Synthesis and secretion of alpha-fetoprotein and albumin by newborn rat brain cells in culture

Brain cells of newborn rat were found to synthesize and secrete alpha-fetoprotein (AFP) and albumin in short-term culture. Synthesis of AFP and albumin was demonstrated by time-related linear incorporation of [¹⁴C]leucine into immunoprecipitable AFP and albumin by brain cells from newborn rat during 6 h incubation of the cultures. Newly synthesized labeled AFP and albumin were also accumulated (secreted) linearly as a function of incubation period. Cycloheximide could inhibit this incorporation of [¹⁴C]leucine into immunoprecipitable AFP and albumin. Synthesis of AFP and albumin accounted for 11-13% and 5-6% respectively, while their secretion into the culture medium was about 27-30% and 11-13% respectively of the total proteins synthesized and secreted by brain cells of newborn rat. Rate of AFP synthesis was about 2-fold greater than that of albumin. AFP and albumin secreted by brain cells displayed a complete immunological identity with, and electrophoretic mobilities similar to, the serum AFP and albumin. Molecular weights of AFP and albumin secreted by brain cells were also similar to their corresponding serum proteins. AFP was identified as the only active estradiol binding protein secreted by newborn rat brain cells in culture. Our studies suggest that albumin and estrophilic AFP originate in the developing rat brain in situ by intracellular synthesis.