Growth hormone expression in human Burkitt lymphoma serum-free Ramos cell line

A human nonpituitary cell line grown under serum-free (sf) conditions (sfRamos Burkitt lymphoma cell line) has been reported to secrete a 29K PRL-like peptide which acts as an autocrine growth factor. Conditioned medium from these cells was examined for lactogenic activity using the Nb2 bioassay and RIAs specific for human GH (hGH) and hPRL. SfRamos conditioned medium stimulated the growth of Nb2 cells. Anti-hGH monoclonal antibodies but not anti-hPRL inhibited the mitogenic effect of sfRamos conditioned medium on Nb2 cells. Immunoreactive hGH but not hPRL was detected by RIA. Immunoprecipitation with anti-hGH polyclonal antibody followed by Western blot analysis with anti-hGH monoclonal antibody revealed a specific 22K band with the same mobility as pituitary hGH. Northern blot analysis with an hGH complementary DNA (cDNA) probe revealed a 1.0-kilobase transcript migrating coincident with pituitary hGH messenger RNA. A less abundant, 1.6-kilobase transcript was also observed. Reverse transcriptase-polymerase chain reaction using specific primers for the hGH cDNA generated the predicted 248-base pair band. Polymerase chain reaction sequencing of this fragment revealed sequence identity to the hGH-N cDNA, demonstrating conclusively the expression of the hGH-N gene in the sfRamos cell line.