PDGFRβ and oncogenic, mutant PDGFRα D842V promote disassembly of primary cilia by a PLCγ and AURKA dependent mechanism

Abstract

Primary cilia are microtubule-based sensory organelles projecting from most quiescent mammalian cells, which disassemble in cells cultured in serum-deprived conditions upon re-addition of serum or growth factors. Platelet-derived growth factors (PDGF) are implicated in deciliation, but the specific receptor isoforms and mechanisms involved are unclear. We report that PDGFRβ promotes deciliation in cultured cells and provide evidence implicating PLCγ and intracellular Ca 2+ release in this process. Activation of wild-type PDGFRα alone did not elicit deciliation. However, expression of constitutively active PDGFRα D842V mutant receptor, which potently activates PLCγ (also known as PLCG1), caused significant deciliation, and this phenotype was rescued by inhibiting PDGFRα D842V kinase activity or AURKA. We propose that PDGFRβ and PDGFRα D842V promote deciliation through PLCγ-mediated Ca 2+ release from intracellular stores, causing activation of calmodulin and AURKA-triggered deciliation.

Cilium assembly and disassembly

“…For example, certain ciliary signalling proteins, such as Smo (a key regulator of Hh signalling) or platelet-derived growth factor receptor (PDGFR), are proto-oncogenes that are aberrantly activated at cilia in cancer 82,83 . Remarkably, whereas some types of cancer (basal cell carcinoma and medulloblastoma) are dependent on cilia 84,85 , other cancers, including melanoma and breast, pancreatic, renal, and prostate cancer, exhibit loss of cilia, most likely during the early stages of oncogenesis 86–90 .…”

Primary Cilia and Coordination of Receptor Tyrosine Kinase (RTK) and Transforming Growth Factor β (TGF-β) Signaling

“…Nevertheless, when GFP-tagged PDGFRa was expressed in RPE cells, the fusion protein was found to localize to the primary cilium ( Fig. 2B) (Nielsen et al 2015), suggesting that these cells indeed contain the machinery for targeting the receptor to this organelle. Moreover, careful examination of newly divided, cultured NIH3T3 cells revealed that PDGFRa localizes asynchronously to cilia of two sister cells, with the receptor preferentially accumulating in the cilium emanating from the cell with the oldest mother centriole (Anderson and Stearns 2009).…”

“…Subsequent studies have confirmed cilia-specific localization of PDGFRa in a range of additional cell types, including rat astrocytes and neuroblasts (Danilov et al 2009), mouse heart ventricular cells (Gerhardt et al 2013), human embryonic stem cells (Awan et al 2010), ovarian surface epithelial cells (Egeberg et al 2012), and mouse osteoblasts (Noda et al 2016). Of note, in some ciliated cell types, such as rat oligodendrocytes (Falcon-Urrutia et al 2015) and mouse heart atrial cells (Gerhardt et al 2013), PDGFRa seems to be conspicuously absent from the organelle, whereas in retinal pigment epithelial (RPE) cells, which are commonly used in ciliary studies, PDGFRa seems hardly to be expressed at all (Lei et al 2011;Nielsen et al 2015). Nevertheless, when GFP-tagged PDGFRa was expressed in RPE cells, the fusion protein was found to localize to the primary cilium ( Fig.…”

“…In addition, specific kinase-activating mutations in PDGFRa that are associated with increased PLCg signaling and development of gastrointestinal stromal tumors (GISTs), such as the PDGFRa D842V mutation (Olson and Soriano 2009;Corless et al 2011;Bahlawane et al 2015), may lead to cilia loss by triggering calmodulin and Aurora A kinase-dependent cilia disassembly ( Fig. 2A) Nielsen et al 2015). However, it remains to be determined whether cilia loss contributes to disease progression in GIST patients with the PDGFRa D842V mutation, although precursor cells of GIST are known to possess primary cilia (Castiella et al 2013).…”

“…Interestingly, patients with mutations in IGF-1 or IGF-1R were reported to suffer from microcephaly and mental retardation (Walenkamp et al 2005;Walenkamp and Wit 2006), which may be caused by defects in cilia disassembly of neural progenitor cells (Gabriel et al 2016). Of note, additional RTKs may cooperate with IGF-1R to promote cilia disassembly in a cell-or tissue-dependent manner, because in some cell types (e.g., mouse fibroblasts) significant IGF-1-induced ciliary disassembly was observed only in combination with other RTK ligands such as PDGF-AA (Jacoby et al 2009;Nielsen et al 2015). Moreover, because activation of nonciliary RTKs such as PDGFRb induces robust ciliary disassembly, at least in some cell types (Nielsen et al 2015), the signaling network(s) involved in control of ciliary disassembly and cell-cycle control is likely to be quite complex.…”