Neuroblastoma is a malignant neoplasm of the sympathetic nervous system that affects young children. Neuroblastoma originates from neural crest cells undergoing specification and differentiation. About 40 % of high-risk neuroblastoma contain gene amplification of the transcription factor
MYCN often leading to high Mycn expression whereas about 6 % of neuroblastomas contain mutation of
ALK, the majority seen in connection to
MYCN gene amplification [
2]. Also, other mutations like
PHOX2B and
ATRX as well as epigenetic aberrations have been reported in neuroblastoma [
2]. However, although genetically unstable, the majority of neuroblastomas contain no such aberrations suggesting additional mechanisms for tumorigenesis. Also, the biological and clinical heterogeneity seen in neuroblastoma subtypes suggest the notion of neuroblastoma being a spectrum of diseases.
We show that core proteins within the non-canonical Wnt/PCP signaling cascade are differentially expressed in neuroblastoma and that the expression levels of these proteins affect neuroblastoma survival. Overexpression of
Prickle1 or
Vangl2 was coupled to decreased neuroblastoma growth and reduced expression of active β-catenin (summarized in Fig.
6c). This was also evident from analysis of expression arrays of primary neuroblastoma where high expression of
Prickle1 and
Vangl2 mRNA are significantly coupled to low-risk disease and good patient survival. Inhibiting the activity of ROCK1/2, important mediators of Rac/Rho signaling coupled to PCP activity also resulted in increased expression of
Prickle1 and inhibition of β-catenin activity. We used HA1077 and Y-27632 to inhibit the activity of ROCK in neuroblastoma cells. HA1077 was more effective in stimulating Prickle1 expression, inhibiting β-catenin activity and suppressing neuroblastoma growth as compared to Y-27632. This despite that both compounds binds to the ATP binding pocket of ROCKs with similar affinity (Ki 330 nM for HA1077 and 220–300 nM for Y-27632) leading to effective inhibition of the kinase activity [
20]. Although off-target effects have been described for both compounds [
21], we currently do not have any good explanation for these differences in the activity. In contrast to neuroblastoma cells, both non-tumorigenic neural cells and transgenic mouse embryos with overexpression of
Vangl2 in nestin-expressing cells showed increased active β-catenin and reduced differentiation. These results indicate that expression of PCP core proteins have different modes of action in neuroblastoma compared to non-tumorigenic neural cells and emphasize the complexity of the cell polarity network in different tissues. PCP signaling is fundamental for proper migration, polarity, locomotion and EMT of cells during embryonal development. Vangl2 is described to play an important role in developing CNS and mutations in Vangl2 are coupled to neural tube defects in mice and humans [
22,
23]. Cell migration, polarity and EMT are processes also important during initiation, invasion and metastasis of tumor cells. Deregulated expression of molecules within the PCP signaling cascade has been shown in cancers of different origin including mammary gland tumors, hepatocellular carcinoma, colorectal, lung and prostate cancer and leukemia [
10,
24‐
27]. However, contradictive reports indicate key molecules within the PCP signaling pathway as both tumor promoters and suppressors [
10,
28]. For instance,
Vangl1 has been shown to both inhibit colorectal carcinoma metastasis in mice but also to promote and induce colorectal cancer metastasis in the same mouse model [
29,
30]. Expression of the PCP core protein Prickle1 is downregulated in hepatocellular carcinoma whereas both Prickle1 and Vangl1 expression inhibit hepatocellular carcinoma growth in vitro [
31,
32]. It is also demonstrated in hepatocellular carcinoma that high expression of Prickle1 inhibits active β-catenin though promoting ubiquitination and degradation of Dishevelled [
31]. The observation in our study, that high expression of the PCP proteins
Prickle1 or
Vangl2 reduces the growth of neuroblastoma cells, further supports the notion that key proteins within the PCP signaling pathway may act as tumor suppressors. Similar to what we show for Prickle1, it has been reported that Scribble, another PCP protein, may inhibit β-catenin signaling and act as a tumor suppressor in mammary gland, prostate and lung cancer [
10]. Taken together, accumulating evidence suggest that PCP proteins are important regulators of several cancer hallmarks and have potential both as diagnostic biomarkers for cancer aggressiveness and as future therapeutic targets.