The purpose of this project is to characterize the components involved in signalling through interferon (ifn) and cytokine receptors. Several cytokines as well as ifns alpha and gamma regulate gene expression by the tyrosine phosphorylation of a family of DNA binding factors which have the 91 kDa (p91 or Stat1) protein of ISGF3 as a common component. These activated protein complexes bind to enhancers present in the promoters of early response genes such as the high affinity Fcgamma receptor (FcgammaR1). Our studies have shown that the activation of p91 or other closely related members of this protein family occurs through the receptors for several cytokines and growth factors. Treatment of human peripheral blood monocytes or basophils with interleukin-3 (IL-3), interleukin-5 (IL-5), interleukin-10 (IL-10), granulocyte-macrophage colony stimulating factor , growth hormone, prolactin or the ifns differentially activated DNA-binding proteins all of which recognized the same IFN gamma response region (GRR) located in the promoter of the FcgammaRI gene. Further studies using murine cell lines that are stably transfected with full length or mutated growth hormone or prolactin receptors have helped identify sequences in the cytoplasmic tail of the receptor that are required for the activation and also the deactivation of the GRR binding complex. Currently, immunological studies with these cell lines and antibodies to various putative components of the growth hormone signalling cascade are being used to delineate the sequence of events and protein associations that occur during growth hormone signalling. These studies are providing a broader understanding of the components involved in signalling through cytokine receptors and consequently the mechanisms of cytokine stimulated gene activation.
