Glycoprotein non–metastatic melanoma protein B functions with growth factor signaling to induce tumorigenesis through its serine phosphorylation

• Published in: Cancer science Vol. 112; no. 10; pp. 4187 - 4197
• Main Authors: Wang, Chen, Okita, Yukari, Zheng, Ling, Shinkai, Yasuhiro, Manevich, Lev, Chin, Jas M., Kimura, Tomokazu, Suzuki, Hiroyuki, Kumagai, Yoshito, Kato, Mitsuyasu
• Format: Journal Article
• Language: English
• Published: Tokyo John Wiley & Sons, Inc 01.10.2021; John Wiley and Sons Inc
• Subjects: Alanine; Antibodies; Breast cancer; cancer stem cell; Chromatography; Cloning; Epidermal growth factor; Epithelial cells; Fibroblast growth factor 2; Gene expression; Glycoproteins; GPNMB; Invasiveness; Mammary gland; Melanoma; Metastases; Metastasis; Mutagenesis; Original; Peptides; Phosphatase; Phosphorylation; Protein B; Protein-tyrosine kinase receptors; Proteins; Raf protein; Serine; sphere formation; Tumorigenesis
• ISSN: 1347-9032; 1349-7006
• DOI: 10.1111/cas.15090

Breast cancer is the most common cancer among women. Glycoprotein non–metastatic melanoma protein B (GPNMB), a type I transmembrane protein that is highly expressed in many cancers, including breast cancer, has been shown to be a prognostic factor. We previously reported that GPNMB overexpression confers tumorigenic potential, as evidenced by invasive tumor growth in vivo, sphere formation, and cellular migration and invasion to non–tumorigenic mammary epithelial cells. In this study, we focused on the serine (S) residue in the intracellular domain of GPNMB (S530 in human isoform b and S546 in mouse), which is predicted to be a phosphorylation site. To investigate the roles of this serine residue, we made an antibody specific for S530‐phosphorylated human GPNMB and a point mutant in which S530 is replaced by an alanine (A) residue, GPNMB(SA). Established GPNMB(SA) overexpressing cells showed a significant reduction in sphere formation in vitro and tumor growth in vivo as a result of decreased stemness‐related gene expression compared to that in GPNMB(WT)‐expressing cells. In addition, GPNMB(SA) impaired GPNMB‐mediated cellular migration. Furthermore, we found that tyrosine kinase receptor signaling triggered by epidermal growth factor or fibroblast growth factor 2 induces the serine phosphorylation of GPNMB through activation of downstream oncoproteins RAS and RAF. In this study, we revealed that GPNMB serine phosphorylation is induced by growth factor signaling through activation of downstream oncoproteins RAS and RAF. Furthermore, we found that the serine residue is critical for tumorigenic potential, as indicated by sphere formation in vitro, tumor formation in vivo, and the enhancement of stemness‐related gene expression. In addition, we showed that the serine residue is important for EMT induction and cellular migration mediated by GPNMB.