Unknown,Transcriptomics,Genomics,Proteomics

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HER2 and EGFR dependent activation of RalA in breast cancer

ABSTRACT: Activated HER2 and EGFR stimulate the Ras small GTPases, which in turn primarily activate the MAPK, PI3K-Akt and RalGEF-Ral pathways. While activation of the MAPK and PI3K-Akt pathways downstream of HER2 and EGFR promote mammary tumorigenesis, little is known regarding the role of the RalGEF-Ral pathway. RalGEFs convert the small GTPases RalA and RalB to an active GTP-bound state. Of the two proteins, only activated RalA is transforming, while RalB is more important for cell motility, and hence we investigated the role of RalA in HER2-overexpressing and EGFR-positive breast cancer. We now report that shRNA-mediated knockdown of RalA reduced the in vitro transformed growth and in vivo tumorigenic growth of MDA-MB-231 human breast cancer cells, while knockdown of RalB reduced migration and invasion. Lastly, we demonstrate that expression of activated HER2 increases RalA-GTP levels, and that a number of genes associated with activated RalA are elevated in tumor compared to normal mammary tissue. Taken together, these results suggest a possible role for RalA in mammary tumorigenesis. Four independent cultures of HEK-HT cells stably infected with a retrovirus confirmed to expressed RalAQ72L and four independent cultures of HEK-HT cells stably infected with a control retrovirus RalA activation expression analysis

ORGANISM(S): Homo sapiens

SUBMITTER: David Hsu

PROVIDER: E-GEOD-19295 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Abstract: RAS-like (RAL) GTPases function in Wnt signalling-dependent intestinal stem cell proliferation and regeneration. Whether RAL proteins work as canonical RAS effectors in the intestine, and the mechanisms of how they contribute to tumorigenesis remain unclear. Here, we show that RAL GTPases are necessary and sufficient to activate EGFR/MAPK signalling in the intestine. We identify non-canonical roles of RAL GTPases not as RAS effectors, but rather by acting upstream of RAS activation via induction of EGFR internalisation . Knocking down Drosophila RalA from intestinal stem and progenitor cells leads to increased levels of plasma membrane-associated EGFR and decreased MAPK pathway activation. Importantly, in addition to impacting stem cell proliferation and damage-induced intestinal regeneration, this function of RAL GTPases drives EGFR-dependent tumorigenic growth in the intestine and in human mammary epithelium. Altogether, our results reveal previously unrecognised cellular and molecular contexts where RAL GTPases become essential mediators of EGFR-driven tissue homeostasis and malignant transformation. Results: RalA is required within ISCs to induce midgut adult midgut regeneration following damage by oral infection with Erwinia carotovora carotovora 15 (Ecc15) (Johansson et al., 2019). To achieve a global view of intestinal pathways affected by RalA, we performed a transcriptomic analysis by RNAseq of whole midguts from vehicle treated (Mock) or damaged (Ecc15 fed) control animals or following RalA knockdown in intestinal stem and progenitor cells using the escargot-gal4 driver (ISC/EB>) (Micchelli and Perrimon, 2006). Consistent with its effect on ISC proliferation (Johansson et al., 2019), RalA knockdown significantly impaired damage-induced upregulation of cell cycle genes in the midgut. Additionally, levels of multiple transcriptional targets of the EGFR/MAPK pathway (Golembo et al., 1996; Hsu et al., 2001; Jin et al., 2015; Meng and Biteau, 2015), such as argos (aos), rhomboid (rho), Sox21a and string (stg) were increased following Ecc15 infection in control midguts. The upregulation of these target genes was significantly impaired upon RalA knockdown.

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HER2 and EGFR dependent activation of RalA in breast cancer

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