Plasma membrane-associated sialidase (NEU3) regulates progression of prostate cancer to androgen-independent growth through modulation of androgen receptor signaling

Abstract

Prostate cancers generally become androgen-independent and resistant to hormone therapy with progression. To understand the underlying mechanisms and facilitate the development of novel treatments for androgen-independent prostate cancer, we have investigated plasma membrane-associated sialidase (NEU3), the key enzyme for ganglioside hydrolysis participating in transmembrane signaling. We have discovered NEU3 to be upregulated in human prostate cancer compared with non-cancerous tissue, correlating with the Gleason score. NEU3 silencing with siRNA in prostate cancer PC-3 and LNCaP cells resulted in increased expression of differentiation markers and in cell apoptosis, but decrease in Bcl-2 as well as a progression-related transcription factor, early growth response gene (EGR-1). In androgen-sensitive LNCaP cells, forced overexpression of NEU3 significantly induced expression of EGR-1, androgen receptor (AR) and PSA both with and without androgen, the cells becoming sensitive to androgen. The NEU3-mediated induction was abrogated by inhibitors for PI-3 kinase and MAP kinase and more specifically by their silencing in the absence of androgen, being confirmed by increased phosphorylation of AKT and ERK1/2 in NEU3 overexpressing cells. NEU3 siRNA introduction caused reduction of cell growth of an androgen-independent PC-3 cells in culture and of transplanted tumors in nude mice. These data suggest that NEU3 regulates tumor progression through AR signaling, and thus be a potential tool for diagnosis and therapy of androgen-independent prostate cancer.

Knockdown of scavenger receptor Class B Type I reduces prostate specific antigen secretion and viability of prostate cancer cells

“…In addition to the transcriptional effects mentioned above, the AR may also exert non‐transcriptional effects via interaction with other signaling cascades, specifically cross‐reaction with mitogenic kinases 56–58. Signaling pathways connected to AR activation are particularly concentrated in lipid rafts and therefore, may be influenced by the loss of a cholesterol influx transporter through effects on raft content and formation 59, 60. Interestingly, statins which are HMGCR inhibitors, reduce growth and PSA production by decreasing expression and activity of the AR, an effect that seemed to be implicitly linked to suppression of the Akt/mTOR signaling pathway by perturbing the lipid raft functionality 60.…”

NEU3 Sialidase Protein Interactors in the Plasma Membrane and in the Endosomes

“…In fact, the overexpression of the human ortholog NEU3 in a mouse model induces the development of insulin-resistant diabetes mellitus (11). Also, an excessive up-regulation of NEU3 has been detected in various neoplasms, including colon (12), renal (13,14), ovarian (15), melanoma (16), and prostate cancers (17), although a down-regulation of the enzyme has been observed in acute lymphoblastic leukemia (18).…”

Phosphatidic acid‐mediated activation and translocation to the cell surface of sialidase NEU3, promoting signaling for cell migration

“…Cell homogenates or purified FLAG‐tagged NEU3 (19) were used for the measurement of sialidase activity toward GM3 at pH4.6 in 50 mM sodium acetate buffer and 6.5 in 50 mM PIPES buffer or 2‐( N ‐morpholino) ethanesulfonic acid buffer. Released sialic acids were determined by HPLC with fluorescence derivation using malononitrile as described elsewhere (6, 8). One unit of activity was defined as the amount of enzyme that cleaved 1 nmol sialic acid from the substrates in 1 hour.…”