The 20-kilodalton (kDa) human growth hormone (hGH) differs from the 22-kDa hGH in the effect on the human prolactin receptor.
Previously we have demonstrated that 20-kDa human GH (20K-hGH) is a full agonist for hGH receptor (hGHR) even though its complex formation with hGHR and hGH-binding protein differs from that of 22-kDa human GH (22K-hGH). In this study, we focused on the effect of 20K-hGH on human PRL receptor (hPRLR). To elucidate the effects of 20K-hGH on hPRLR and compare them with those of 22K-hGH, we prepared two cells stably expressing full-length hPRLR, Ba/F3-hPRLR and CHO-hPRLR. In the proliferation of Ba/F3-hPRLR cells, which can grow in a dose-response to lactogenic hormones, both 20K- and 22K-hGH exhibited bell-shaped curves in the absence of exogenous zinc ion (Zn2+); however, the curve of 20K-hGH was shifted to a 10-fold higher concentration than that of 22K-hGH in view of EC50 value (the EC50 of 20K- and 22K-hGH were 15 nM and 1.5 nM, respectively). Addition of Zn2+ up to 25 microM increased the activities of both 20K- and 22K-hGH; however, the enhancement by Zn2+ was greater in 20K-hGH than in 22K-hGH, thereby the activities of both hGH isoforms reached the same level at 25 microM Zn2+. Nevertheless, in the presence of 0.25-1 microM free Zn2+, which is equal in human serum, the activity of 20K-hGH was still lower than that of 22K-hGH. The modest effect of 20K-hGH on activating hPRLR in the absence of Zn2+ was confirmed in the rat serine protease inhibitor 2.1 (Spi2.1) gene promoter activation and JAK2/Stat5 tyrosine phosphorylation in CHO-hPRLR. In addition, in human breast cancer cell T-47D, 20K-hGH was proved to stimulate Stat5 tyrosine phosphorylation to much lower degree than 22K-hGH via not hGHR but hPRLR. Taken together, our data suggest that 20K-hGH may be a weaker agonist for hPRLR than 22K-hGH in the human body; therefore 20K-hGH may alleviate the hPRLR-mediated side-effects such as breast cancer when administered to human body.
Tsunekawa
B
B
Life Sciences Laboratory, Performance Materials R&D Center, Mitsui Chemicals, Inc., Chiba, Japan.
Wada
M
M
Ikeda
M
M
Uchida
H
H
Naito
N
N
Honjo
M
M
D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism; D019382:Human Growth Hormone / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D006801:Humans; D053614:Janus Kinase 2; D051379:Mice; D008894:Milk Proteins; D008970:Molecular Weight; D009154:Mutation / Q000502:physiology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D011981:Receptors, Prolactin / Q000187:drug effects*; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
D004268:DNA-Binding Proteins; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D011981:Receptors, Prolactin; D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D019382:Human Growth Hormone; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; C507927:Jak2 protein, rat; D053614:Janus Kinase 2; D015032:Zinc