AJP - Cell Physiology, Vol 255, Issue 3 C261-C270, Copyright © 1988 by American Physiological Society
Growth-dependent regulation of system A in SV40-transformed fetal rat hepatocytes
M. E. Handlogten and M. S. Kilberg
Department of Biochemistry and Molecular Biology, University of Florida School of Medicine, Gainesville 32610.
Fetal RLA209-15 hepatocytes, transformed with a temperature-sensitive SV40
mutant, behave like fully differentiated cells at the growth-restrictive
temperature of 40 degrees C. Conversely, incubation at the
growth-permissive temperature of 33 degrees C results in a transformed
phenotype characterized by rapid cell division and decreased production of
liver-specific proteins. The results presented here demonstrate that the
cells at 33 degrees C exhibited high rates of system A transport, but
transfer to 40 degrees C reduced the activity greater than 50% within 24 h.
This decline in transport was independent of cell density, although the
basal rate of uptake was inversely proportional to cell density in rapidly
dividing cells. Transfer of cells from 40 to 33 degrees C resulted in an
enhancement of system A activity that was blocked by tunicamycin. Plasma
membrane vesicles from cells maintained at either 33 or 40 degrees C
retained uptake rates proportional to those in the intact cells; this
difference in transport activity could also be demonstrated after detergent
solubilization and reconstitution. Collectively, these data indicate that
de novo synthesis of the system A carrier is regulated in conjunction with
temperature-dependent cell growth in RLA209-15 hepatocytes.
