17β-Estradiol Regulates SKP2 Expression in Cultured Immature Boar Sertoli Cells Mainly via Estrogen Receptor β, cAMP-PKA and ERK1/2

Estrogen plays an important role in regulating testicular Sertoli cell number. Furthermore, S-phase kinase-associated protein 2 (SKP2) plays a central role in mammalian cell cycle progression. The objective of this study was to determine whether 17 beta-estradiol can regulate the expression of SKP2, and the Sertoli cell cycle, via estrogen receptor beta (ER beta), the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) and extracellular signal-regulated kinase (ERK1/2) pathway. When cultured immature boar Sertoli cells were treated with 17 beta-estradiol, a time-dependent increase in SKP2 mRNA and protein level was observed by real-time PCR and Western blot, and 17 beta-estradiol activity peaked at 30 mm. Treatment with ICI182780 and ER beta antagonist reduced 17 beta-estradiol-induced expression of SKP2 and proliferating cell nuclear antigen (PCNA), while increasing the protein concentration of p27(kiPl). However, the effect of ER alpha antagonist on these parameters was lower than that of 10182780 and ER beta. Forskolin had a similar effect as 17 beta-estradiol on the expression of SKP2, PCNA and p27(kipl). Rp-cAMP, H-89 and U0126 treatment reduced 17 beta-estradiol-induced changes, while H-89 also inhibited ERK1/2 activation. Therefore, 17 beta-estradiol mainly regulates SKP2 mRNA and protein expression via ER beta-cAMP-PKA and ERK1/2 activation. SKP2 and PCNA expression were positively correlated, while increased SKP2 expression likely resulted in p27(kipl) degradation.