Supplementary Material for: The RNA-Binding Protein PCBP1 Functions as a Tumor Suppressor in Prostate Cancer by Inhibiting Mitogen Activated Protein Kinase 1

<b><i>Background/Aims:</i></b> Poly r(C) binding protein (PCBP) 1 or heterogeneous ribonucleoprotein (hnRNP) E1 is a RNA binding protein functional in multiple biological processes. In prostate cancer (PCa), PCBP1 loss was shown to be involved with increased stemness in PCacells; however, the underlying mechanism remains unclear. <b><i>Method:</i></b> The role of PCBP1 in prostate tumor formationwas determined by xenograft assays. Immunoprecipitationand mass spectrometry were performed to find the pathways altered after PCBP1 knockdown. Cell proliferation, migration, invasion, and soft agar colony formationassays and xenograft assays were used to determine the role of target protein pathogenesis regulation and formation of PCa. QRT-PCR was performedto quantify relative mRNA expression. <b><i>Results:</i></b> The expression of mitogen activated protein kinase 1 (MAPK1) or extracellular signal regulated kinase 2 (ERK2) was increased following PCBP1 loss. Attenuation of MAPK1 inhibited <i>in vitro</i> and <i>in vivo</i> tumorigenicity and metastasis in PCa cell line, PC3. Overexpression of MAPK1 in the PC3 cells increased the tumorigenicity and metastasis. Analysis of PCBP1 and MAPK1 mRNA levels in 25 PCa patients compared to tumor-adjacent normal tissue confirmed an inverse correlation between PCBP1 and MAPK1 expression. <b><i>Conclusions:</i></b> PCBP1 can act as a suppressor of tumor in prostate epithelial cells by inhibiting MAPK1 expression.