Wnt inhibitory factor 1 is epigenetically silenced in human osteosarcoma, and targeted disruption accelerates osteosarcomagenesis in mice

Abstract

Wnt signaling increases bone mass by stimulating osteoblast lineage commitment and expansion and forms the basis for novel anabolic therapeutic strategies being developed for osteoporosis. These strategies include derepression of Wnt signaling by targeting secreted Wnt pathway antagonists, such as sclerostin. However, such therapies are associated with safety concerns regarding an increased risk of osteosarcoma, the most common primary malignancy of bone. Here, we analyzed 5 human osteosarcoma cell lines in a high-throughput screen for epigenetically silenced tumor suppressor genes and identified Wnt inhibitory factor 1 (WIF1), which encodes an endogenous secreted Wnt pathway antagonist, as a candidate tumor suppressor gene. In vitro, WIF1 suppressed β-catenin levels in human osteosarcoma cell lines, induced differentiation of human and mouse primary osteoblasts, and suppressed the growth of mouse and human osteosarcoma cell lines. Wif1 was highly expressed in the developing and mature mouse skeleton, and, although it was dispensable for normal development, targeted deletion of mouse Wif1 accelerated development of radiation-induced osteosarcomas in vivo. In primary human osteosarcomas, silencing of WIF1 by promoter hypermethylation was associated with loss of differentiation, increased β-catenin levels, and increased proliferation. These data lead us to suggest that derepression of Wnt signaling by targeting secreted Wnt antagonists in osteoblasts may increase susceptibility to osteosarcoma.

Wnt inhibitory factor 1 induces apoptosis and inhibits cervical cancer growth, invasion and angiogenesis in vivo

“…These results are consistent with the in vitro observations that WIF1 overexpression does not interfere with normal cell growth of primary osteoblasts (Kansara et al, 2009) and HEK293 cells (data not published). Moreover, the use of peritumoral injection has the selective advantage of treating tumors with WIF1 at the tumor site, while avoiding the potential side effects at undesired target tissues often associated with systemic therapeutic strategies.…”

“…This inhibition of cell proliferation is consistent with the in vitro inhibition of cell growth by WIF1 as previously shown for other cancer cell lines (Ai et al, 2006;Kim et al, 2007;Kansara et al, 2009;Kawakami et al, 2009;Tang et al, 2009). However, in previous studies, WIF1 overexpression was shown to induce G 1 arrest in HPVimmortalized osteoblasts and osteosarcoma cell lines containing null or wild-type p53 (Kansara et al, 2009), as well as in bladder cancer cell lines containing mutant p53 (Tang et al, 2009). In contrast, our data show that in cervical cancer cells, which express very low levels of wild-type p53, WIF1 re-expression led to a significant increase in p53 expression, and induced cell-cycle arrest at G 2 /M and extensive apoptosis.…”

“…Re-expression of WIF1 resulted in a significant reduction in the total number of viable cells at all time points (Figure 3a), indicating the potent growth-inhibitory effects of WIF1. In bladder carcinoma and osteosarcoma cell lines, WIF1 has been reported to induce G 1 arrest and growth inhibition (Kansara et al, 2009;Tang et al, 2009). However, consistent with the G 2 /M arrest observed in cervical cancer cells after DAC treatment, we observed a significant increase in the G 2 /M phase of the cell cycle in WIF1-transfected cells (Figure 3b), suggesting a cellspecific role for WIF1.…”

Targeting Wnts at the Source—New Mechanisms, New Biomarkers, New Drugs

“…Epigenetic silencing of sFRP promoters by hypermethylation is seen in colorectal and breast cancers (66,69). Wnt inhibitory factor-1, another secreted Wnt inhibitor, is silenced in several tumor types (73)(74)(75). Profiling the expression of Wnt antagonists or epigenetic marks associated with their silencing, while challenging in clinical practice, could be useful to predict sensitivity of tumors to upstream Wnt inhibitors.…”

Osteosarcoma

“…(24)(25)(26)(27)(28) It has been noted that Wnt inhibitory factor 1 is epigenetically silence in human osteosarcomas, with targeted disruption in mice accelerating osteosarcoma development. (29) With the existing available data, it appears likely that the Wnt signaling pathway has an important role in osteosarcoma, but it is unclear whether up-or downregulation promotes its formation and malignant behavior.…”