Cloning and nucleotide sequencing of rat lymphocyte growth hormone cDNA

The messenger RNA for rat growth hormone (GH) was isolated from rat spleen lymphocytes and cloned as a cDNA after PCR. Four clones, including part of the prehormone sequence and the full-length mature GH sequence, were obtained and sequenced. The sequence data revealed that rat lymphocyte GH was identical to that reported for pituitary GH. The results do not support the expression by alternate splicing of the 20-kD variant described in the pituitary. We also cloned the promoter of lymphocyte GH and analyzed its nucleotide sequence including 300 base pairs of the 5'-flanking region. The promoter sequence we obtained did not exactly match that reported in the literature because of reading compressions on the gel. However, parellel sequencing of thymus, spleen and pituitary GH promoter sequences gave identical patterns of compressions in the gel. The results suggest that the sequence in all the tissues was the same. Collectively, these studies demonstrate that lymphocytes express authentic GH mRNA and suggest that GH gene expression may be regulated in immune tissue by similar transcriptional factors to those described in the pituitary.