Changsheng Xing

Atbf1 Regulates Pubertal Mammary Gland Development Likely by Inhibiting the Pro-Proliferative Function of Estrogen-ER Signaling

ATBF1 is a candidate tumor suppressor that interacts with estrogen receptor (ER) to inhibit the function of estrogen-ER signaling in gene regulation and cell proliferation control in human breast cancer cells. We therefore tested whether Atbf1 and its interaction with ER modulate the development of pubertal mammary gland, where estrogen is the predominant steroid hormone. In an in vitro model of cell differentiation, i.e., MCF10A cells cultured in Matrigel, ATBF1 expression was significantly increased, and knockdown of ATBF1 inhibited acinus formation. During mouse mammary gland development, Atbf1 was expressed at varying levels at different stages, with higher levels during puberty, lower during pregnancy, and the highest during lactation. Knockout of Atbf1 at the onset of puberty enhanced ductal elongation and bifurcation and promoted cell proliferation in both ducts and terminal end buds of pubertal mammary glands. Enhanced cell proliferation primarily occurred in ER-positive cells and was accompanied by increased expression of ER target genes. Furthermore, inactivation of Atbf1 reduced the expression of basal cell markers (CK5, CK14 and CD44) but not luminal cell markers. These findings indicate that Atbf1 plays a role in the development of pubertal mammary gland likely by modulating the function of estrogen-ER signaling in luminal cells and by modulating gene expression in basal cells.

Different Expression Patterns and Functions of Acetylated and Unacetylated Klf5 in the Proliferation and Differentiation of Prostatic Epithelial Cells

KLF5 is a basic transcription factor that regulates multiple biological processes. While it was identified as a putative tumor suppressor in prostate cancer, likely due to its function as an effector of TGF-β in the inhibition of cell proliferation, KLF5 is unacetylated and promotes cell proliferation in the absence of TGF-β. In this study, we evaluated the expression and function of KLF5 in prostatic epithelial homeostasis and tumorigenesis using mouse prostates and human prostate epithelial cells in 3-D culture. Histological and molecular analyses demonstrated that unacetylated-Klf5 was expressed in basal or undifferentiated cells, whereas acetylated-Klf5 was expressed primarily in luminal and/or differentiated cells. Androgen depletion via castration increased both the level of Klf5 expression and the number of Klf5-positive cells in the remaining prostate. Functionally, knockdown of KLF5 in the human RWPE-1 prostate cell line decreased the number of spheres formed in 3-D culture. In addition, knockout of Klf5 in prostate epithelial cells, mediated by probasin promoter-driven Cre expression, did not cause neoplasia but promoted cell proliferation and induced hyperplasia when one Klf5 allele was knocked out. Knockout of both Klf5 alleles however, caused apoptosis rather than cell proliferation in the epithelium. In castrated mice, knockout of Klf5 resulted in more severe shrinkage of the prostate. These results suggest that KLF5 plays a role in the proliferation and differentiation of prostatic epithelial cells, yet loss of KLF5 alone is insufficient to induce malignant transformation in epithelial cells.

Heterozygous deletion of Atbf1 by the Cre-loxP system in mice causes preweaning mortality

ATBF1 is a large nuclear protein that contains multiple zinc‐finger motifs and four homeodomains. In mammals, ATBF1 regulates differentiation, and its mutation and/or downregulation is involved in tumorigenesis in several organs. To gain more insight into the physiological functions of ATBF1, we generated and validated a conditional allele of mouse Atbf1 in which exons 7 and 8 were flanked by loxP sites (Atbf1flox). Germline deletion of a single Atbf1 allele was achieved by breeding to EIIa‐cre transgenic mice, and Atbf1 heterozygous mice displayed reduced body weight, preweaning mortality, increased cell proliferation, and attenuated cytokeratin 18 expression, indicating haploinsufficiency of Atbf1. Floxed Atbf1 mice will help us understand such biological processes as neuronal differentiation and tumorigenesis. genesis 1–9, 2012.

