Estradiol and 1α,25(OH)2 vitamin D3 share plasma membrane downstream signal transduction through calcium influx and genomic activation in immature rat testis

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The aim of this study was to investigate the rapid response pathway and gene and protein expression profiles of the rat testis in response to estradiol (E2) and 1α,25(OH)2 vitamin D3 (1,25-D3), to understand how they mediate their effects on the first spermatogenic wave. To do this, we compared the effects of 1,25-D3 and E2 on 45calcium(Ca2+) uptake and the involvement of estrogen receptors (ESR) in their rapid responses. Additionally, we studied the downstream signal transduction effects of 1,25-D3 and E2 on cyclin A1/B1 and cellular cycle protein expression. As previously observed for 1,25-D3, E2 also increased 45Ca2+ uptake in immature rat testes via voltage-dependent Ca2+ channels, Ca2+-dependent chloride channels and via the activation of protein kinase C, protein kinase A and mitogen-activated protein kinase kinase (MEK). Elevated aromatase expression by testes was observed in the presence of 1,25-D3 and both hormones decreased ESR mRNA expression. Furthermore, 1,25-D3 and E2 diminished cyclin A1 mRNA expression, but E2 did not affect cyclin B1 mRNA levels. Consistent with these findings, the immunocontent of cyclin A1 and B1 in the testes was also increased by 1,25-D3 and E2. 1,25-D3 increased expressions of the p16 and p53 proteins, supporting the anti-proliferative and pro-apoptotic properties of 1,25-D3, while E2 also augmented p16. Data indicate that both hormones trigger rapid responses at the plasma membrane that may control the expression of gene and proteins related to cell cycle regulation, and thereby modulate spermatogenesis.