SOX2 boosts major tumor progression genes in prostate cancer and is a functional biomarker of lymph node metastasis

Critical issues in prostate cancer (PC) are a. identification of molecular drivers of the highly aggressive neuroendocrine differentiation (NED) in adenocarcinoma, and b. early assessment of disease progression. The SRY (sex determining region Y)-box 2 gene, SOX2, is an essential embryonic stem cell gene involved in prostate tumorigenesis. Here we assessed its implications in NED and progression of PC and its diagnostic and prognostic value. Laser microdissection, qRT-PCR, quantitative Methylation-Specific PCR and immunohistochemistry were used to analyze SOX2 gene expression and regulation in 206 PC samples. Results were examined according to the patient's clinical pathological profile and follow-ups. Functional studies were performed using PC cells transfected to overexpress or silence SOX2. SOX2 was consistently downregulated in PC, except in cell clusters lying within lymph node (LN)-positive PC. Multivariate analysis revealed that SOX2 mRNA expression in the primary tumor was significantly associated with LN metastasis. When SOX2 mRNA levels were ≥1.00, relative to (XpressRef) Universal Total RNA, adjusted Odds Ratio was 24.4 (95% CI: 7.54-79.0), sensitivity 0.81 (95% CI: 0.61-0.93) and specificity 0.87 (95% CI: 0.81-0.91). Patients experiencing biochemical recurrence had high median levels of SOX2 mRNA. In both PC and LN metastasis, SOX2 and NED marker, Chromogranin-A, were primarily co-expressed. In PC cells, NED genes were upregulated by SOX2 overexpression and downregulated by its silencing, which also abolished SNAI2/Slug dependent NED. Moreover, SOX2 upregulated neural CAMs, neurotrophins/neurotrophin receptors, pluripotency and epithelial-mesenchimal transition transcription factors, growth, angiogenic and lymphangiogenic factors, and promoted PC cell invasiveness and motility. This study discloses novel SOX2 target genes driving NED and spread of PC and proposes SOX2 as a functional biomarker of LN metastasization for PC.