Endocrinology, Vol 136, 1258-1266, Copyright © 1995 by Endocrine Society

ARTICLES

N-terminal-truncated recombinant analogs of bovine placental lactogen: interaction with human and rat growth hormone receptors and insulin- like growth factor-I secretion mediated by somatogenic receptors in rat hepatocytes

D Vashdi-Elberg, NR Staten, E Sakal, GG Krivi and A Gertler
Department of Biochemistry, Food Science, and Nutrition, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel.

Bovine placental lactogen (bPL) was found to be as potent as human GH (hGH) in its ability to bind to soluble full-size recombinant hGH- binding protein (hGHBP) and to membrane-embedded hGH receptor in intact IM-9 human lymphocytes. bPL was also capable of forming a 1:2 complex with hGHBP, although the structure of this complex was probably more compact than that with hGH. Removal of 13 amino acids from the N- terminus of bPL did not affect its ability to bind to hGHBP or hGH receptors in intact IM-9 cells. Its ability to form a 1:2 complex with hGHBP was, however, impaired, unlike that of a corresponding analog in which an L28F mutation has been simultaneously introduced. Truncation of 17 amino acids decreased its affinity toward both hGHBP and GH receptors on intact IM-9 lymphocytes and in liver rat microsomal fraction and inhibited the formation of 1:2 complexes with hGHBP. Simultaneous L28F mutation did not affect affinity toward hGHBP, but increased affinity toward rat liver GH receptors and restored affinity toward membrane-embedded hGH receptors in IM-9 lymphocytes and the ability to form a 1:2 complex with hGHBP. Truncation of 20 amino acids further decreased affinity toward both hGHBP and receptors in intact IM- 9 lymphocytes and completely abolished formation of a 1:2 complex with hGHBP. Both des-13-bPLs and bPL-des-17 (L28F) retained their full ability to stimulate insulin-like growth factor-I secretion by rat hepatocytes compared to that of bPL. The insulin-like growth factor-I stimulatory activities of bPL-des-17 and bPL-des-20, however, were decreased to 1-5%. These results indicate that the stoichiometry of 1:2 complex formation with hGHBP may be preserved despite decreased receptor binding affinity, but the lower affinity of the putative site 1 or site 2 of the analog may account for the decrease in biological activity. Furthermore, the ability or inability of bPL or its truncated analogs to form 1:2 complexes with soluble hGHBP cannot predict their somatogen receptor-mediated biological activity in rat hepatocytes.

This article has been cited by other articles:

				E. Biener, C. Martin, N. Daniel, S. J. Frank, V. E. Centonze, B. Herman, J. Djiane, and A. Gertler Ovine Placental Lactogen-Induced Heterodimerization of Ovine Growth Hormone and Prolactin Receptors in Living Cells Is Demonstrated by Fluorescence Resonance Energy Transfer Microscopy and Leads to Prolonged Phosphorylation of Signal Transducer and Activator of Transcription (STAT)1 and STAT3 Endocrinology, August 1, 2003; 144(8): 3532 - 3540. [Abstract] [Full Text] [PDF]

				A. Herman, C. Bignon, N. Daniel, J. Grosclaude, A. Gertler, and J. Djiane Functional Heterodimerization of Prolactin and Growth Hormone Receptors by Ovine Placental Lactogen J. Biol. Chem., February 25, 2000; 275(9): 6295 - 6301. [Abstract] [Full Text] [PDF]

				A. Herman, D. Helman, O. Livnah, and A. Gertler Ruminant Placental Lactogens Act as Antagonists to Homologous Growth Hormone Receptors and as Agonists to Human or Rabbit Growth Hormone Receptors J. Biol. Chem., March 19, 1999; 274(12): 7631 - 7639. [Abstract] [Full Text] [PDF]

				E Juarez-Aguilar, F Castro-Munozledo, N. Guerra-Rodriguez, D Resendez-Perez, H. Martinez-Rodriguez, H. Barrera-Saldana, and W Kuri-Harcuch Functional domains of human growth hormone necessary for the adipogenic activity of hGH/hPL chimeric molecules J. Cell Sci., January 9, 1999; 112(18): 3127 - 3135. [Abstract] [PDF]

				D. Helman, N. R. Staten, J. Byatt, J. Grosclaude, R. E. McKinnie, J. Djiane, and A. Gertler Site-Directed Mutagenesis of Recombinant Bovine Placental Lactogen at Lysine-73 Leads to Selective Attenuation of Its Somatogenic Activity Endocrinology, October 1, 1997; 138(10): 4069 - 4080. [Abstract] [Full Text] [PDF]

				D. Vashdi-Elberg, N. R. Staten, E. Sakal, R. E. McKinnie, J. Djiane, G. G. Krivi, and A. Gertler Selective Modification of Recombinant Bovine Placental Lactogen by Site-directed Mutagenesis at Its C Terminus J. Biol. Chem., March 8, 1996; 271(10): 5558 - 5564. [Abstract] [Full Text] [PDF]