Modulation of calmodulin gene expression as a novel mechanism for growth hormone feedback control by insulin-like growth factor in grass carp pituitary cells.
Calmodulin (CaM), the Ca2+ sensor in living cells, is essential for biological functions mediated by Ca2+-dependent mechanisms. However, modulation of CaM gene expression at the pituitary level as a means to regulate pituitary hormone synthesis has not been characterized. In this study we examined the functional role of CaM in the feedback control of GH by IGF using grass carp pituitary cells as a cell model. To establish the structural identity of CaM expressed in the grass carp, a CaM cDNA, CaM-L, was isolated from the carp pituitary using 3'/5' rapid amplification of cDNA ends. The open reading frame of this cDNA encodes a 149-amino acid protein sharing the same primary structure with CaMs reported in mammals, birds, and amphibians. This CaM cDNA is phylogenetically related to the CaM I gene family, and its transcripts are ubiquitously expressed in the grass carp. In carp pituitary cells, IGF-I and IGF-II induced CaM mRNA expression with a concurrent drop in GH transcript levels. These stimulatory effects on CaM mRNA levels were not mimicked by insulin and appeared to be a direct consequence of IGF activation of CaM gene transcription without altering CaM transcript stability. CaM antagonism and inactivation of calcineurin blocked the inhibitory effects of IGF-I and IGF-II on GH gene expression, and CaM overexpression also suppressed the 5' promoter activity of the grass carp GH gene. These results, as a whole, provide evidence for the first time that IGF feedback on GH gene expression is mediated by activation of CaM gene expression at the pituitary level.
Huo
Longfei
L
Department of Zoology, University of Hong Kong, Room 4S-12, Kadoorie Biological Sciences Building, Pokfulam Road, Hong Kong, SAR, Peoples Republic of China.
Fu
Guodong
G
Wang
Xinyan
X
Ko
Wendy K W
WK
Wong
Anderson O L
AO
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002147:Calmodulin / Q000235:genetics*; D002347:Carps / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D025461:Feedback, Physiological / Q000235:genetics*; D015870:Gene Expression / Q000502:physiology; D013006:Growth Hormone / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000166:cytology / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis
D002147:Calmodulin; D018076:DNA, Complementary; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone