24-Epibrassinolide at Subnanomolar Concentrations Modulates Growth and Production Characteristics of a Mouse Hybridoma

Brassinosteroids are known to stimulate plant growth and to possess antistress activities in plants. This work was aimed at exploring possible beneficial effects of 24-epibrassinolide on cultured mammalian cells. A mouse hybridoma was cultured either in standard serum-free medium, or in medium diluted to 30%, in which the cells underwent nutritional stress. Steady-state parameters of semicontinuous cultures conducted at 24-epibrassinolide concentrations from 10 - 1 6 to 10 - 9 mol l - 1 were evaluated. Typical effects of the agent found both in standard and in diluted media were (i) increase in the value of mitochondrial membrane potential, (ii), drop of intracellular antibody level, (iii) increase in the fraction of the cells in the G 0 /G 1 phase, and (iv) decrease in the fraction of the cells in the S phase. Alleviation of nutritional stress manifested itself in cultures conducted in diluted media. Viable cell density was significantly higher (relative to control) at 24-epibrassinolide concentrations 10 - 1 3 and 10 - 1 2 mol l - 1 . The results of this exploratory study show that the plant hormone 24-epibrassinolide may induce perturbations in the cell division mechanism, in mitochondria performance, and in secreted protein synthesis in a mammalian cell line. At the lowest brassinosteroid concentrations, the number of steroid molecules in the culture was of the same order of magnitude as the number of viable cells in the culture. This implies involvement of a complex cascade mechanism, through which the steroid molecule induces alterations in gene expression leading finally to significant changes in cell culture parameters.

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