TY - JOUR

T1 - Growth hormone (GH)-independent dimerization of GH receptor by a leucine zipper results in constitutive activation

AU - Behncken, S N

AU - Billestrup, Nils

AU - Brown, R

AU - Amstrup, J

AU - Conway-Campbell, B

AU - Waters, M J

PY - 2000/6/2

Y1 - 2000/6/2

N2 - Growth hormone initiates signaling by inducing homodimerization of two GH receptors. Here, we have sought to determine whether constitutively active receptor can be created in the absence of the extracellular domain by substituting it with high affinity leucine zippers to create dimers of the growth hormone receptor (GHR) signaling domain. The entire extracellular domain of the GHR was replaced by the hemagglutinin-tagged zipper sequence of either the c-Fos or c-Jun transcription factor (termed Fos-GHR and Jun-GHR, respectively). Transient transfection of Fos-GHR or Jun-GHR resulted in activation of the serine protease inhibitor 2.1 promoter in Chinese hamster ovary-K1 cells to a level equal to that achieved by fully activated wild type GHR. Furthermore, stable expression of Jun-GHR alone or Fos-GHR and Jun-GHR together in the interleukin 3-dependent BaF-B03 cell line resulted in cell proliferation after interleukin 3 withdrawal at a rate equal to maximally stimulated wild type GHR-expressing cells. Activation of STAT 5b was also observed in Fos-Jun-GHR-expressing cells at a level equal to that in chronically GH-treated GHR-expressing cells. Thus, forced dimerization of the transmembrane and cytoplasmic domains of the GHR in the absence of the extracellular domain can lead to the constitutive activation of known GH signaling end points, supporting the view that proximity of Janus kinase 2 (JAK2) kinases is the essential element in signaling. Such constitutively active GH receptors may have particular utility for transgenic livestock applications.

AB - Growth hormone initiates signaling by inducing homodimerization of two GH receptors. Here, we have sought to determine whether constitutively active receptor can be created in the absence of the extracellular domain by substituting it with high affinity leucine zippers to create dimers of the growth hormone receptor (GHR) signaling domain. The entire extracellular domain of the GHR was replaced by the hemagglutinin-tagged zipper sequence of either the c-Fos or c-Jun transcription factor (termed Fos-GHR and Jun-GHR, respectively). Transient transfection of Fos-GHR or Jun-GHR resulted in activation of the serine protease inhibitor 2.1 promoter in Chinese hamster ovary-K1 cells to a level equal to that achieved by fully activated wild type GHR. Furthermore, stable expression of Jun-GHR alone or Fos-GHR and Jun-GHR together in the interleukin 3-dependent BaF-B03 cell line resulted in cell proliferation after interleukin 3 withdrawal at a rate equal to maximally stimulated wild type GHR-expressing cells. Activation of STAT 5b was also observed in Fos-Jun-GHR-expressing cells at a level equal to that in chronically GH-treated GHR-expressing cells. Thus, forced dimerization of the transmembrane and cytoplasmic domains of the GHR in the absence of the extracellular domain can lead to the constitutive activation of known GH signaling end points, supporting the view that proximity of Janus kinase 2 (JAK2) kinases is the essential element in signaling. Such constitutively active GH receptors may have particular utility for transgenic livestock applications.

KW - Amino Acid Sequence

KW - Animals

KW - Base Sequence

KW - CHO Cells

KW - Cell Division

KW - Cricetinae

KW - DNA Primers

KW - DNA-Binding Proteins

KW - Dimerization

KW - Growth Hormone

KW - Humans

KW - Leucine Zippers

KW - Milk Proteins

KW - Proto-Oncogene Proteins c-fos

KW - Proto-Oncogene Proteins c-jun

KW - Receptors, Somatotropin

KW - Recombinant Fusion Proteins

KW - STAT5 Transcription Factor

KW - Trans-Activators

M3 - Journal article

C2 - 10828073

VL - 275

SP - 17000

EP - 17007

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

SN - 0021-9258

IS - 22

ER -