Inhibitor of differentiation 4 (Id4) is a potential tumor suppressor in prostate cancer

Abstract

BackgroundInhibitor of differentiation 4 (Id4), a member of the Id gene family is also a dominant negative regulator of basic helix loop helix (bHLH) transcription factors. Some of the functions of Id4 appear to be unique as compared to its other family members Id1, Id2 and Id3. Loss of Id4 gene expression in many cancers in association with promoter hypermethylation has led to the proposal that Id4 may act as a tumor suppressor. In this study we provide functional evidence that Id4 indeed acts as a tumor suppressor and is part of a cancer associated epigenetic re-programming.MethodsData mining was used to demonstrate Id4 expression in prostate cancer. Methylation specific polymerase chain reaction (MSP) analysis was performed to understand molecular mechanisms associated with Id4 expression in prostate cancer cell lines. The effect of ectopic Id4 expression in DU145 cells was determined by cell cycle analysis (3H thymidine incorporation and FACS), expression of androgen receptor, p53 and cyclin dependent kinase inhibitors p27 and p21 by a combination of RT-PCR, real time-PCR, western blot and immuno-cytochemical analysis.ResultsId4 expression was down-regulated in prostate cancer. Id4 expression was also down-regulated in prostate cancer line DU145 due to promoter hyper-methylation. Ectopic Id4 expression in DU145 prostate cancer cell line led to increased apoptosis and decreased cell proliferation due in part by an S-phase arrest. In addition to S-phase arrest, ectopic Id4 expression in PC3 cells also resulted in prolonged G2/M phase. At the molecular level these changes were associated with increased androgen receptor (AR), p21, p27 and p53 expression in DU145 cells.ConclusionThe results suggest that Id4 acts directly as a tumor suppressor by influencing a hierarchy of cellular processes at multiple levels that leads to a decreased cell proliferation and change in morphology that is possibly mediated through induction of previously silenced tumor suppressors.

Inhibitor of DNA Binding 4 (ID4) Regulation of Adipocyte Differentiation and Adipose Tissue Formation in Mice

“…In apparent contrast to this inhibitory role for the Id family of genes, a more limited number of observations have suggested a role for ID family members in supporting lineage-specific differentiation (18,22,34,36,37). Both ID2 and ID4 have been shown to be induced in various cell culture systems during adipocyte differentiation in vitro (18,22).…”

Silencing of the inhibitor of DNA binding protein 4 (ID4) contributes to the pathogenesis of mouse and human CLL

“…11 Members of this family lack a DNA binding domain but retain the ability to bind and thus inhibit the function of other bHLH proteins. Such binding predominately results in a tumor suppressor role of ID4 in colorectal, 12 prostate, 13,14 and gastric 15 cancers, whereas in breast 16 and bladder 17 cancer, it has oncogenic features. [16][17][18] In a study that used an interleukin-15 transgenic mouse model of natural killer (NK) cell leukemia, the authors demonstrated that ID4 was silenced by methylation in transformed lymphocytes.…”

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

“…ID4 acts as a tumour suppressor, for example, in the normal prostate where it is highly expressed; this expression decreases in prostate cancer in a stage-dependent manner as a result of ID4 promoter hypermethylation (Carey et al 2009, Sharma et al 2012. High-grade tumours are associated with the absence of ID4 expression (Carey et al 2009, Sharma et al 2012. In this context, ID4 exerts anti-proliferative effects, in part, by increasing expression of the classical tumour suppressor genes p27 and p21 (Carey et al 2009).…”

“…ID4 effects varied outcomes in cell proliferation and differentiation depending on the availability of cofactors, and hence, play either a tumour suppressive or oncogenic function. ID4 acts as a tumour suppressor, for example, in the normal prostate where it is highly expressed; this expression decreases in prostate cancer in a stage-dependent manner as a result of ID4 promoter hypermethylation (Carey et al 2009, Sharma et al 2012. High-grade tumours are associated with the absence of ID4 expression (Carey et al 2009, Sharma et al 2012.…”

“…High-grade tumours are associated with the absence of ID4 expression (Carey et al 2009, Sharma et al 2012. In this context, ID4 exerts anti-proliferative effects, in part, by increasing expression of the classical tumour suppressor genes p27 and p21 (Carey et al 2009). This work highlights the divergent and context-dependent roles of ID4 in different hormone-dependent cancers.…”