Date of Award
Doctor of Philosophy (PhD)
Jaideep Chaudhary, Ph.D.
Valerie Odero-Marah, Ph.D.
Cimona Hinton, Ph.D.
Initial studies demonstrated that Inhibitor of DNA binding/differentiation protein 4 (Id4) acts as a tumor suppressor in prostate cancer (PCa). To further confirm and investigate the mechanism by which ID4 acts as a tumor suppressor, herein we concentrated on two different approaches. In the first approach we investigated ID4 role as a tumor suppressor by regulating AKT/PI3K pathway. In the second approach, we examined the role of Id4 in blocking the tumorogenic properties of metastatic PC3 cells. Phosphoinositide 3-kinase/Protein kinase B (PI3/AKT) pathway regulates multiple biological processes leading to cell survival, proliferation and growth in cancerous cells. We performed immunohistochemistry (IHC) to determine AKT, pAKT and PTEN protein expression in Id4 knockout mouse prostates and PCa cell lines. IHC on Id4 knockout mouse prostates demonstrated a significant decrease in PTEN expression as compared to normal mouse prostates. Consistent with decrease PTEN, the expression of pAKT expression increased. Similar pattern was observed in PCa cell lines: DU145 cells lacking Id4 had low PTEN as compared to Id4 over-expressing DU145 cells. In addition, Chromatin immunoprecipitation (ChIP) analysis also demonstrated an increase in the binding of acetylated p53 on PTEN promoter in the presence of Id4.
The second approach demonstrated the tumor suppressor function of Id4 in highly tumorogenic and metastatic PC3 cell line. Interestingly, this study demonstrated that overexpression of Id4 in PC3 cells results in decreased tumorogenecity in part through increased expression of Androgen receptor (AR) and its target genes Cyclin dependent inhibitor 1 (p21) and FK506-binding protein 51 (FKBP51). Apoptosis, migration and cell proliferation decreased in the Id4 overexpressed PC3 cells. Mice injected with PC3 + Id4 cells showed decreased tumor size and volume. IHC studies on tumor xenografts demonstrated increased levels of AR, Ki67, and p21 in Id4 overexpressed xenograft. Collectively, our data indicate that ID4 acts as tumor suppressor by regulating the levels of PTEN by prompting the binding of acetylated p53 onto PTEN promoter which eventually results in inhibiting P13K/AKT pathway. Furthermore, Id4 not only increases the expression of AR in PC3 cells but also regulates the factors responsible for AR tumor suppressor activity.
Komaragiri, Shravan Kumar, "Mechanism of Action of ID4 as a Tumor Suppressor" (2016). Electronic Theses & Dissertations Collection for Atlanta University & Clark Atlanta University. 97.