title: Growth hormone acts on the synthesis and secretion of alpha-casein in bovine mammary epithelial cells.
abstract: To study the effect of growth hormone (GH) on the functions of mammary epithelia, we examined the effect of GH on the synthesis and secretion of alpha-casein in a bovine mammary epithelial cell (BMEC) clonal line, which was established from a 26-d-pregnant Holstein heifer. GH receptors (GHR) were observed in the BMEC on the membrane as well as in the cytoplasm. After BMEC were plated onto cell culture inserts, GH stimulated alpha-casein release in both the presence and absence of the lactogenic hormone complex, which included dexamethasone, insulin and prolactin (DIP). DIP enhanced the effect of GH on alpha-casein release. Although alpha(s1-) casein mRNA expression was not detected in untreated control cells, its expression was observed in BMEC in response to the GH, DIP and GH + DIP treatments. Expression was greater for GH and GH + DIP than for just DIP. Expression of GHR mRNA was increased by DIP treatment, while the mRNA expression was little changed by GH treatment. We conclude that GH acts on BMEC and induces the expression of both the alpha-casein gene and protein. GHR gene expression was shown to be regulated by DIP and GHR. GHR may be involved in a synergic effect between GH and DIP on casein secretion. These results suggest that GH, in addition to its widely accepted homeorhetic role in vivo, also can act on the mammary parenchyma, and that the effects of GH on mammary epithelial cells could partly account for the clear galactopoietic effect of recombinant bovine GH seen in lactating dairy cows.
authors.affiliation: Laboratory of Animal Physiology, Graduate School of Agriculture, Tohoku University, Aoba-ku, Sendai 981-8555, Japan. yobara@bios.tohoku.ac.uk
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Tokushi
authors.initials: T
authors.lastname: Komatsu
authors.forename: Takuya
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Michael T
authors.initials: MT
authors.lastname: Rose
authors.forename: Hisashi
authors.initials: H
authors.lastname: Aso
authors.forename: Akihiko
authors.initials: A
authors.lastname: Hagino
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Obara
mesh_terms: D000818:Animals; D002364:Caseins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D002417:Cattle / Q000502:physiology*; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D004847:Epithelial Cells / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D013006:Growth Hormone / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology; D007774:Lactation; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D011388:Prolactin / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D011986:Receptors, Somatotropin / Q000032:analysis / Q000235:genetics; D011994:Recombinant Proteins / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D002364:Caseins; D007328:Insulin; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D011994:Recombinant Proteins; D003907:Dexamethasone; D011388:Prolactin; D013006:Growth Hormone