells during 3 years in culture have indicated changes in their phenotype including a progressive change in morphology to a more cuboidal shape and a change in collagen synthesis, the cells producing large amounts of the "embryonic" collagen, alpha 1(I) trimer. The reason(s) for the change in collagen expression is unknown, but may be the result of a change in which gene(s) is being expressed.