β2 -adrenergic receptor signaling drives prostate cancer progression by targeting the Sonic hedgehog-Gli1 signaling activation

Background: Considerable evidence suggests that the sympathetic nervous system, mainly via adrenergic signaling, contributes to prostate Cancer (PCa) progression. However, the underlying molecular mechanisms remain unknown.

Methods: The expression level of β₂ -adrenergic receptor (β₂ -AR) in tissue microarray was evaluated by immunohistochemistry. The effects of isoproterenol (ISO) or Sonic Hedgehog (Shh) signaling inhibitor on tumor growth were analyzed in proliferation and colony formation assays. The Apoptosis of cells was analyzed by flow cytometry. Small hairpin RNA-based knockdown of β₂ -AR or Gli1 was validated by Western blot analysis and Real-Time PCR. Effects of β₂ -AR on prostate carcinogenesis in vivo were observed in a mouse xenograft model. The expression levels of the indicated proteins in xenograft tissues were evaluated by immunohistochemistry. Expression levels of Shh signaling components and downstream proteins were assessed by immunoblotting.

Results: We determined that β₂ -AR was expressed at significantly higher levels in carcinoma than in normal prostate tissues. β₂ -AR signaling also played an essential role in sustaining PCa cell proliferation in vivo and in vitro. We also found that inhibition of Shh signaling or knockdown of Gli1 expression significantly restrained ISO-induced cell proliferation in vitro. ISO alleviated the Apoptosis induced by suppressing or knocking down of Gli1. The β₂ -AR agonist ISO upregulated the transcription and protein expression of target genes of Shh signaling, including c-Myc, Cyclin D1, and VEGFA. Conversely, knocking down β₂ -AR markedly suppressed the expression of Shh components in vivo and in vitro. In Gli1 knockdown cells, ISO failed to increase the expression of target genes of Shh signaling.

Conclusions: In this study, we uncovered an important role of β₂ -AR signaling in regulating the Shh pathway activity in PCa tumorigenesis and provide further insight into the mechanism of the involvement of the Hh signaling pathway. Furthermore, given the efficacy of β₂ -adrenergic modulation on PCa, our study might also add evidence for potential therapeutic options of β-blockers for PCa.