The Arf-like GTPase Arl8b is essential for three-dimensional invasive growth of prostate cancer in vitro and xenograft formation and growth in vivo

Abstract

Cancer is a multistep process that requires cells to respond appropriately to the tumor microenvironment, both in early proliferative stages and in later invasive disease. Arl8b is a lysosome localized Arf-like GTPase that controls the spatial distribution of lysosomes via recruitment of kinesin motors. Common features of the tumor microenvironment such as acidic extracellular pH and various growthfactors stimulate lysosome trafficking to the cell periphery (anterograde), which is critical for tumor invasion by facilitating the release of lysosomal proteases to promote matrix remodeling. Herein we report for the first time that Arl8b regulates anterograde lysosome trafficking in response to hepatocyte growth factor, epidermal growth factor, and acidic extracellular pH. Depletion of Arl8b results in juxtanuclear lysosome aggregation, and this effect corresponds with both diminished invasive growth and proteolytic extracellular matrix degradation in a three-dimensional model of prostate cancer. Strikingly, we found that depletion of Arl8b abolishes the ability of prostate cancer cells to establish subcutaneous xenografts in mice. We present evidence that Arl8b facilitates lipid hydrolysis to maintain efficient metabolism for a proliferative capacity in low nutrient environments, suggesting a likely explanation for the complete inability of Arl8b-depleted tumor cells to grow in vivo. In conclusion, we have identified two mechanisms by which Arl8b regulates cancer progression: 1) through lysosome positioning and protease release leading to an invasive phenotype and 2) through control of lipid metabolism to support cellular proliferation. These novel roles highlight that Arl8b is a potential target for the development of novel anti-cancer therapeutics.

The Rab7 effector PLEKHM1 binds Arl8b to promote cargo traffic to lysosomes

“…Arl8b-mediated lysosome positioning at the cell periphery regulates diverse cellular processes, including amino acid sensing, antigen presentation, cell migration, and cancer metastasis (Garg et al, 2011;Korolchuk et al, 2011;Schiefermeier et al, 2014;Dykes et al, 2016). Our study indicates that Arl8b effectors-SKIP and PLE KHM1 play opposing roles in regulating lysosome distribution.…”

Zinc finger E‐box binding homeobox‐1 (Zeb1) drives anterograde lysosome trafficking and tumor cell invasion via upregulation of Na+/H+ Exchanger‐1 (NHE1)

“…To induce JLA, DU145 mesenchymal cells were transduced with lentivirus-delivered Non Target (NT) shRNA or shRNA targeting the ADP-Ribosylation factor like protein 8b (Arl8b), an Arf-like GTPase that recruits kinesin 1 to lysosomes. Depletion of Arl8b results in a tight clustering of lysosomes near the microtubule organizing center [32,37,38]. Immunoblot analysis confirmed knockdown (KD) of Arl8b (Figure 2A).…”

Mechanisms and functions of lysosome positioning

“…Secreted acid hydrolases are thought to degrade the extracellular matrix, facilitating cell migration and invasion (Mohamed and Sloane, 2006;Dykes et al, 2016). Transport of the transmembrane type 1 matrix metalloproteinase (MT1-MMP, also known as MMP14) from late endosomes to plasma membrane invadopodia also contributes to cancer cell invasiveness and metastasis (Monteiro et al, 2013;Macpherson et al, 2014).…”