Assessment of the function of the C-subunit of activin in cultured hepatocytes

Wada, Wataru, Akito Maeshima, You-Qing Zhang, Yoshihisa Hasegawa, Hiroyuki Kuwano, and Itaru Kojima. Assessment of the function of the C-subunit of activin in cultured hepatocytes. Am J Physiol Endocrinol Metab 287: E247–E254, 2004. First published March 23, 2004; 10.1152/ajpendo.00390.2003.—We assessed the function of the C-subunit of activin in hepatocytes. We studied the effect of conditioned medium of Chinese hamster ovary (CHO) cell line stably expressing the C gene (CHOC) on growth of AML12 hepatocytes. We also examined the effect of recombinant activin C and transfection of the C gene by using adenovirus vector. CHOC secreted activin C, a homodimer of the C, as well as precursors of the C. The conditioned medium of CHOC increased both [H]thymidine incorporation and the cell number in AML12 cells. It also supported survival of AML12 cells in a serum-free condition. Recombinant human activin C also increased both [H]thymidine incorporation and the number of AML12 cells. Transfection of AML12 cells with the C-subunit led to the stimulation of [H]thymidine incorporation. Analysis of the conditioned medium revealed that the Csubunit formed a heterodimer with the endogenous A, the formation of which was dependent on the amount of C expressed. Recombinant activin C did not affect the binding of I-activin A to its receptor or follistatin. These results indicate that activin C stimulates growth of AML12 cells. The C-subunit modifies the function of the A-subunit by multiple mechanisms.