Expression And Functional Implication Of Klf5in Mouse Prostate Epithelial Cells And Its Tumor Suppressor Role In Prostate Cancer

Prostate cancer is one of the most common malignancies and a leading cause of cancer death. It is generally recognized that molecular abnormalities that enhance cell proliferation and/or interfere with cell differentiation transform a normal epithelial cell to a cancer cell, yet the molecular events that underlie normal epithelial homeostasis and malignant transformation are still not well understood.KLF5is a basic transcription factor that regulates multiple biological processes. While it inhibites the proliferation of transformed cancer cells, likely due to its function as an effector of TGF-β in the inhibition of cell proliferation, KLF5is unacetylated and promotes cell proliferation in the absence of TGF-β. KLF5was identified as a tumor suppressor in prostate cancer, yet such a role has not been examined in an in vivo model.In this study, we firstly evaluated the expression and function of KLF5in prostatic epithelial homeostasis and tumorigenesis using mouse prostates and human prostate epithelial cells in3-D culture. Histological and molecular analyses demonstrated that unacetylated-Klf5was expressed in basal or undifferentiated cells, whereas acetylated-Klf5was expressed primarily in luminal and/or differentiated cells. Androgen depletion via castration increased both the level of Klf5expression and the number of Klf5-positive cells in the remaining prostate. Functionally, knockdown of KLF5in the human RWPE-1prostate cell line decreased the number of spheres formed in3-D culture.In addition, knockout of Klf5in prostate epithelial cells, mediated by probasin promoter-driven Cre expression, did not cause neoplasia but promoted cell proliferation and induced hyperplasia when one Klf5allele was knocked out. Knockout of both Klf5alleles however, caused apoptosis rather than cell proliferation in the epithelium. In castrated mice, knockout of Klf5resulted in more severe shrinkage of the prostate.We further introduced the loss of Pten as a cancer promoting factor, and double knocked out Klf5and Pten in mouse prostate. Loss of Klf5significantly accelerated the emergence and progression of mPIN in Pten+/-context. In Pten-/-mice, the loss of Klf5dramatically promoted the proliferation of prostate epithelial cells, enabling the prostate to form larger bulks of tumor with eliminated luminal structure. More severe cancer-related histopathologic and molecular aspects were observed in Klf5knockout group, including enhanced activity of Akt/Mtor/S6axis and Erk-MAPK signaling, decreased p15, reversal of basal/luminal ratio, loss of smooth muscle layer, and significantly increased intraepithelial blood vessels.Finally, we knocked out both Klf5and Nkx3-1in mouse prostates to determine whether they have any additive or synergistic effects on prostatic tumorigenesis. However, we found that mice with the knockout of both genes displayed histopathologic and molecular features that were similar to those caused by the deletion of Nkx3-1alone.These results suggest that KLF5plays an important role in the proliferation and differentiation of prostatic epithelial cells, yet loss of KLF5alone is insufficient to induce malignant transformation. Loss of Klf5and Pten synergistically cooperate to arise and promote the prostate carcinogenesis, while deletions of Klf5and Nkx3-1do not have an additive effect. These results also validate the in vivo tumor suppressor function of Klf5in prostate.