Insulin-like growth factor as a novel stimulator for somatolactin secretion and synthesis in carp pituitary cells via activation of MAPK cascades

Am J Physiol Endocrinol Metab. 2011 Dec;301(6):E1208-19. doi: 10.1152/ajpendo.00347.2011. Epub 2011 Aug 23.

Abstract

Somatolactin (SL), a member of the growth hormone/prolactin family, is a pituitary hormone unique to fish models. Although SL is known to have diverse functions in fish, the mechanisms regulating its secretion and synthesis have not been fully characterized. Using grass carp pituitary cells as a model, here we examined the role of insulin-like growth factor (IGF) in SL regulation at the pituitary level. As a first step, the antisera for the two SL isoforms expressed in the carp pituitary, SLα and SLβ, were produced, and their specificity was confirmed by antiserum preabsorption and immunohistochemical staining in the carp pituitary. Western blot using these antisera revealed that grass carp SLα and SLβ could be N-linked glycosylated and their basal secretion and cell content in carp pituitary cells could be elevated by IGF-I and -II treatment. These stimulatory effects occurred with parallel rises in SLα and SLβ mRNA levels, and these SL gene expression responses were not mimicked by insulin but blocked by IGF-I receptor inactivation. In carp pituitary cells, IGF-I and -II could induce rapid phosphorylation of IGF-I receptor, MEK1/2, ERK1/2, MKK3/6, and p38 MAPK; and SLα and SLβ secretion, protein production, and mRNA expression caused by IGF-I and -II stimulation were negated by inactivating MEK1/2 and p38 MAPK. Parallel inhibition of PI3K and Akt, however, were not effective in these regards. These results, taken together, provide evidence that IGF can upregulate SL secretion and synthesis at the pituitary level via stimulation of MAPK- but not PI3K/Akt-dependent pathways.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carps* / metabolism
  • Enzyme Activation / drug effects
  • Enzyme Activation / physiology
  • Female
  • Fish Proteins / biosynthesis*
  • Fish Proteins / genetics
  • Fish Proteins / metabolism*
  • Gene Expression Regulation / drug effects
  • Glycoproteins / biosynthesis*
  • Glycoproteins / genetics
  • Glycoproteins / metabolism*
  • Immunohistochemistry
  • Insulin-Like Growth Factor I / pharmacology*
  • Insulin-Like Growth Factor I / physiology
  • MAP Kinase Signaling System / drug effects*
  • MAP Kinase Signaling System / physiology
  • Male
  • Pituitary Gland / cytology
  • Pituitary Gland / drug effects*
  • Pituitary Gland / metabolism
  • Pituitary Hormones / biosynthesis*
  • Pituitary Hormones / genetics
  • Pituitary Hormones / metabolism*
  • Protein Kinase Inhibitors / pharmacology
  • Signal Transduction / drug effects
  • Signal Transduction / physiology
  • Stimulation, Chemical
  • Up-Regulation / drug effects

Substances

  • Fish Proteins
  • Glycoproteins
  • Pituitary Hormones
  • Protein Kinase Inhibitors
  • somatolactin protein, fish
  • Insulin-Like Growth Factor I