ESPE Abstracts

Background: GH transduction defect (GHTD) is characterised by severe short stature and impaired STAT3 phosphorylation, which is overcome by simultaneous induction of GHTD fibroblasts with 200 ng/ml GH and short interference mRNA CIS (GH200/siRNA) or with 1 000 ng/ml GH (GH1000) and is clinically expressed with ‘catch-up’ growth after rhGH treatment.

Objective and hypotheses: The involvement of epidermal growth factor receptor (EGFR) in the successful GH signaling and the role of p21 in the regulation of the GH/GHR and EGF/EGFR pathways were studied in one control and one GHTD patient.

Method: Fibroblast cultures were developed from gingival biopsies of one GHTD patient (PF) and one control (CF).The protein expression and cellular localization of EGFR, pEGFR and p21 were studied by Western Immunoblotting and Immunofluorescence respectively, i)At the basal state and after induction with GH200,either with or without siRNA CIS and ii)At the basal state and after inductions with GH200,GH1000 or 50 ng/ml EGF.

Results: After GH200/siCIS: i) The protein expression and the membrane localisation of EGFR and pEGFR were increased, especially in PF, ii) The protein expression and the nuclear localisation of p21 was reduced in CF and PF. In the inductions of successful GH signalling (GH200 in CF and GH1000 in PF): i) The protein expression and the membrane localization of EGFR and pEGFR were increased, ii) The protein expression and nuclear localization of p21 were reduced. After induction with EGF: i) The protein and membrane expression of EGFR and pEGFR were increased similarly in CF and PF, ii) The protein expression of p21 was increased in CF and PF.

Conclusion: The EGFR participates in the successful GH signalling, but induction with a higher dose of hGH is needed in the PF. The EGF/EGFR pathway, which is more primed in P than in C, is possibly involved when exogenous rhGH is administered. Also, p21 is a negative regulator of the EGF/EGFR pathway, which unlike the GH/GHR pathway, is not impaired in the PF.