IMPE Abstracts

The accelerated growth phase observed during puberty depends on the combined effects of the somatotropic and gonadotropic axes. Our previous studies have demonstrated that relatively low concentrations of estradiol (20 pg/mL) and high concentrations of testosterone (10 ng/mL), potentiate the JAK2/STAT5 signaling pathway induced by GH in the human hepatic cell line (HEPG2). It is not known whether these effects are direct, or are mediated through the suppressors of cytokine signaling (SOCS) proteins.

Aim: To evaluate the effects of varying concentrations of estradiol (E₂) and testosterone (T) on the protein content of SOCS1 and SOCS2 induced by GH in HEPG2 cells.

Methods: HEPG2 cells were grown in a steroid free medium. At 80% confluence, they were treated with or without different concentrations of E₂ (20, 50, 100 pg/mL), or T (1, 5, 10 ng/mL), and were subsequently stimulated with rhGH 40 ng/mL for 15 min. SOCS1, SOCS2 and GAPDH were analyzed in the cytoplasmic cell compartment by Western immunoblotting. The data were expressed as arbitrary units (AU) and analyzed by ANOVA Test and expressed as mean ± SEM. * P< 0.05 was considered significantly different.

Results: SOCS1 (0.56±0.03 AU) and SOCS2 (0.50±0.02 AU) protein levels after rhGH stimulation were similar to the content obtained under basal conditions (0.48±0.006 AU). Co-stimulation with E₂, the low concentration (20 pg/mL) increased the content of SOCS1 (0.65±0.2 AU, * P<0.05), effect not observed with the higher concentrations. The protein levels of SOCS2 were maintained (0.56±005 AU) at all concentrations of E₂ studied (20, 50, 100 pg/mL) after co-stimulation with rhGH. Higher concentrations of T (5 ng/mL and 10 ng/mL) showed decreased SOCS1 and SOCS2 protein contents when compared with rhGH levels (0.48±0.02 AU); these levels were lower at the highest concentration of T studied (0.27±0.03 and 0.21±0.01 AU vs. 0.48±0.02 AU, respectively; * P<0.05). These effects on SOCS1 and SOCS2 were not observed at the lowest concentration of T studied (1 ng/mL).

Conclusion: Estradiol and testosterone may modulate the regulation of the GH signaling pathway through the SOCS proteins. Under physiological concentrations, estradiol increases SOCS1 protein content, and maintains SOCS2 protein content. As testosterone concentrations increase, SOCS1 and SOCS2 protein content decrease. This fine interplay between sex steroids and SOCS proteins may explain how these hormones modulate GH sensitivity.