Effects of Wnt-β-Catenin Signaling and Sclerostin on the Phenotypes of Rat Pheochromocytoma PC12 Cells

Pheochromocytomas and paragangliomas (PPGLs) are classified into 3 major categories with distinct driver genes: pseudohypoxia, kinase signaling, and Wnt-altered subtypes. PPGLs in the Wnt-altered subtype are sporadic and tend to be aggressive with metastasis, where somatic gene fusions affecting mastermind-like 3 (MAML3) and somatic mutations in cold shock domain containing E1 (CSDE1) cause overactivation of Wnt-β-catenin signaling. However, the relation between Wnt-β-catenin signaling and the biological behavior of PPGLs remains unexplored. In rat pheochromocytoma PC12 cells, Wnt3a treatment enhanced cell proliferation and suppressed mRNA expression of tyrosine hydroxylase (TH), the rate-limiting enzyme of catecholamine biosynthesis, and dopamine secretion. We identified the expression of sclerostin in PC12 cells, which is known as an osteocyte-derived negative regulator for Wnt signaling-driven bone formation. Inhibition of endogenous Wnt pathway by XAV939 or sclerostin resulted in attenuated cell proliferation and increased TH expression. Furthermore, Wnt3a pretreatment suppressed bone morphogenetic protein (BMP)-induced Smad1/5/9 phosphorylation whereas BMPs enhanced sclerostin expression in PC12 cells. In the Wnt-altered subtype, the increased Wnt-β-catenin pathway may contribute the aggressive clinical behavior with reduced catecholamine production. Furthermore, upregulated expression of sclerostin by BMPs may explain the osteolytic metastatic lesions observed in metastatic PPGLs.