Supplementary Data supporting results of main manuscript; with other cell lines; with control experiments; includes data table Figure S1. PlGF secretion is increased in multiple cell lines after irradiation. Figure S2. PlGF mRNA expression is increased in response to IR. Figure S3. P53 is a major regulator of PlGF in response to IR. Figure S4. Generation of PlGF knockout cell lines using CRISPR/Cas9 system. Table S1. Correlation of genetic background to tumor cell lines to early PlGF expression in response to IR.
ARTICLE ABSTRACT
Placental growth factor (PlGF) is a pro-angiogenic, N-glycosylated growth factor, which is secreted under pathologic situations. Here, we investigated the regulation of PlGF in response to ionizing radiation (IR) and its role for tumor angiogenesis and radiosensitivity. Secretion and expression of PlGF was induced in multiple tumor cell lines (medulloblastoma, colon and lung adenocarcinoma) in response to irradiation in a dose- and time-dependent manner. Early upregulation of PlGF expression and secretion in response to irradiation was primarily observed in p53 wild-type tumor cells, whereas tumor cells with mutated p53 only showed a minimal or delayed response. Mechanistic investigations with genetic and pharmacologic targeting of p53 corroborated regulation of PlGF by the tumor suppressor p53 in response to irradiation under normoxic and hypoxic conditions, but with so far unresolved mechanisms relevant for its minimal and delayed expression in tumor cells with a p53-mutated genetic background. Probing a paracrine role of IR-induced PlGF secretion in vitro, migration of endothelial cells was specifically increased towards irradiated PlGF wild type but not towards irradiated PlGF-knockout (PIGF-ko) medulloblastoma cells. Tumors derived from these PlGF-ko cells displayed a reduced growth rate, but similar tumor vasculature formation as in their wild-type counterparts. Interestingly though, high-dose irradiation strongly reduced microvessel density with a concomitant high rate of complete tumor regression only in the PlGF-ko tumors.
Our study shows a strong paracrine vasculature-protective role of PlGF as part of a p53-regulated IR-induced resistance mechanism and suggest PlGF as a promising target for a combined treatment modality with RT.
