Endocrine Abstracts

Introduction. We have reported a family with atypical Laron syndrome with no obvious defect in the growth hormone receptor but with an apparent defect in growth hormone (GH) signaling. We aimed to assess how this signaling defect alters GH-dependent gene expression.

Methods. Atypical Laron fibroblasts (Lfib) and normal fibroblasts (Nfib) were exposed to 200ng/ml of recombinant GH for 24 hours. mRNA was extracted and reverse transcribed using fluorescent nucleotides (one fluorescence wavelength for control conditions, another for GH conditions). For each cell type the two cDNA probes were mixed and hybridized to a separate microarray chip containing 7074 gene transcripts (IncyteGenomics). Measurement of intensity of fluorescence at each wavelength gave the expression of each transcript under each condition. For each chip (i.e. each cell type) GH-dependent effects were assessed by comparing the signal from the two fluorophores standardised by the signal for control conditions.

Results. Under control conditions the gene expression profile was similar in the two cell types (Spearman's rho=0.98, p<0.001). We examined the 1989 transcripts which showed the 30% highest basal expression in Nfib. A GH-dependent increase in expression of at least 30% was found in 9 of these transcripts in Nfib and a decrease of similar magnitude in 0. In Lfib the corresponding figures were 39 (including 9 ESTs) and 2.4 of the transcripts which increased by 30% were GH-dependent to this degree in both cell types.

Discussion. GH effects on Nfib and Lfib showed some similarities, despite differences in GH-dependent intracellular signaling between these cell types. Some GH-dependent changes are more marked in Lfib than Nfib. This suggests that the signaling defect in Lfib includes attenuation of inhibitory influences active in Nfib. cDNA microarrarys provide a means to explore relationships between intracellular signaling and patterns of gene expression.