V-ATPase inhibition by archazolid leads to lysosomal dysfunction resulting in impaired cathepsin B activationin vivo

Abstract

The myxobacterial agent archazolid inhibits the vacuolar proton pump V-ATPase. V-ATPases are ubiquitously expressed ATPdependent proton pumps, which are known to regulate the pH in endomembrane systems and thus play a crucial role in endo-and exocytotic processes of the cell. As cancer cells depend on a highly active secretion of proteolytic proteins in order to invade tissue and form metastases, inhibition of V-ATPase is proposed to affect the secretion profile of cancer cells and thus potentially abrogate their metastatic properties. Archazolid is a novel V-ATPase inhibitor. Here, we show that the secretion pattern of archazolid treated cancer cells includes various prometastatic lysosomal proteins like cathepsin A, B, C, D and Z. In particular, archazolid induced the secretion of the proforms of cathepsin B and D. Archazolid treatment abrogates the cathepsin B maturation process leading to reduced intracellular mature cathepsin B protein abundance and finally decreased cathepsin B activity, by inhibiting mannose-6-phoshate receptor-dependent trafficking. Importantly, in vivo reduced cathepsin B protein as well as a decreased proteolytic cathepsin B activity was detected in tumor tissue of archazolid-treated mice. Our results show that inhibition of V-ATPase by archazolid reduces the activity of prometastatic proteases like cathepsin B in vitro and in vivo.Vacuolar (H1)-ATPases (V-ATPases) are found on various membranes, including lysosomes, endosomes, vesicles and the plasma membrane. As V-ATPases are ATP-dependent proton pumps they are crucial for maintaining the pH of these compartments. Thus, they play a vital role in various cellular processes, like intracellular targeting of lysosomal enzymes, protein processing and degradation as well as receptor-mediated endocytosis.

Targeting V-ATPase in primary human monocytes by archazolid potently represses the classical secretion of cytokines due to accumulation at the endoplasmic reticulum

“…In contrast to monocytes, archazolid in vitro is instead well-documented to induce cell death in different cancer cells [15,16,18,31] and its anti-tumoral activity in vivo has recently been reported [15,32] The occurrence of V-ATPase in monocytic cells was demonstrated before [35], but the focus of VATPase research was placed on leukemia-derived cells lines (e.g., THP-1 and U937) [36] and on other differentiated cells of the monocyte/macrophage haematopoietic lineage including osteoclasts [37]. In fact, V-ATPase expression is increased during macrophage differentiation of THP-1 and U-937 [36].…”

The Function of V-ATPases in Cancer

“…Treatment with the V-ATPase inhibitor archazolid reduces cathepsin B abundance and activity in tumors in a mouse model of breast cancer, supporting the hypothesis that the V-ATPase contributes to metastasis through the promotion of protease activity (89). Reduced metastasis of breast cancer cells after V-ATPase inhibition may also be a result of the induction of anoikis or increased susceptibility to apoptosis under hypoxic conditions (51,150).…”

“…Moreover, both intracellular and plasma membrane V-ATPases may contribute to the promotion of protease activity. Intracellular V-ATPases appear to promote the activation of invasion-promoting proteases such as MMP-2 and cathepsin B within secretory compartments of breast cancer cells (59,89). In contrast, plasma membrane V-ATPases may create a local acidic microenvironment outside of the cell that promotes the activation and/or activity of proteases involved in invasion (24) (FIGURE 5).…”

Vacuolar ATPase as a potential therapeutic target and mediator of treatment resistance in cancer

“…Intracellular V‐ATPase may play a role in tumor cell invasion by either assisting in the activation of lysosomal proteases or by activating cytosolic proteins which aid in trafficking these proteases to the surface of the cell 57, 58. V‐ATPase localizes with vesicles containing the small GTPase Rab27B, which promotes secretion of proinvasive growth factors and is associated with poor prognosis in breast cancer.…”