Hydrocortisone stimulation of DNA synthesis in bromodeoxyuridine-selected non-dividing WI-38 cells

Ostensibly noncycling WI-38 cells were selected by incubating growing cultures for 7 days with 10(-5) M bromodeoxyuridine. These cells were then exposed to Hoechst dye 33258, and then visible light which kills cells that incorporated bromodeoxyuridine. Following selection, cultures were refed with medium containing 10% fetal bovine serum. By autoradiography, we determined that less than 10% of these cells could incorporate [3H]thymidine during the next 7 days. This value was increased to 25% or more by adding hydrocortisone to the medium. The proliferative response was also increased by refeeding cultures with hydrocortisone-containing medium conditioned 24 h by freshly seeded mid-, but not late, population doubling level (PDL) cultures. Medium conditioned without hydrocortisone did not stimulate incorporation of [3H]thymidine beyond the control value. These results show that: (1) cells that might otherwise not initiate DNA synthesis are stimulated to do so by hydrocortisone; (2) hydrocortisone-conditioned medium from mid-PDL culture increases this stimulation; and (3) hydrocortisone-conditioned medium from late PDL cultures is not stimulatory.