RESUMO
Although signal transduction of transforming growth factor-betas (TGF-ßs) is well characterized in individual cell types, data about TGF-ß signaling in a cellular context is still scarce. In this study, we used ex vivo tubule cultures from adult rat testis to investigate TGF-ß signaling. We show for the first time in testicular tubules, that TGF-ßs also signal via the BMP type I receptors, with ALK2 used by TGF-ß1 and ALK3 and ALK6 by TGF-ß2. This signal transduction is mediated via Smad3 as well as via Smad1. In contrast, BMPs (BMP2 and BMP7) do not signal via the high-affinity type I and type II TGFß receptors, TBR1 or TBR2. Furthermore, treatment of tubule cultures with either TGF-ß1 or TGF-ß2 had profound significant stimulatory effects on secretion of plasminogen activator-1 (PAI-1) through utilization of TGF-ß and BMP receptors. Specific inhibitors for either TBR1 or BMP receptors yielded nearly complete inhibition of TGF-ß signaling. The TBR1-TBR2 signalosome was detected with Duolink upon stimulation with either TGF-ß1 or TGF-ß2, predominantly in spermatogenic cells of the adult rat testis, particularly in elongated spermatids. In summary, this examination of intact rat testicular tubules demonstrated for the first time that TGF-ßs signal mainly through TBR1 and TBR2 but also use BMP receptors, including for secretion of PAI-1. Whereas ALK2 participates in the TGF-ß1-induced TBR1-TBR2 signalosome, ALK3 and ALK6 are involved in signaling of TGF-ß2. Detection of the TBR1-TBR2 signalosome in late spermiogenic cells indicates a post-meiotic activity.
