Induction of integrin ß3 by sustained ERK activity promotes the invasiveness of TGFß-induced mesenchymal tumor cells.

The emerging roles of integrin ß3 in the epithelial-mesenchymal transition (EMT) and drug resistance underline its significance in cancer metastasis and recurrence. However, the molecular mechanism underlying the distinctive expression of integrin ß3 is less understood. In the present report, we demonstrated that repetitive exposure to transforming growth factor ß (TGFß), a potent inducer of the EMT, significantly increased the expression of integrin ß3 in A549 lung cancer cells with distinct mesenchymal properties, such as actin filament reorganization and invasiveness. Notably, integrin ß3 expression was associated to cancer cell invasion and migration, and was determined not by Smad4-dependent pathways but by sustained ERK1/2 activity in the mesenchymal cancer cells. These data suggest that ERK1/2 plays an important role in mediating non-canonical TGFß signal pathways for integrin ß3 expression. Therefore, the targeting of the MEK/ERK activity seems to be a promising therapeutic approach to suppressing EMT-associated cancer progression that potentially occurs in TGFß-enriched microenvironments, which would lead to the suppression of the metastatic potential of integrin ß3-positive cancer cells.

Chronic TGFß stimulation promotes the metastatic potential of lung cancer cells by Snail protein stabilization through integrin ß3-Akt-GSK3ß signaling.

Chronic exposure to TGFß, a frequent occurrence for tumor cells in the tumor microenvironment, confers more aggressive phenotypes on cancer cells by promoting their invasion and migration while at the same time increasing their resistance to the growth-inhibitory effect of TGFß. In this study, a transdifferentiated (TD) A549 cell model, established by chronically exposing A549 cells to TGFß, showed highly invasive phenotypes in conjunction with attenuation of Smad-dependent signaling. We show that Snail protein, the mRNA expression of which strongly correlates with a poor prognosis in lung cancer patients, was highly stable in TD cells after TGFß stimulation. The increased protein stability of Snail in TD cells correlated with elevated inhibitory phosphorylation of GSK3ß, resulting from the high Akt activity. Notably, integrin ß3, whose expression was markedly increased upon sustained exposure to TGFß, was responsible for the high Akt activity as well as the increased Snail protein stability in TD cells. Consistently, clinical database analysis on lung cancer patients revealed a negative correlation between overall survival and integrin ß3 mRNA levels. Therefore, we suggest that the integrin ß3-Akt-GSK3ß signaling axis plays an important role in non-canonical TGFß signaling, determining the invasive properties of tumor cells chronically exposed to TGFß.

GalNAc-T14 promotes metastasis through Wnt dependent HOXB9 expression in lung adenocarcinoma.

While metastasis, the main cause of lung cancer-related death, has been extensively studied, the underlying molecular mechanism remains unclear. A previous clinicogenomic study revealed that expression of N-acetylgalactosaminyltransferase (GalNAc-T14), is highly inversely correlated with recurrence-free survival in those with non-small cell lung cancer (NSCLC). However, the underlying molecular mechanism(s) has not been determined. Here, we showed that GalNAc-T14 expression was positively associated with the invasive phenotype. Microarray and biochemical analyses revealed that HOXB9, the expression of which was increased in a GalNAc-T14-dependent manner, played an important role in metastasis. GalNAc-T14 increased the sensitivity of the WNT response and increased the stability of the ß-catenin protein, leading to induced expression of HOXB9 and acquisition of an invasive phenotype. Pharmacological inhibition of ß-catenin in GalNAc-T14-expressing cancer cells suppressed HOXB9 expression and invasion. A meta-analysis of clinical genomics data revealed that expression of GalNAc-T14 or HOXB9 was strongly correlated with reduced recurrence-free survival and increased hazard risk, suggesting that targeting ß-catenin within the GalNAc-T14/WNT/HOXB9 axis may be a novel therapeutic approach to inhibit metastasis in NSCLC.

SIRT1 is required for oncogenic transformation of neural stem cells and for the survival of "cancer cells with neural stemness" in a p53-dependent manner.

BACKGROUND: Cancer stemness, observed in several types of glioma stem cells (GSCs), has been demonstrated to be an important barrier for efficient cancer therapy. We have previously reported that cancerous neural stem cells (F3.Ras.CNSCs), derived from immortalized human neural stem cells by a single oncogenic stimulation, form glial tumors in vivo. METHOD: We searched for a commonly expressed stress modulator in both F3.Ras.CNSCs and GSCs and identified silent mating type information regulation 2, homolog (SIRT1) as a key factor in maintaining cancer stemness. RESULT: We demonstrate that the expression of SIRT1, expressed in "cancer cells with neural stemness," is critical not only for the maintenance of stem cells, but also for oncogenic transformation. Interestingly, SIRT1 is essential for the survival and tumorigenicity of F3.Ras.CNSCs and GSCs but not for the U87 glioma cell line. CONCLUSION: These results indicate that expression of SIRT1 in cancer cells with neural stemness plays an important role in suppressing p53-dependent tumor surveillance, the abrogation of which may be responsible not only for inducing oncogenic transformation but also for retaining the neural cancer stemness of the cells, suggesting that SIRT1 may be a putative therapeutic target in GSCs.

Off-target response of a Wip1 chemical inhibitor in skin keratinocytes.

BACKGROUND: The wild type p53 inducible phosphatase (Wip1) plays an important role in modulating not only stress responses by various environmental stresses, but when overexpressed it also impairs the intrinsic tumor surveillance networks that are frequently found in a number of cancers including skin cancers. As a result, using a pharmacological inhibitor of Wip1 has been suggested to be a novel chemotherapeutic approach to recover the innate tumor surveillance in a variety of cancers. OBJECTIVE: We studied the effect of a pharmacological inhibitor of Wip1 in skin keratinocytes, under a ultra-violet (UV) stress condition. METHODS: A human keratinocyte cell line or human epidermal keratinocytes were exposed to UV, with or without the sole commercially available chemical inhibitor of Wip1, CCT007093; subsequently, we determined the diverse stress responses, including apoptosis and the activation of stress signaling. RESULTS: We demonstrate that the Wip1 inhibitor unexpectedly attenuated the UV-mediated apoptotic response in skin keratinocytes, as a consequence of attenuated JNK activation and reduced H2AX phosphorylation in both, skin keratinocytes and a Wip1-null cell model. On the other hand, the loss of Wip1 expression, either by knockout or knockdown in mice or human keratinocytes respectively, promoted apoptosis and potentiated H2AX phosphorylation following UV treatment. Of note, CCT007093 treatment appeared to promote apoptosis in breast cancer cells and skin transformed keratinocytes that ectopically expressed Wip1, demonstrating that the effect of CCT007093 differs based on the level of Wip1 expression. CONCLUSION: Thus, our studies suggest that the development of a more potent and specific Wip1 inhibitor is necessary to achieve the desired chemotherapeutic potential and to avoid off-target effects.