Transformation of tissue-resident, very small embryonic-like stem cells (VSELs) into cancer stem cells (CSCs) and its role in cancer initiation via epigenetic changes.

Abstract

e15084 Background: CSCs are postulated to initiate cancer but still no consensus on their surface markers and origin. Pluripotent VSELs exist in adult tissues, express receptors for steroid and gonadotropin hormones and are possible ‘embryonic remnants’ that could initiate cancer. Methods: Neonatal exposure to diethylstilbestrol (DES) or estradiol (E2) resulted in tumor-like changes in uterus and testes of 100 days old mice. Various studies included histological changes, VSELs enumeration by flow cytometry, and a carefully selected panel of transcripts by qRT-PCR to delineate various cellular events. Mice neonatally exposed to endocrine disruption were administered XAR (a nano-formulation of resveratrol) or transplanted niche-providing mesenchymal stromal cells on D60 and studied later on D100 for reversal/prevention of cancer phenotype. Results: Both E2 and DES resulted in increased numbers of VSELs in testis (Ctrl:0.2%; E2:0.4%; DES:1.3%) and uterus (Ctrl:18.52%; E2:35.42%; DES:40.57%). An up-regulation of pluripotent transcripts ( Oct-4, Sox-2, Nanog) was detected. Oct4A (specific marker for pluripotent VSELs) was upregulated after both DES (testis > 8 folds; uterus > 15 folds) and E2 (testis > 3 folds and uterus > 10 folds) treatment. Excessive self-renewal of VSELs was associated with dysregulated expression of DNA methyltransferases (Dnmts). Dnmt1 was downregulated while Dnmt3a, Dnmt3b, and Dnmt3L were upregulated in the testis. In the uterus, Dnmts showed increased expression after both E2 and DES treatment. Marked reduction of 5mC suggested global hypomethylation and increased Igf2 and Dlk-1 suggested affected/loss of imprinting at IGF2/H19 and DLK-1/MEG3 loci. VSELs acquired CSCs phenotype with increased expression of CD166 and ALDH1. Genomic instability in CSCs was suggested by dysregulated mismatch repair axis (DNMT-1/NP95/PCNA) and repair enzymes ( Brca-1, Rad-51, Mlh-1). Reduced expression of Pten and p53 was associated with blocked differentiation. Both reversal strategies resulted in normalization of stem cells compartment, improved differentiation (spermatogenesis/adenogenesis), reduced CSC markers, and increased p53, Pten, Np95, Sirt-1 expression. Interestingly, XAR treatment resulted in downregulation of Igf2 and Dlk1. Stem cells niche was also improved as evident by increased expression of SOX9 in testis and CD90, VIMENTIN in endometrium. Conclusions: Only immortal VSELs can transmit developmental insults to adult cells. Altered epigenetic state of VSELs resulted in cancer initiation and it was possible to prevent/reverse cancer by normalizing epigenetic state of VSELs and their niche. Targeting CSCs and pushing them back into quiescent VSELs and facilitating their normal differentiation offers novel method to win the war against cancer.