The FOXO transcription factors control proliferation and apoptosis in different cell types. Their activity is regulated by posttranslational modifications, mainly by the PI3K-PKB pathway, which controls nuclear export and degradation. We show that FOXO1 is highly expressed in normal germinal center B cells as well as in non-Hodgkin lymphomas, including follicular lymphoma, diffuse large B-cell lymphoma, mucosa-associated lymphoid tissue non-Hodgkin lymphoma, B-cell chronic lymphocytic leukemia, and mantle cell lymphoma. In contrast, in 31 of 32 classical Hodgkin lymphoma (cHL) cases, Hodgkin and Reed-Sternberg cells were FOXO1 negative. Neoplastic cells of nodular lymphocyte-predominant Hodgkin lymphoma were negative in 14 of 20 cases. FOXO1 was down-regulated in cHL cell lines, whereas it was expressed in non-Hodgkin lymphoma cell lines at levels comparable with normal B cells. Ectopic expression of a constitutively active FOXO1 induced apoptosis in cHL cell lines and blocked proliferation, accompanied with cell-cycle arrest in the G₀/G₁ phase. We found that, in cHL cell lines, FOXO1 is inactivated by multiple mechanisms, including constitutive activation of AKT/PKB and MAPK/ERK kinases and up-regulation of microRNAs miR-96, miR-182, and miR-183. These results suggest that FOXO1 repression contributes to cHL lymphomagenesis.

The transcription factor KLF4 may act both as an oncogene and a tumor suppressor in a tissue-depending manner. In T- and pre-B-cell lymphoma, KLF4 was found to act as tumor suppressor. We found the KLF4 promoter methylated in B-cell lymphoma cell lines and in primary cases of B-cell lymphomas, namely, follicular lymphoma, diffuse large B-cell lymphoma, Burkitt lymphoma, and in classic Hodgkin lymphoma (cHL) cases. Promoter hypermethylation was associated with silencing of KLF4 expression. Conditional overexpression of KLF4 in Burkitt lymphoma cell lines moderately retarded proliferation, via cell-cycle arrest in G0/G1. In the cHL cell lines, KLF4 induced massive cell death that could partially be inhibited with Z-VAD.fmk. A quantitative reverse-transcribed polymerase chain reaction array revealed KLF4 target genes, including the proapoptotic gene BAK1. Using an shRNA-mediated knock-down approach, we found that BAK1 is largely responsible for KLF4-induced apoptosis. In addition, we found that KLF4 negatively regulates CXCL10, CD86, and MSC/ABF-1 genes. These genes are specifically up-regulated in HRS cells of cHL and known to be involved in establishing the cHL phenotype. We conclude that epigenetic silencing of KLF4 in B-cell lymphomas and particularly in cHL may favor lymphoma survival by loosening cell-cycle control and protecting from apoptosis.

Epoxyeicosatrienoic acids (EETs) are products of arachidonic acid metabolism catalyzed by cytochrome P450 epoxygenases. These small molecules are autocrine and paracrine lipid mediators with important roles in inflammation, cardiovascular function, and angiogenesis. Recent evidence has highlighted EETs as potent promoters of organ regeneration and malignant metastasis. We speculated that EETs might impact osteoclastogenesis and bone loss. Using both in vitro and in vivo studies, we observed that EETs significantly attenuated bone loss and inhibited osteoclast formation and activity, which were associated with a decreased receptor activator of NF‐κB ligand (RANKL): osteoprotegerin ratio and serum levels of TNF‐α and IL‐1β. At the molecular level, EETs abrogated RANKL‐induced activation of NF‐κB, activator protein‐1 (AP‐1), and MAPKs, including ERK and JNK, but not p38, during osteoclast formation. EETs also prevented the production of reactive oxygen species (ROS) following RANKL stimulation. As a result, EETs suppressed osteoclast‐specific gene expression, including tartrate resistant acid phosphatase (TRAP), cathepsin K (CK), matrix metalloproteinase (MMP)‐9, and receptor activator of NF‐κB (RANK). In conclusion, our findings demonstrate that EETs inhibit osteoclastogenesis through modulation of multiple pathways both upstream and downstream of RANKL signaling. The administration or stabilized endogenous levels of EETs could represent a novel therapeutic strategy for osteoclast‐related disorders, such as rheumatoid arthritis and postmenopausal osteoporosis.—Guan, H., Zhao. L., Cao, H., Chen, A., Xiao, J., Epoxyeicosanoids suppress osteoclastogenesis and prevent ovariectomy‐induced bone loss. FASEB J. 29, 1092–1101 (2015). www.fasebj.org

Recent advances have highlighted profound roles of FOXO transcription factors, especially FOXO1, in bone development and remodeling. The regulation of bone development by FOXOs seems to be stage-specific or context dependent. FOXOs promote maintenance and differentiation of early progenitors of the osteoblast lineage and repress proliferation of committed osteoblast precursors; FOXO1 is vital for osteocyte survival. Considering the versatile roles played by FOXOs in bone development and tumorigenesis, it is plausible that FOXO1, the main FOXO in bone with a non-redundant role, might have influence on osteosarcoma (OS) oncogenesis. Indeed, recent results have implicated that FOXO1 has a tumor-suppressing role in OS. In the present study, we found thatFOXO1expression was generally low or absent in OS, with a minority of cases having moderate expression. Whole-genome sequencing (WGS) revealed that theFOXO1locus was frequently involved in copy number variation and loss of heterozygosity in OS, indicating that chromosomal aberrations might be partially responsible for the heterogeneity inFOXO1expression. FOXO1 activation in OS cell lines inhibited cancer cell survival, which can be attributed to modulation of target genes, includingBIMand repressed Wnt/β-catenin signaling. FOXO1 inhibition promoted cell proliferation, enhanced colony formation and attenuated osteogenic differentiation of OS cell lines. To conclude, our results proved FOXO1 as a tumor suppressor in OS at least partially by suppression of the Wnt/β-catenin pathway.