Abstract 4377: The Golgi protein GLG1 coordinates ARF3 activation in tumor cells.

Abstract

Abstract Increasing evidence suggests that endocytosis and membrane trafficking are deregulated in cancer cells. Because of their dependence on selected signaling pathways, tumor cells may need to rely on accelerated receptor recycling and increased secretion of a variety of molecules such as matrix components, adhesion molecules and growth factors. Mass spectrometry analysis of proteins associated with separase, recently shown to be an important regulator of membrane trafficking, identified the Golgi apparatus protein 1 (GLG1). GLG1 is primarily known as an E-selectin ligand that mediates the initial step of tethering and rolling of leukocytes on vascular endothelium. We therefore addressed the possibility that GLG1 could play a similar role in circulating tumor cells, facilitating arrest and extravasation into adjacent tissues. Consistent with this possibility, tail vein injection of stably GLG1-depleted tumor cells into NOD/SCID mice resulted in reduced numbers of metastatic nodules. Moreover, metastatic tumor growth was almost exclusively intravascular, indicating impaired extravasation of tumor cells. Further investigation, however, showed that, in tumor cells, GLG1 is almost exclusively localized to the Golgi apparatus, challenging the notion that it plays a direct role in mediating tumor cell adhesion to endothelium as in leukocytes. To elucidate the molecular mechanisms by which GLG1 could affect tumor cell migration through interactions at the Golgi level, we conducted various experiments using GLG1-depleted human tumor cell lines. Transient silencing of GLG1 by siRNA was observed to modify cell shape (elongated morphology), to reduce migration of a range of tumor cell lines and to markedly alter Golgi architecture. Interestingly, subsequent experiments led to the identification of a new interactor of GLG1, the Brefeldin A-inhibited guanine nucleotide-exchange protein 1 (BIG1), an ARF-GEF required to initiate membrane vesicle formation at the trans-Golgi compartment by promoting guanine-nucleotide exchange on ARF1 and ARF3. GLG1 was shown to participate in BIG1 and ARF3 recruitment to the Golgi membrane and subsequent ARF3 activation. Surprisingly, the observed morphological disruption of the Golgi apparatus and reduced ARF3 activation did not affect the secretory pathway in general, but rather seemed to impair secretion of selected molecules including MMP-9. Taken together, our observations provide insight into a novel and specific role of GLG1 in tumor progression by affecting, thanks to its privileged position in the secretory pathway, trafficking of key molecules implicated in cell migration. Citation Format: Anne Planche. The Golgi protein GLG1 coordinates ARF3 activation in tumor cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4377. doi:10.1158/1538-7445.AM2013-4377