A novel Y332C missense mutation in the intracellular domain of the human growth hormone receptor does not alter STAT5b signaling: Redundancy of GHR intracellular tyrosines involved in STAT5b signaling

Background: The growth hormone receptor (GHR), upon binding with GH, induces JAK2-mediated phosphorylation of GHR intracellular tyrosines, which then recruit STAT5b. Aberrancies in STAT5b signaling, due to mutations in GHR or STAT5b genes, result in poor responses to GH and severe short stature. Objective: To evaluate and compare the role of a novel Y332C GHR variant identified in a patient with short stature to the other GHR intracellular tyrosines in the GHR-STAT5b signaling process. Results: Recombinant human GHR constructs carrying Y332C or single Y to F changes for each of the 7 intracellular tyrosines did not alter GH-induced GHR-STAT5b signaling in reconstitution studies. However, GH-induced STAT5b activation was specifically abrogated in an hGHR variant in which all 7 tyrosines were inactivated (MYF). When hGHR variants carrying single intracellular tyrosines were evaluated, STAT5b activation was comparable to that of wild-type hGHR only with variants carrying Y534, Y566 or Y627. Conclusion: We provide evidence that in human GHR, 3 intracellular tyrosines are critical and redundant in the GH-induced STAT5b signaling process. This redundancy may explain why an Y332C variant did not alter STAT5b signaling. Identification of missense variants in human GHR intracellular domain should be interpreted with caution and rigorously analyzed.