Cellular activities of 20K- and 22K-hGH do not necessarily correlate with their binding affinities for rat GH receptor.
Even though 20K human growth hormone (20K-hGH) has 3-10% binding affinity for the rat liver and adipose tissue microsomes as compared to 22K-hGH, it was also reported that 20K-hGH has the same potency as 22K-hGH in the hypophysectomized rat weight gain assay. In order to investigate the reason why such controversial data exist, we have studied 20K- and 22K-hGH using the rat GH receptor extracellular domain (rGHR-ECD) and full-length rGHR. When we examined the complex formation of rGHR-ECD with 20K- and 22K-hGH in gel filtration assay, 20K-hGH formed no complex while 22K-hGH formed a 1:1 complex. Next, rGHR cDNA was introduced into Ba/F3 cells and CHO-K1 cells, and stable transfectants (Ba/F3-rGHR and CHO-rGHR) were established. In the proliferation of Ba/F3-rGHR cells, 20K-hGH had 10-fold lower activity than 22K-hGH, which is consistent with their affinities for rGHR. But surprisingly, in the Spi2.1 gene promoter activation in CHO-rGHR cells, 20K- and 22K-hGH had the same activity, which was found not only in stable CHO-rGHR clones but also in CHO-K1 cells transiently expressing rGHR. In conclusion, these results indicate that cellular activities of 20K- and 22K-hGH do not necessarily correlate with their binding affinities for rGHR.
Ikeda
M
M
Pharmaceuticals Section, Life Science Laboratories, Mitsui Chemicals, Inc., Mobara, Chiba, Japan.
Matsumoto
K
K
Uchida
H
H
Naito
N
N
Tsunekawa
B
B
Wada
M
M
Honjo
M
M
D000273:Adipose Tissue / Q000648:ultrastructure; D000818:Animals; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002850:Chromatography, Gel; D006224:Cricetinae; D015870:Gene Expression; D019382:Human Growth Hormone / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007016:Hypophysectomy; D008861:Microsomes / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000235:genetics; D010446:Peptide Fragments / Q000737:chemistry; D011401:Promoter Regions, Genetic; D051381:Rats; D011986:Receptors, Somatotropin / Q000378:metabolism; D013329:Structure-Activity Relationship; D014162:Transfection
C091103:LOC299282 protein, rat; D009687:Nuclear Proteins; D010446:Peptide Fragments; D011986:Receptors, Somatotropin; D019382:Human Growth Hormone