KLF5 inhibits angiogenesis in PTEN-deficient prostate cancer by attenuating AKT activation and subsequent HIF1α accumulation

BackgroundKLF5 is a basic transcriptional factor that regulates multiple physiopathological processes. Our recent study showed that deletion of Klf5 in mouse prostate promotes tumorigenesis initiated by the deletion of Pten. While molecular characterization of Klf5-null tumors suggested that angiogenesis was partially responsible for tumor promotion, the precise function and mechanism of KLF5 deletion in prostate tumor angiogenesis remain unclear.ResultsApplying histological staining to Pten-null mouse prostates, we observed that deletion of Klf5 significantly increased the number of microvessels, accompanied by the upregulation of multiple angiogenesis-related genes based on microarray analysis with MetaCore software. In human umbilical vein endothelial cells (HuVECs), tube formation and migration, both of which are indicators of angiogenic activities, were decreased by conditioned media from PC-3 and DU 145 human prostate cancer cells with KLF5 overexpression, but increased by media from cells with KLF5 knockdown. HIF1α, a key angiogenesis inducer, was upregulated by KLF5 loss at the protein but not the mRNA level in both mouse tissues and human cell lines, as determined by immunohistochemical staining, real-time RT-PCR and Western blotting. Consistently, KLF5 loss also upregulated VEGF and PDGF, two pro-angiogenic mediators of HIF1α function, as analyzed by immunohistochemical staining in mouse tissues and ELISA in conditioned media. Mechanistically, AKT activity, which caused the accumulation of HIF1α, was increased by KLF5 knockout or knockdown but decreased by KLF5 overexpression. PI3K/AKT inhibitors consistently abolished the effects of KLF5 knockdown on angiogenic activity, HIF1α accumulation, and VEGF and PDGF expression.ConclusionKLF5 loss enhances tumor angiogenesis by attenuating PI3K/AKT signaling and subsequent accumulation of HIF1α in PTEN deficient prostate tumors.

Deletion of Atbf1/Zfhx3 In Mouse Prostate Causes Neoplastic Lesions, Likely by Attenuation of Membrane and Secretory Proteins and Multiple Signaling Pathways

The ATBF1/ZFHX3 gene at 16q22 is the second most frequently mutated gene in human prostate cancer and has reduced expression or mislocalization in several types of human tumors. Nonetheless, the hypothesis that ATBF1 has a tumor suppressor function in prostate cancer has not been tested. In this study, we examined the role of ATBF1 in prostatic carcinogenesis by specifically deleting Atbf1 in mouse prostatic epithelial cells. We also examined the effect of Atbf1 deletion on gene expression and signaling pathways in mouse prostates. Histopathologic analyses showed that Atbf1 deficiency caused hyperplasia and mouse prostatic intraepithelial neoplasia (mPIN) primarily in the dorsal prostate but also in other lobes. Hemizygous deletion of Atbf1 also increased the development of hyperplasia and mPIN, indicating a haploinsufficiency of Atbf1. The mPIN lesions expressed luminal cell markers and harbored molecular changes similar to those in human PIN and prostate cancer, including weaker expression of basal cell marker cytokeratin 5 (Ck5), cell adhesion protein E-cadherin, and the smooth muscle layer marker Sma; elevated expression of the oncoproteins phospho-Erk1/2, phospho-Akt and Muc1; and aberrant protein glycosylation. Gene expression profiling revealed a large number of genes that were dysregulated by Atbf1 deletion, particularly those that encode for secretory and cell membrane proteins. The four signaling networks that were most affected by Atbf1 deletion included those centered on Erk1/2 and IGF1, Akt and FSH, NF-κB and progesterone and β-estradiol. These findings provide in vivo evidence that ATBF1 is a tumor suppressor in the prostate, suggest that loss of Atbf1 contributes to tumorigenesis by dysregulating membrane and secretory proteins and multiple signaling pathways, and provide a new animal model for prostate cancer.

