Sprouty3 and Sprouty4, Two Members of a Family Known to Inhibit FGF-Mediated Signaling, Exert Opposing Roles on Proliferation and Migration of Glioblastoma-Derived Cells.

cells Article Sprouty3 and Sprouty4, Two Members of a Family Known to Inhibit FGF-Mediated Signaling, Exert Opposing Roles on Proliferation and Migration of Glioblastoma-Derived Cells Burcu Emine Celik-Selvi, Astrid Stütz, Christoph-Erik Mayer, Jihen Salhi, Gerald Siegwart and Hedwig Sutterlüty * Institute of Cancer Research, Department of Medicine I, Comprehensive Cancer Center, Medica University of Vienna, A-1090 Vienna, Austria * Correspondence: ; Tel.: +43-1-40160-57526 Received: 26 June 2019; Accepted: 29 July 2019; Published: 1 August 2019



 Abstract: Dysregulation of receptor tyrosine kinase-induced pathways is a critical step driving the oncogenic potential of brain cancer. In this study, we investigated the role of two members of the Sprouty (Spry) family in brain cancer-derived cell lines. Using immunoblot analyses we found essential differences in the pattern of endogenous Spry3 and Spry4 expression. While Spry4 expression was mitogen-dependent and repressed in a number of cells from higher malignant brain cancers, Spry3 levels neither fluctuated in response to serum withdrawal nor were repressed in glioblastoma (GBM)-derived cell lines. In accordance to the well-known inhibitory role of Spry proteins in fibroblast growth factor (FGF)-mediated signaling, both Spry proteins were able to interfere with FGF-induced activation of the MAPK pathway although to a different extent. In response to serum solely, Spry4 exerts its role as a negative regulator of MAPK activation. Ectopic expression of Spry4 inhibited proliferation and migration of GBM-originated cells, positioning it as a tumor suppressor in brain cancer. In contrast, elevated Spry3 levels accelerated both proliferation and migration of these cell lines, while repression of Spry3 levels using shRNA caused a significant diminished growth and migration velocity rate of a GBM-derived cell line. This argues for a tumor-promoting function of Spry3 in GBMs. Based on these data we conclude that Spry3 and Spry4 fulfill different if not opposing roles within the cancerogenesis of brain malignancies. Keywords: Sprouty proteins; brain cancer; FGF-mediated signaling; tumor suppressor; tumor promoter 1. Introduction The term brain cancer summarizes multiple subtypes of tumors originating from different tissues of the central nervous system [1]. The most prevalent type of brain tumors are gliomas which arise from glial or precursor cells. They include, among others, lower graded astrocytoma (AC) and oligodendroglioma (ODG), as well as the WHO Grade IV classified glioblastoma multiforme (GBM) and its variant gliosarcoma (GS). GBM are the most common brain tumors and patients have a poor prognosis with a five-year survival rate of only 5.6% [2]. A group of neuronal tumors arising in the central but also in the autonomic nervous system are the rare neuroblastoma (NB) which are the second most common tumors in children [3]. Like in all human cancer cells, malignant transformation in gliomas is driven by typical chromosomal changes. The Cancer Genome Atlas project identified alterations in the network regulated by receptor-tyrosine kinases (RTK) as a frequent molecular cause of these cancers. Important molecules responsible for transducing the signals like the epidermal growth Cells 2019, 8, 808; doi:10.3390/cells8080808 www.mdpi.com/journal/cells Cells 2019, 8, 808 2 of 18 factor receptor (EGFR), the phosphatidylinositol 3-kinases (PI3K), NRAS and BRAF are frequently altered to a more efficient state, while inhibitors of their activities like neurofibromin (NF1) and the Phosphatase and TENsin homolog (PTEN) are often deleted or less effective [4]. Sprouty (Spry) proteins which represent modulators of RTK-driven signaling pathways were first identified as inhibitors of fibroblast growth factor (FGF)-induced signaling in Drosophila [5]. In humans, four homologues were described [6]. In contrast to the other Spry family members which are ubiquitously expressed in all tissues [6], the Spry3 encoding gene localizes to the pseudoautosomal region 2 and its expression is rarely documented. Only in brain and glia, Spry3 expression is doubtless detected [7]. Spry proteins fulfill important functions in many RTK-mediated signal transduction cascades. Primarily, they are known to interfere specifically with MAPK-ERK activation [8–10], but in other systems they were shown to influence the PI3K pathway as well [11]. Additionally, Spry proteins are able to interfere with phospholipase C-induced pathways [12]. In contrast to their manifold inhibitory function on RTK-mediated pathways, Spry proteins are able to interact with the E3-ubiquitin ligase c-Cbl and thereby constrict the degradation of some RTKs as shown for the EGFR [13]. Considering their functions in fine tuning of the cellular response to RTK-inducing signals, members of the Spry family are good candidates for an important role in the tumorigenesis of different cells. Accordingly, Spry2 and/or Spry4 are shown to act as tumor-suppressors in cancer originated from, e.g., lung [14–16], liver [17], breast [18,19], prostate [20] and bone [21]. In other types of tumors, members of the Spry protein family fulfill a tumor-promoting task as it was demonstrated for Spry2 in colon carcinoma [22,23] and for Spry1 in rhabdomyosarcoma [24]. In brain tumors, repression of Spry2 has been shown to interfere with proliferation of GBM-derived cell lines and tumor formation [25,26]. Compatible with the tumor-promoting function of Spry2 in brain, the Spry proteins are important for other neuronal processes. Spry2 as well as Spry4 downregulation is associated with promoted axon outgrowth [27,28], and Spry1, Spry2 and Spry4 inhibit FGF-induced processes in the cerebellum [29]. Data generated in Xenopus document that Spry3 is important in regulating axon branching of motoneurons [30], and the finding that Spry3 is associated with autism susceptibility indicates a further role in the human brain [7]. In the presented study, we investigated the expression of Spry3 and Spry4 in brain cancer-derived cells and analyzed how a modulation of their expression influences the behavior of glioblastoma-derived cell lines. 2. Material and Methods 2.1. Cell Lines The astrocytoma-derived cells (SW1088) and both neuroblastoma-derived cell lines (SK-N-DZ and SK-N-FI), as well as the glioblastoma-derived cell lines DBTRG-05MG, T98G and U373 and the oligodendroglioma-derived cell line Hs683 were purchased from the American Type Culture Collection (ATCC). NMC-G1, a cell line established from an astrocytoma, and AM-38, a glioblastoma originated cell line, were obtained from the JCRB cell bank. Cell lines LN40 and LN140 were kindly provided by Dr. Tribolet (Lausanne). Cell lines BTL1529, BTL2177 and BTL53 were established from glioblastoma diagnosed patients and BTL1376 and BTL2175 from gliosarcoma patients at the Neuromed Campus in Linz (NML) as described [31]. The cell line VBT72 was establish (...truncated)