Replacement of serum in cell culture by hormones: A study of hormonal regulation of cell growth and specific gene expression

Abstract

The hypothesis that the growth of mammalian cells is regulated by hormones is now supported by considerable evidence. Two rat pituitary cell lines, GH ₃ and GC, a mouse melanoma, M2R (B16), and a human cervical carcinoma cell, HeLa S‐3, have been grown indefinitely in serum‐free (SF) hormone‐supplemented medium. No visible changes of growth characteristics were observed in the cells grown continuously in the SF condition. However, changes in the activity of a plasma membrane enzyme, alkaline phosphatase, and in the relative intensity of surface proteins that are labeled by the [ ¹²⁵ l] lactoperoxidase technique were found in HeLa cells grown in the SF condition.

To study the role of hormones required in the regulation of cell growth, HeLa cells were grown in the absence of one of the required hormones. The following results were obtained. Epidermal growth factor is probably involved in the regulation of the synthesis of macromolecules such as RNA and of the protein content per cell. Transferrin, the accessory factor in the SF condition, supplies iron for cells. The two basic peptides in this SF system, fibroblast growth factor and insulin, are probably involved in the balance of nutrients and energy inside the cell. The replacement of F12 medium with a better‐balanced medium, MCDB 105, can mimic the requirements for these two peptides. The steroid hydrocortisone (HC) is probably involved in alteration of the cell surface. This is indicated by the effects of HC on cell morphology, rate of detachment from the dish, and the pattern of [ ¹²⁵ l] lactoperoxidase labeling of surface proteins. In addition, it is necessary to change the medium more frequently to maintain the culture in the medium without HC. This observation suggests that HC may be involved in the control of homeostatic properties of the cell surface.

The production of rat prolactin by GH ₃ cells was also studied. GH ₃ cells in the SF condition produce 1.6 μg prolactin per 70 ^s cells in 24 h, while 2.4 μg is produced in the presence of serum. Prolactin production in the SF condition is enhanced by the presence of thyrotropin‐releasing hormone and inhibited by triiodothyronine (T ₃ ). T ₃ ^AS the major growth factor for these cells. Without it cell growth is severely limited, while prolactin production is elevated. This result suggests that the GH ₃ cell line in the SF condition may be an ideal system for the study of hormonal regulation of cell growth and specific gene expression.