Id4 deficiency attenuates prostate development and promotes PIN-like lesions by regulating androgen receptor activity and expression of NKX3.1 and PTEN

Abstract

BackgroundInhibitor of differentiation 4 (Id4), a member of the helix-loop-helix family of transcriptional regulators has emerged as a tumor suppressor in prostate cancer. Id4 is expressed in the normal prostate where its expression is also regulated by androgens. In this study we investigated the effect of loss of Id4 (Id4-/-) on adult prostate morphology.MethodsHistological analysis was performed on prostates from 6-8 weeks old Id4-/-, Id4+/- and Id4+/+ mice. Expression of Id1, Sox9, Myc, androgen receptor, Akt, p-Akt, Pten and Nkx3.1 was investigated by immunohistochemistry. Androgen receptor binding on NKX3.1 promoter was studied by chromatin immuno-precipitation. Id4 was either over-expressed or silenced in prostate cancer cell lines DU145 and LNCaP respectively followed by analysis of PTEN, NKX3.1 and Sox9 expression.ResultsId4-/- mice had smaller prostates with fewer tubules, smaller tubule diameters and subtle mPIN like lesions. Levels of androgen receptor were similar between wild type and Id4-/- prostate. Decreased NKX3.1 expression was in part due to decreased androgen receptor binding on NKX3.1 promoter in Id4-/- mice. The increase in the expression of Myc, Sox9, Id1, Ki67 and decrease in the expression of PTEN, Akt and phospho-AKT was associated with subtle mPIN like lesions in Id4-/- prostates. Finally, prostate cancer cell line models in which Id4 was either silenced or over-expressed confirmed that Id4 regulates NKX3.1, Sox9 and PTEN.ConclusionsOur results suggest that loss of Id4 attenuates normal prostate development and promotes hyperplasia/dysplasia with subtle mPIN like lesions characterized by gain of Myc and Id1 and loss of Nkx3.1 and Pten expression. One of the mechanisms by which Id4 may regulate normal prostate development is through regulating androgen receptor binding to respective response elements such as those on NKX3.1 promoter. In spite of these complex alterations, large neoplastic lesions in Id4-/- prostates were not observed suggesting the possibility of mechanisms/pathways such as loss of Akt that could restrain the formation of significant pre-cancerous lesions.

Inhibitor of differentiation 4 (ID4): From development to cancer

“…In adult human tissues, ID4 expression is observed in brain, thyroid, testis and pancreas [21]. ID4 is also required for normal mammary [22] and prostate gland development [23]. …”

“…ID4 is highly expressed in osteoblasts [24], adipocytes [25], prostate epithelial cells [23] neurons [26], testicular Sertoli cells [27] and during differentiation in glial cells [28] supporting its role as a pro-differentiation factor. ID4 is also expressed in germ cells at various stages of development: spermatogonial stem cells [29], spermatocytes, pachytene spermatocytes and spermatids [30].…”

“…We have shown that ID4 is a key regulator in the normal development of various androgen dependent organs of the male genital tract in general and specifically of the prostate. Prostates from ID4-/- mice have smaller size, decreased branching morphogenesis and decreased differentiated luminal cells as demonstrated by almost complete loss of NKX3.1 expression, a marker of differentiated luminal epithelial cells [23]. A similar defect in branching morphogenesis in the developing mammary gland of ID4-/- [22] therefore appears to be a consistent mechanism.…”

ID4 controls luminal lineage commitment in normal mammary epithelium and inhibits BRCA1 function in basal-like breast cancer

“…Similarly, ID4 is expressed in hormonally regulated tissues including the breast, ovaries and prostate and is required for normal development (Shan et al 2003, Dong et al 2011, Sharma et al 2013, Best et al 2014, Junankar et al 2015. ID4 is stimulated by progesterone receptor (PR) activity through direct binding of ligand-activated PR to the ID4 promoter (Fernandez-Valdivia et al 2008).…”

Dual roles for Id4 in the regulation of estrogen signaling in the mammary gland and ovary

“…Only 20% of mice survive on an Id4-null background, following a high proportion of embryonic and post-partum lethality resulting from severe brain and neuronal abnormalities (Bedford et al, 2005;Yun et al, 2004). In the male reproductive system, Id4 loss results in significantly reduced seminal vesicle size, prostatic intraepithelial neoplasia (PIN) lesions and sterility (Sharma et al, 2013), while a recent study in the mammary gland has shown that Id4 governs ductal elongation and branching via the Id4 target p38MAPK (Dong et al, 2011). In breast epithelial cells, Id4 negatively controls expression of the key tumor suppressor Brca1 (Beger et al, 2001) and also suppresses miR335, a positive regulator of Brca1 (Heyn et al, 2011).…”