Na⁺/H⁺ Exchangers and RhoA Regulate Acidic Extracellular pH‐Induced Lysosome Trafficking in Prostate Cancer Cells

Abstract

Acidic extracellular pH (pHe) is a common feature of the tumor microenvironment and has been implicated in tumor invasion through the induction of protease secretion. Since lysosomes constitute the major storehouse of cellular proteases, the trafficking of lysosomes to the cell periphery may be required in order to secrete proteases. We demonstrate that a pHe of 6.4-6.8 induced the trafficking of lysosomes to membrane protrusions in the cell periphery. This trafficking event depended upon the PI3K pathway, the GTPase RhoA and sodium-proton exchange activity, resulting in lysosomal exocytosis. Acidic pHe induced a cytoplasmic acidification (although cytoplasmic acidification was not sufficient for acidic pHe-induced lysosome trafficking and exocytosis) and inhibition of NHE activity with the amiloride derivative, EIPA or the anti-diabetic agent troglitazone prevented lysosome trafficking to the cell periphery. Interestingly, using the more specific NHE1 and NHE3 inhibitors, cariporide and s3226 respectively, we show that multiple NHE isoforms are involved in acidic pHe-induced lysosome trafficking and exocytosis. Moreover, in cells expressing NHE1 shRNA, although basal NHE activity was decreased, lysosomes still underwent acidic pHe-induced trafficking, suggesting compensation by other NHE family members. Together these data implicate proton exchangers, especially NHE1 and NHE3, in acidic pHe-induced lysosome trafficking and exocytosis.

HGF-induced invasion by prostate tumor cells requires anterograde lysosome trafficking and activity of Na+-H+ exchangers

“…1A,B illustrates the ability of HGF to induce cell scattering and the trafficking of LAMP-1-positive vesicles to the cell periphery. Using previously described software to measure and quantify the distance of lysosomes from the cell nucleus (Glunde et al, 2003;Steffan et al, 2009), we confirmed that HGF quantitatively induces the movement of LAMP-1-positive vesicles to the periphery, compared with untreated cells (Fig. 1C).…”

Regulation of invadopodia by the tumor microenvironment

“…107,108 In prostate cancer cells, NHE-1 activity promotes lysosomal fusion to invadopodia; these lysosomes then release cathepsin B to facilitate ECM proteolysis. 109 This lysosomal-trafficking mechanism is not restricted to invadopodia; similar effects have been observed in osteoclast and phagocytic podosomes, which could also be modulated by extracellular pH. 110,111 Thus, the pH of the tumor microenvironment regulates the proteolytic activity of invadopodia/podosomes through direct (protease expression and trafficking) and indirect (protease activation) mechanisms to affect cancer cell migration and invasion.…”

Heregulin (Neuregulin)/HER3 signalling increases invasive behaviour of HER2-positive breast cancer cells

“…4.4). Steffan et al showed that suppression of PI3K/Akt cascade using LY294002, a specific inhibitor for this network, diminishes lysosomal exocytosis and secretion of cathepsin B into the media of prostate cancer cells (Steffan, Snider, Skalli, Welbourne, & Cardelli, 2009). In harmony, our data suggests that activation of PI3K/Akt by HRG might be one mechanism thereby HRG increased secretion of cathepsin B into the media of HER2+ luminal breast cancer cell lines.…”