Silencing of plasma membrane sialidase Neu3 reduces apoptosis resistance and metalloproteases expression in renal cell carcinoma

Plasma membrane sialidase, Neu3, specifically hydrolyzing gangliosides, strictly modulates the sialosphingolipid pattern of the cell membrane and plays crucial roles in the regulation of surface functions and signaling. The up-regulation of Neu3 has been documented as a key alteration in carcinogenesis and has been described also in renal cell carcinomas (RCCs). In order to determine the impact of this feature on RCC pathogenesis, we stably silence Neu3 sialidase in a human primary RCC cell line, CA-TC, using a lentiviral approach. Our results demonstrated that Neu3 silencing: a) increased proliferation rate (+48% as [3H]thymidine incorporation) but reduced the resistance toward apoptosis induced by the chemotherapeutical drug, etoposide, increasing the expression of Bax and Bad and decreasing the expression of Bcl-2; b) decreased the expression of the metalloproteases, MMP7 (-95%) and MMP1 (-75%); c) reduced the activation of AKT and EGFR. Neu3 silencing deeply changed the sialosphingolipid pattern of CA-TC, mainly increasing GD1a ganglioside content (+65%). The induction of a GD1a-rich ganglioside profile in CA-TC cells by GD1a incorporation significantly reproduced some of the above effects, suggesting a key role of GD1a in these events. Therefore, Neu3 seems to be crucially involved in RCC response to drugs and invasiveness and could constitute a new therapeutic target.