Frizzled-4 is required for normal bone acquisition despite compensation by Frizzled-8

The activation of the Wnt/β-catenin signaling pathway is critical for skeletal development but surprisingly little is known about the requirements for the specific frizzled (Fzd) receptors that recognize Wnt ligands. To define the contributions of individual Fzd proteins to osteoblast function, we profiled the expression of all 10 mammalian receptors during calvarial osteoblast differentiation. Expression of Fzd4 was highly upregulated during in vitro differentiation and therefore targeted for further study. Mice lacking Fzd4 in mature osteoblasts had normal cortical bone structure but reduced cortical tissue mineral density and also exhibited an impairment in the femoral trabecular bone acquisition that was secondary to a defect in the mineralization process. Consistent with this observation, matrix mineralization, markers of osteoblastic differentiation, and the ability of Wnt3a to stimulate the accumulation of β-catenin were reduced in cultures of calvarial osteoblasts deficient for Fzd4. Interestingly, Fzd4-deficient osteoblasts exhibited an increase in the expression of Fzd8 both in vitro and in vivo, which suggests that the two receptors may exhibit overlapping functions. Indeed, ablating a single Fzd8 allele in osteoblast-specific Fzd4 mutants produced a more severe effect on bone acquisition. Taken together, our data indicate that Fzd4 is required for normal bone development and mineralization despite compensation from Fzd8.

Long noncoding RNA AK126698 inhibits proliferation and migration of non-small cell lung cancer cells by targeting Frizzled-8 and suppressing Wnt/β-catenin signaling pathway

Background

Recent studies indicate that long noncoding RNAs (lncRNAs) play a key role in the control of cellular processes such as proliferation, metastasis, and differentiation. The lncRNA dysregulation has been identified in all types of cancer. We previously found that lncRNA AK126698 suppresses cisplatin resistance in A549 cells through the Wnt/β-catenin signaling pathway. However, the clinical significance of lncRNA AK126698 and the molecular mechanisms through which it regulates cancer cell proliferation and migration are largely unknown.

Methods

We examined the expression of lncRNA AK126698 in 56 non-small cell lung cancer (NSCLC) tissue samples and three NSCLC cell lines using quantitative real-time polymerase chain reaction. Gain and loss of function approaches were used to evaluate the biological function of AK126698 in NSCLC cells. The effects of lncRNA AK126698 on cell proliferation were investigated using cell counting kit-8 and 5-ethynyl-2′-deoxyuridine assays, and apoptosis was measured by flow cytometry. Protein levels of AK126698 targets were evaluated by Western blotting.

Results

Our results showed that lncRNA AK126698 was significantly downregulated in NSCLC tissues, compared with paired adjacent nontumor tissue samples. Furthermore, lower AK126698 expression was associated with larger tumor size and advanced tumor stage. Ectopic AK126698 expression inhibited cell proliferation and migration and induced apoptosis. Conversely, decreased AK126698 expression promoted cell proliferation and migration and inhibited cell apoptosis. Importantly, we demonstrated that Frizzled-8, a receptor of Wnt/β-catenin pathway, was a target of AK126698. Furthermore, AK126698 could inhibit the activation of Wnt/β-catenin pathway, which was demonstrated by measuring the expression levels of Axin1, β-catenin, c-myc, cyclin D1, and E-cadherin.

Conclusion

It was found in the study that lncRNA AK126698 inhibits the proliferation and migration of NSCLC cells by targeting Frizzled-8 to suppress the Wnt/β-catenin signaling pathway. It may provide a new target for therapeutic intervention in NSCLC.