KLF4 is a tumor suppressor in B-cell non-Hodgkin lymphoma and in classic Hodgkin lymphoma

Loss of nuclear expression of Krüppel-like factor 4 is associated with poor prognosis in patients with oral cancer

Krüppel-like factor 4 is not only involved in cell proliferation but also affects cell differentiation and extracellular matrix production via positive and negative regulation of the expression of a wide range of genes. To our knowledge, little information is available regarding the role of Krüppel-like factor 4 in oral squamous cell carcinoma. In this study, we investigated the associations between Krüppel-like factor 4 expression and clinical parameters of oral cancer using immunohistochemical assays in 215 surgical specimens. Compared with positive nuclear Krüppel-like factor 4 expression, we observed that negative nuclear Krüppel-like factor 4 expression was significantly associated with an advanced cancer stage (P = .046), a high tumor recurrence rate (P = .009), and a worse 3-year survival rate in patients with oral cancer (P = .046). Nuclear expression of Krüppel-like factor 4 was shown to have an inverse relationship with Ki67 expression (P = .046). Patients with negative nuclear expression of Krüppel-like factor 4 had significantly worse overall survival rates as defined by the log-rank test (P = .014). Patients with oral cancer with negative nuclear Krüppel-like factor 4 expression in tumor cells had poor prognoses and a 2.5-fold higher death risk. Compared with disease stage (P = .025), negative nuclear Krüppel-like factor 4 expression (P = .006) was an independent prognostic factor. Our results revealed that the loss of nuclear expression of Krüppel-like factor 4 is significantly associated with aggressive clinical manifestations and might be an adverse survival factor.

Krüppel-like factor 4 inhibits tumorigenic progression and metastasis in a mouse model of breast cancer

Krüppel-like factor 4 (KLF4) is a zinc finger transcription factor that functions as an oncogene or tumor suppressor in a highly tissue-specific cell-dependent manner. However, its precise role in breast cancer and metastasis remains unclear. Here, we show that transient adenoviral expression of KLF4 in the 4T1 orthotopic mammary cancer model significantly attenuated primary tumor growth as well as micrometastases to the lungs and liver. These results can be attributed, in part, to decreased proliferation and increased apoptosis. Further supporting a tumor-suppressive role for KLF4 in the breast, we found that KLF4 expression is lost in a mouse model of HER2/NEU/ERBB2-positive breast cancer. To determine whether enforced KLF4 expression could alter tumor latency in these mice, we used a doxycycline-inducible expression model in the context of the MMTV-Neu transgene. Surprisingly, tumors that developed in this model also lost KLF4 expression, suggesting negative selection for sustained expression. We have previously reported that KLF4 inhibits epithelial-to-mesenchymal transition (EMT), a preliminary step in metastatic progression. Overexpression of KLF4 in 4T1 cells led to a significant reduction in the expression of Snail, a key mediator of EMT and metastasis. Conversely, KLF4 silencing increased Snail expression in the nontransformed MCF-10A cell line. Collectively, these data demonstrate the first functional, in vivo evidence for KLF4 as a tumor suppressor in breast cancer cells. Furthermore, our findings suggest an inhibitory role for KLF4 during breast cancer metastases that functions, in part, through repression of Snail.

Krüppel-like transcription factors in the nervous system: novel players in neurite outgrowth and axon regeneration

The Krüppel-like family of transcription factors (KLFs) have been widely studied in proliferating cells, though very little is known about their role in post-mitotic cells, such as neurons. We have recently found that the KLFs play a role in regulating intrinsic axon growth ability in retinal ganglion cells (RGCs), a type of central nervous system (CNS) neuron. Previous KLF studies in other cell types suggest that there may be cell-type specific KLF expression patterns, and that their relative expression allows them to compete for binding sites, or to act redundantly to compensate for another's function. With at least 15 of 17 KLF family members expressed in neurons, it will be important for us to determine how this complex family functions to regulate the intricate gene programs of axon growth and regeneration. By further characterizing the mechanisms of the KLF family in the nervous system, we may better understand how they regulate neurite growth and axon regeneration.

MicroRNA-373, a new regulator of protein phosphatase 6, functions as an oncogene in hepatocellular carcinoma

MicroRNAs are a class of small noncoding RNAs that function as key regulators of gene expression at the post-transcriptional level. Recently, microRNA-373 (miR-373) has been found to function as an oncogene in testicular germ cell tumors. In our study, we found that miR-373 is upregulated in human hepatocellular carcinoma (HCC) tissues as compared with adjacent normal tissues, and promotes the proliferation of the HCC cell lines HepG2 and QGY-7703 by regulating the transition between G(1)-phase and S-phase. The gene encoding the protein phosphatase 6 catalytic subunit (PPP6C ), a negative cell cycle regulator, was identified as a direct target gene of miR-373 by use of a fluorescent reporter assay. The mRNA and protein levels of PPP6C were both inversely correlated with the miR-373 expression level. Overexpression of PPP6C abolished the regulation of cell cycle and cell growth exercised by miR-373 in HepG2 cells. These results indicate that miR-373 plays an important role in the pathogenesis of HCC, and may be a new biomarker in HCC. Our results demonstrate that miR-373 can regulate cell cycle progression by targeting PPP6C transcripts and promotes the growth activity of HCC cells in vitro. The downregulation of PPP6C by miR-373 may explain why the expression of miR-373 can promote HCC cell proliferation.

Regulation of Krüppel-like factor 4 by the anaphase promoting complex pathway is involved in TGF-beta signaling

Krüppel-like factor 4 (KLF4), a zinc finger-containing transcriptional factor, regulates a variety of biological processes, including cell proliferation, differentiation, apoptosis, and stem cell reprogramming. Post-translational modifications of KLF4, including phosphorylation, acetylation, and sumoylation, regulate its transcriptional activity. Most recent studies also demonstrate that KLF4 is targeted for ubiquitin-dependent proteolysis during cell cycle progression. However, the underlying mechanism remains largely unknown. In this study, we demonstrated that KLF4 is profoundly degraded in response to TGF-β signaling. We have identified the Cdh1-anaphase promoting complex as a putative E3 ligase that governs TGF-β-induced KLF4 degradation. The TGF-β-induced KLF4 degradation is mediated by the destruction box on the KLF4. Either depletion of Cdh1 by RNA interference or stabilization of KLF4 by disruption of its destruction box significantly attenuates TGF-β-induced ubiquitylation and degradation. In addition, depletion of Cdh1 or stabilization of KLF4 antagonizes TGF-β-induced activation of transcription. Determining the role of KLF4 proteolysis in response to TGF-β signaling has opened a new perspective to understand the TGF-β signaling pathway.