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RAL GTPases mediate multiple myeloma cell survival and are activated independently of oncogenic RAS.

ABSTRACT: Oncogenic RAS provides crucial survival signaling for up to half of multiple myeloma cases, but has so far remained a clinically undruggable target. RAL is a member of the RAS superfamily of small GTPases and is considered to be a potential mediator of oncogenic RAS signaling. In primary multiple myeloma, we found RAL to be overexpressed in the vast majority of samples when compared with pre-malignant monoclonal gammopathy of undetermined significance or normal plasma cells. We analyzed the functional effects of RAL abrogation in myeloma cell lines and found that RAL is a critical mediator of survival. RNAi-mediated knockdown of RAL resulted in rapid induction of tumor cell death, an effect which was independent from signaling via mitogen-activated protein kinase, but appears to be partially dependent on Akt activity. Notably, RAL activation was not correlated with the presence of activating RAS mutations and remained unaffected by knockdown of oncogenic RAS. Furthermore, transcriptome analysis yielded distinct RNA expression signatures after knockdown of either RAS or RAL. Combining RAL depletion with clinically relevant anti-myeloma agents led to enhanced rates of cell death. Our data demonstrate that RAL promotes multiple myeloma cell survival independently of oncogenic RAS and, thus, this pathway represents a potential therapeutic target in its own right.

SUBMITTER: Seibold M

PROVIDER: S-EPMC7556628 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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RAL GTPases mediate multiple myeloma cell survival and are activated independently of oncogenic RAS.

Seibold Marcel M Stühmer Thorsten T Kremer Nadine N Mottok Anja A Scholz Claus-Jürgen CJ Schlosser Andreas A Leich Ellen E Holzgrabe Ulrike U Brünnert Daniela D Barrio Santiago S Kortüm Martin K MK Solimando Antonio G AG Chatterjee Manik M Einsele Hermann H Rosenwald Andreas A Bargou Ralf C RC Steinbrunn Torsten T

Haematologica 20200901 9

Oncogenic RAS provides crucial survival signaling for up to half of multiple myeloma cases, but has so far remained a clinically undruggable target. RAL is a member of the RAS superfamily of small GTPases and is considered to be a potential mediator of oncogenic RAS signaling. In primary multiple myeloma, we found RAL to be overexpressed in the vast majority of samples when compared with pre-malignant monoclonal gammopathy of undetermined significance or normal plasma cells. We analyzed the func ...[more]

PMID: 33054056

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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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RAL GTPases mediate multiple myeloma cell survival and are activated independently of oncogenic RAS.

Publications

RAL GTPases mediate multiple myeloma cell survival and are activated independently of oncogenic RAS.

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