Klf5 Deletion Promotes Pten Deletion–Initiated Luminal-Type Mouse Prostate Tumors through Multiple Oncogenic Signaling Pathways

Krüppel-like factor 5 (KLF5) regulates multiple biologic processes. Its function in tumorigenesis appears contradictory though, showing both tumor suppressor and tumor promoting activities. In this study, we examined whether and how Klf5 functions in prostatic tumorigenesis using mice with prostate-specific deletion of Klf5 and phosphatase and tensin homolog (Pten), both of which are frequently inactivated in human prostate cancer. Histologic analysis demonstrated that when one Pten allele was deleted, which causes mouse prostatic intraepithelial neoplasia (mPIN), Klf5 deletion accelerated the emergence and progression of mPIN. When both Pten alleles were deleted, which causes prostate cancer, Klf5 deletion promoted tumor growth, increased cell proliferation, and caused more severe morphologic and molecular alterations. Homozygous deletion of Klf5 was more effective than hemizygous deletion. Unexpectedly, while Pten deletion alone expanded basal cell population in a tumor as reported, Klf5 deletion in the Pten-null background clearly reduced basal cell population while expanding luminal cell population. Global gene expression profiling, pathway analysis, and experimental validation indicate that multiple mechanisms could mediate the tumor-promoting effect of Klf5 deletion, including the up-regulation of epidermal growth factor and its downstream signaling molecules AKT and ERK and the inactivation of the p15 cell cycle inhibitor. KLF5 also appears to cooperate with several transcription factors, including CREB1, Sp1, Myc, ER and AR, to regulate gene expression. These findings validate the tumor suppressor function of KLF5. They also yield a mouse model that shares two common genetic alterations with human prostate cancer—mutation/deletion of Pten and deletion of Klf5.

Additive Effect of Zfhx3/Atbf1 and Pten Deletion on Mouse Prostatic Tumorigenesis.

The phosphatase and tensin homolog (PTEN) and the zinc finger homeobox 3 (ZFHX3)/AT-motif binding factor 1 (ATBF1) genes have been established as tumor suppressor genes in prostate cancer by their frequent deletions and mutations in human prostate cancer and by the formation of mouse prostatic intraepithelial neoplasia (mPIN) or tumor by their deletions in mouse prostates. However, whether ZFHX3/ATBF1 deletion together with PTEN deletion facilitates prostatic tumorigenesis is unknown. In this study, we simultaneously deleted both genes in mouse prostatic epithelia and performed histological and molecular analyses. While deletion of one Pten allele alone caused low-grade (LG) mPIN as previously reported, concurrent deletion of Zfhx3/Atbf1 promoted the progression to high-grade (HG) mPIN or early carcinoma. Zfhx3/Atbf1 and Pten deletions together increased cell proliferation, disrupted the smooth muscle layer between epithelium and stroma, and increased the number of apoptotic cells. Deletion of both genes also accelerated the activation of Akt and Erk1/2 oncoproteins. These results suggest an additive effect of ZFHX3/ATBF1 and PTEN deletions on the development and progression of prostate neoplasia.

Lack of an Additive Effect between the Deletions of Klf5 and Nkx3-1 in Mouse Prostatic Tumorigenesis

Prostate cancer is one of the most common malignancies and a leading cause of cancer death in industrialized countries. The development and progression of prostate cancer are driven by a series of genetic and epigenetic events including gene amplification that activates oncogenes and chromosomal deletion that inactivates tumor suppressor genes. Whereas gene amplification occurs in human prostate cancer, gene deletion is more common, and a large number of chromosomal regions have been identified to have frequent deletion in prostate cancer, suggesting that tumor suppressor inactivation is more common than oncogene activation in prostatic carcinogenesis (Knuutila et al., 1998, 1999; Dong, 2001). Among the most frequently deleted chromosomal regions in prostate cancer, target genes such as NKX3-1 from 8p21, PTEN from 10q23 and ATBF1 from 16q22 have been identified by different approaches (He et al., 1997; Li et al., 1997; Sun et al., 2005), and deletion of these genes in mouse prostates has been demonstrated to induce and/or promote prostatic carcinogenesis. For example, knockout of Nkx3-1 in mice induces hyperplasia and dysplasia (Bhatia-Gaur et al., 1999; Abdulkadir et al., 2002) and promotes prostatic tumorigenesis (Abate-Shen et al., 2003), while knockout of Pten alone causes prostatic neoplasia (Wang et al., 2003). Therefore, gene deletion plays a causal role in prostatic carcinogenesis (Dong, 2001).

