INVERSE EFFECTS OF 20K AND 22K HUMAN GROWTH-HORMONES ON THE GROWTH OFT-47D HUMAN BREAST-CANCER CELLS IN CULTURE AND IN NUDE-MICE

The major form of human growth hormone (22K hGH) stimulates the growth of T-47D human breast cancer cells in culture and in nude mice by bin ding to their receptors for growth hormone and prolactin. Another isof orm of hGH having a smaller molecular mass (20K hGH) is known to show different binding affinities to these receptors. In this study, we hav e analyzed the effects of 20K hGH on the growth of T-47D cells in vitr o and in vivo. 20K hGH (50 ng/ml) inhibited the proliferation and DNA synthesis of T-47D cells cultured in the presence and absence of 17 be ta-estradiol (100 ng/ml), while 22K hGH (50 ngl mi) promoted the cellu lar growth. In estradiol-treated nude mice, 22K hGH (100 mu g) remarka bly promoted the growth of T-47D tumor, but 20K hGH again suppressed t he tumor growth significantly. The results suggest the presence of dif ferent signal pathways for these two hGH isoforms and imply a possible clinical application for 20K hGH.