A proteinous factor mediating intercellular communication during the transition of Dictyostelium cells from growth to differentiation.

In general, cell differentiation and proliferation are mutually exclusive. Transition of the cellular slime mold Dictyostelium discoideum from growth to differentiation is triggered mainly by a secreted factor(s) in addition to nutritional deprivation. To purify and identify the factor required for the growth/differentiation transition, a new assay system was designed. Under low-nutrient conditions, cells could grow to multiply, but never developed. The cellular development including aggregation, however, was induced by the addition of conditioned medium (CM) in which growing or starving Dictyostelium cells had been cultured. The CM inhibited the synthesis of nuclear DNA and induced the cells to acquire chemotactic competence to cAMP, thus suggesting the presence of a secreted factor(s) required for growth/differentiation transition in the CM. The active factor(s) in CM (referred to as CMF450; conditioned medium factor) was found to be sensitive to heat and have a large molecular size. The CMF450 was purified using FPLC through a gel filtration column, and was identified to be a proteinous macromolecule of Mr 450 kDa, which was mainly composed of 94 kDa, 79 kDa, and 49 kDa subunits under a native condition.