Calreticulin Regulates VEGF-A in Neuroblastoma Cells

Calreticulin (CRT) has been previously correlated with the differentiation of neuroblastoma (NB), implying a favorable prognostic factor. Vascular endothelial growth factor (VEGF) has been reported to participate in the behavior of NB. This study investigated the association of CRT and VEGF-A in NB cells. The expressions of VEGF-A and HIF-1α, with overexpression or knockdown of CRT, were measured in three NB cells (SH-SY5Y, SK-N-DZ, and stNB-V1). An inducible CRT NB cell line and knockdown CRT stable cell lines were also established. The impacts of CRT overexpression on NB cell apoptosis, proliferation, and differentiation were also evaluated. We further examined the role of VEGF-A in the NB cell differentiation via VEGF receptor blockade. Constitutive overexpression of CRT led to NB cell differentiation without proliferation. Thus, an inducible CRT stNB-V1 cell line was generated by a tetracycline-regulated gene system. CRT overexpression increased VEGF-A and HIF-1α messenger RNA (mRNA) expressions in SH-SY5Y, SK-N-DZ, and stNB-V1 cells. CRT overexpression also enhanced VEGF-A protein expression and secretion level in conditioned media in different NB cell lines. Knockdown of CRT decreased VEGF-A and HIF-1α mRNA expressions and lowered VEGF-A protein expression and secretion level in conditioned media in different NB cell lines. We further demonstrated that NB cell apoptosis was not affected by CRT overexpression in stNB-V1 cells. Nevertheless, overexpression of CRT suppressed cell proliferation and enhanced cell differentiation in stNB-V1 cells, whereas blockage of VEGFR-1 markedly suppressed the expression of neuron-specific markers including GAP43, NSE2, and NFH, as well as TrkA, a molecular marker indicative of NB cell differentiation. Our findings suggest that VEGF-A is involved in CRT-related neuronal differentiation in NB. Our work may provide important information for developing a new therapeutic strategy to improve the outcome of NB patients.