Plasma membrane sialidase NEU3 up-regulation promotes b1 integrin recycling to the plasma membrane, driving renal cell carcinoma (RCC) progression

Renal cell carcinoma (RCC) is the most common and lethal form of kidney cancer. One-third of patients have metastases at presentation, and approximately 40% of patients treated for a localized tumor develop recurrence. Treatment of advanced RCC with chemo/radiotherapy has been largely unsuccessful. In this report, we demonstrated that, in RCC, invasion and resistance to drugs are related to the up-regulation of plasma membrane sialidase, NEU3. We stably silence NEU3 in a human primary RCC cell line, CA-TC, using a lentiviral approach. We demonstrated that NEU3 silencing: a) reduced the resistance to etoposide, increasing apoptosis and, in parallel, decreasing autophagy, through an increased expression of BAX and BAD and a decreased expression of BCL-2; b) decreased the invasion potential, reducing the expression of the metalloproteases, MMP7 and MMP1. These effects are mediated by a different trafficking of β1 integrins: in NEU3 silencing cells, β1 integrins were faster internalized through caveolar endocytosis and SRC kinases activation. Then, in contrast to mock cells that rapidly recycled internalized β1 integrins to the plasma membrane, in NEU3 silencing cells, β1 integrins were directed toward lysosomes. These modifications of β1 integrin recycling were mediated by the up-regulation of RAB25 and the down-regulation of CLIC3 in NEU3 silencing cells. The increased degradation of β1 integrins induced, in turns, the down-regulation of FAK, AKT, and EGFR signaling responsible for resistance to drugs and invasion potential in RCC cells. Changes of caveolar endocytosis and β1 integrin trafficking appeared to be related to the increase of GD1a and to alteration of sphingolipid pattern consequent to NEU3 silencing. The induction of a GD1a-rich ganglioside profile in CA-TC cells by GD1a incorporation significantly reproduced some of the above effects. Therefore, NEU3 seems to be crucially involved in RCC key signaling pathways and could constitute a new therapeutic target.