Abstract LB-23: Ras signaling interrupts TGF-beta-induced KLF5 acetylation to alter the KLF5-Smads transcriptional assembly in epithelial cells

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL β (TGF-β) suppresses early stage tumorigenesis but promotes late stage tumor progression. While also presenting dual roles in tumorigenesis, KLF5 in the acetylated form is essential for TGF-β to properly regulate gene transcription in the inhibition of cell proliferation. The Ras oncogenic signaling not only converts TGF-β from a tumor suppressor to a tumor promoter but also uses KLF5 as a functional effector. One intriguing question is whether and how Ras signaling uses the KLF5 transcription factor to modulate TGF-β function. In this study, we addressed this question by examining whether and how Ras signaling alters TGF-β-induced KLF5 acetylation and the assembly of the p300-KLF5-Smads transcriptional complex in gene regulation. We found that Ras inhibited TGF-β-induced KLF5 acetylation and interfered with TGF-β in p15 induction and Myc repression. In addition, TGF-β-induced Smad3 phosphorylation at the C-terminal region was necessary for TGF-β to induce KLF5 acetylation, and Ras interrupted this phosphorylation. Ras signaling further interrupted the interactions among p300, KLF5 and Smad4, as well as the binding of the p300-KLF5-Smads complex onto the TGF-β-responsive promoter elements for both p15 and Myc. Without TGF-β, however, Ras signaling increased KLF5 acetylation, enhanced the p300-KLF5 interaction, and promoted the binding of the KLF5 transcriptional complex onto the TGF-β-responsive promoter elements. These findings suggest that KLF5 mediates the crosstalk between TGF-β and Ras signaling, and that suppression of TGF-β-induced KLF5 acetylation by Ras signaling alters TGF-β-induced assembly of p300-KLF5-Smads complex onto gene promoters, thus switching the function of TGF-β in gene regulation. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-23. doi:1538-7445.AM2012-LB-23

Abstract 1386: KLF5 inhibits angiogenesis in PTEN-deficient prostate cancer by attenuating AKT activation and subsequent HIF1α accumulation

Background: KLF5 is a basic transcriptional factor that regulates multiple physiopathological processes. Our recent study showed that deletion of Klf5 in mouse prostates promotes tumorigenesis initiated by the deletion of Pten. While molecular characterization of Klf5-null tumors suggested that angiogenesis was partially responsible for tumor promotion, the precise function and mechanism of KLF5 deletion in prostate tumor angiogenesis remain unclear. Results: Using histological staining of Pten-null mouse prostates, we observed that deletion of Klf5 significantly increased the number of microvessels, which was accompanied by the upregulation of multiple angiogenesis-related genes based on microarray analysis with MetaCore software. In human umbilical vein endothelial cells (HuVECs), tube formation and migration, both of which are indicators of angiogenic activities, were decreased by conditioned media from PC-3 and DU 145 human prostate cancer cells with KLF5 overexpression, but increased by media from cells with KLF5 knockdown. HIF1α, a key angiogenesis inducer, was upregulated by KLF5 loss at the protein but not the mRNA level in both mouse tissues and human cell lines, as examined by immunohistochemical staining, real-time RT-PCR and Western blotting. Consistently, KLF5 loss also upregulated VEGF and PDGF, two pro-angiogenic mediators of HIF1α function, as analyzed by immunohistochemical staining in mouse tissues and ELISA in conditioned media. Mechanistically, AKT activity, which caused the accumulation of HIF1α, was increased by KLF5 knockout or knockdown but decreased by KLF5 overexpression. Consistently, PI3K/AKT inhibitors abolished the effects of KLF5 knockdown on angiogenic activity, HIF1α accumulation, and VEGF and PDGF expression. Conclusion: KLF5 loss enhances tumor angiogenesis by attenuating PI3K/AKT signaling and subsequent accumulation of HIF1α in PTEN deficient prostate tumors. Citation Format: Xinpei Ci, Changsheng Xing, Baotong Zhang, Zhiqian Zhang, Jenny Jianping Ni, Wei Zhou, Jin-Tang Dong. KLF5 inhibits angiogenesis in PTEN-deficient prostate cancer by attenuating AKT activation and subsequent HIF1α accumulation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1386. doi:10.1158/1538-7445.AM2015-1386