GSTP is a class Glutathione S transferase GST enzyme
GSTP1 is a π-class Glutathione S-transferase (GST-π) enzyme involved in tumor suppression by protecting Agar against genomic damage mediated by various oxidants. Although the loss of GSTP1 function by hypermethylation has been reported as a common epigenetic alteration in prostate carcinogenesis (Lin et al., 2001), our study found a hypomethylation of GSTP1 in prostate grand during the neonatal period, as previously reported (Kwabi-Addo et al., 2007), and was not significantly altered upon IUL exposure to DEHP. In contrast, its mRNA expression was greatly up-regulated. It was probably because that DEHP induce the oxidative stress in prostate cells, as Erkekoglu et al. reported (Erkekoglu et al., 2011), and the induced ROS could in turn enhanced the expression of functional GSTP1 to protect cells from oxidative stress-induced damage and carcinogenesis in prostate (Nagai et al., 2004). Thus, our results were more likely to support a tumor inhibition effect of GSTP1 in prostate carcinogenesis during the fetal and neonatal period, which need to be further investigated. PTGS2, also known as cyclooxygenase-2 (COX-2), has been defined as a candidate gene for PCa susceptibility. However, it is normally undetectable in tissues, except being induced by endogenic or ectogenic stimulus. In our study, IUL exposure to DEHP activated the expression of PTGS2. The result was identical to a study documenting that DEHP elevated the expression of PTGS2 through p38 MAPK pathway and further induced allergic inflammatory response in mice (Oh and Lim, 2011). Moreover, our data suggested a significant association between PCa susceptibility and up-regulated PTGS2 mRNA during critical development period of prostate. The mechanism involved could be explained, because overexpression of PTGS2 has been reported to promote prostate carcinogenesis by increasing inflammatory response, facilitating angiogenesis and up-regulating DNA oxidation (Cohen et al., 2006). Interestingly, previous studies has occasionally reported that PTGS2 hypermethylation was associate with PCa progression (Woodson et al., 2006), but their relationship was usually assessed when precursor lesion in prostate already existed in later period of life. Moreover, Bernard et al. suggested that PCa-related genes could also aberrant hypermethylated as a function of age in normal prostate tissue (Kwabi-Addo et al., 2007). This may explain the reason why the present data did not found an aberrant methylation of PTGS2 during the early life even in DEHP treatment group. The expression of Nkx3.1 has been reported to peak between postnatal 6 and 15 days of life followed by a decline to steady-state levels thereafter, but the transient overexpression of Nkx3.1 could be completely abolished when neonatal exposure to high-dose estrogen (Prins et al., 2006). In this regard, Prins et al. suggested that the restricted expression of Nkx3.1 may serve as a key molecular to mediate the differentiation defects observed in the developmentally estrogenized prostate gland (Prins et al., 2007). Thus, although DEHP, with estrogen like effects, exposure during fetal and neonatal period did not cause an aberrantly expression of NKX3.1 in prostate, the relationship between NKX3.1 and PCa susceptibility cannot be ignored and needs further investigation. Additionally, phthalates have been reported to modulate the activity of the estrogen receptors and exert endocrine effect, but DEHP and its secondary metabolites could not activate the ESR2, as monitored by reporter gene assay (Engel et al., 2017). This was coincided with result in our study. Moreover, the present study did not show an aberrantly expression of Rassf1a in prostate after IUL exposure to DEHP. The results suggest that the DEHP-increased PCa susceptibility may not be associated with, at least, the expression of Rassf1a and ESR2 in early life. In summary, results of this study suggested that DEHP exposures during fatal and neonatal periods initiated the expression of PCa-related genes (GSTP1, PTGS2 and PSCA) early in life which might predispose the prostate to neoplasia with aging. Furthermore, based on significant association between DEHP-induced epigenomic changes early in life and the deregulated gene expression and function in the adult (Martinez-Arguelles and Papadopoulos, 2015), as well as the important role of PSCA in malignant progression of prostate cancers, the IUL exposure to DEHP-induced hypomethylation of PSCA during early life might serve as an epigenomic basis for the susceptibility of prostate carcinogenesis with aging. Given that the 6 PCa-related genes used in this study had been selected based on subjective, rather than scientifically objective criteria, and were only detected in one timepoint, the combined risk of carcinogenic susceptibility associated with other molecules or pathways should be future continuously considered.