Association of cytoplasmic p27 expression with an unfavorable response to cisplatin-based chemotherapy and poor outcomes in non-small cell lung cancer

The clinicopathological and prognostic significance of P27kip in hepatocellular carcinoma patients: A systemic review and meta-analysis

OBJECTIVES

P27^kip is a cyclin-dependent kinase inhibitor that has gained importance as a biomarker in human malignant tumors. However, the potential role of P27^kip in hepatocellular carcinoma remains unclear. The aim of this meta-analysis was to explore whether P27^kip acts as prognostic and clinicopathological roles in hepatocellular carcinoma patients.

METHODS/MATERIALS

An electronic search based on three databases, PubMed, Embase, and Web of Science, was performed to select a sufficient number of studies. Pooled hazard ratio (HR) and odds ratio (OR) were used as estimates to investigate the association among P27^kip expression, prognosis and clinicopathological features.

RESULTS

In total, we identified 18 studies with 1774 hepatocellular carcinoma patients. The result derived from four studies revealed a significant positive association between lower P27^kip levels and shorter overall survival (HR = 0.550, 95% CI: 0.464-0.652, P < 0001) and disease-free survival (HR = 0.420, 95% CI: 0.308-0.571, P < 0.0001). Analyses of the clinicopathological features and P27^kip expression also showed that a positive rate of P27^kip was significantly lower in a larger sized tumor (OR = 0.538, 95% CI: 0.315-0.919, P = 0.023). The results also revealed that lower P27^kip levels were correlated with poorer differentiation (0.416, 95% CI: 0.178-0.971, P = 0.043). Additionally, the pooled OR of 0.389 also presented a significant correlation between P27^kip underexpression and the metastasis of HCCs (95% CI: 0.155-0.975, P = 0.044).

CONCLUSIONS

This analysis suggests a strong association among P27^kip underexpression, poorer prognosis and aggressive progression of hepatocellular carcinoma in patients. P27^kip may be a tumor suppressor for predicting the progression and survival outcome in patients with hepatocellular carcinomas.

IRF8 induces senescence of lung cancer cells to exert its tumor suppressive function

Lung cancer is the leading cause of cancer-related deaths worldwide. However, tumor suppressor genes remain to be systemically determined for lung cancer. Here we report interferon regulatory factor 8 (IRF8), a member of the IRF family of transcription factors, as a potent lung tumor suppressor gene. Expression of IRF8 is frequently diminished in lung tumoral tissues and is associated with prognosis of non-small cell lung cancer (NSCLC) patients. Ectopic expression of IRF8 suppresses the NSCLC cells proliferation in vitro and tumorigenic potential in vivo. More importantly, forced expression of IRF8 through infection of recombinant virus inhibits lung tumorigenesis in genetically engineered mouse model (GEMM). Mechanistically, IRF8 inhibits AKT signaling and promotes accumulation of P27 protein, which results in senescence of lung cancer cells. Ectopic expression of IRF8 in tumor cells leads to regression of lung cancer tumor nodules in a xenograft tumor model. Our data, therefore, solidly shows IRF8 to be a lung cancer suppressor gene and may denote an opportunity for therapeutic intervention of NSCLC.

p27Kip1 - p(RhoB)lematic in lung cancer

Lung cancer is the leading cause of cancer mortality worldwide, with adenocarcinomas of the non‐small cell lung carcinoma (NSCLC) subtype accounting for the majority of cases. Therefore, an urgent need exists for a more detailed dissection of the molecular events driving NSCLC development and the identification of clinically relevant biomarkers. Even though originally identified as a tumour suppressor, recent studies associate the cytoplasmically (mis)localised CDK inhibitor p27^Kip1 (p27) with unfavourable responses to chemotherapy and poor outcomes in NSCLC, supporting the hypothesis that the protein can execute oncogenic activities. In a recent issue of The Journal of Pathology, Calvayrac and coworkers uncover a novel molecular mechanism that can explain this oncogenic role of p27. They demonstrate that cytoplasmic p27 binds and inhibits the small GTPase RhoB and thereby relieves a selection pressure for RhoB loss that is frequently observed in NSCLC. This is supported not only by studies with genetically modified mice, but also through identification of a cohort of human lung cancer patients with cytoplasmic p27 and continued RhoB expression, where this signature correlates with decreased survival. This not only establishes a potentially useful biomarker, but also provides yet another facet of the complex roles p27 undertakes in tumourigenesis. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Cytoplasmic p27Kip1 promotes tumorigenesis via suppression of RhoB activity

The cell cycle inhibitor p27^Kip1 is a tumor suppressor via the inhibition of CDK complexes in the nucleus. However, p27 also plays other functions in the cell and may acquire oncogenic roles when located in the cytoplasm. Activation of oncogenic pathways such as Ras or PI3K/AKT causes the relocalization of p27 in the cytoplasm, where it can promote tumorigenesis by unclear mechanisms. Here, we investigated how cytoplasmic p27 participates in the development of non-small cell lung carcinomas. We provide molecular and genetic evidence that the oncogenic role of p27 is mediated, at least in part, by binding to and inhibiting the GTPase RhoB, which normally acts as a tumor suppressor in the lung. Genetically modified mice revealed that RhoB expression is preferentially lost in tumors in which p27 is absent and maintained in tumors expressing wild-type p27 or p27^CK- , a mutant that cannot inhibit CDKs. Moreover, although the absence of RhoB promoted tumorigenesis in p27^-/- animals, it had no effect in p27^CK- knock-in mice, suggesting that cytoplasmic p27 may act as an oncogene, at least in part, by inhibiting the activity of RhoB. Finally, in a cohort of lung cancer patients, we identified a subset of tumors harboring cytoplasmic p27 in which RhoB expression is maintained and these characteristics were strongly associated with decreased patient survival. Thus, monitoring p27 localization and RhoB levels in non-small cell lung carcinoma patients appears to be a powerful prognostic marker for these tumors. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

p27Kip1 promotes invadopodia turnover and invasion through the regulation of the PAK1/Cortactin pathway

p27^Kip1 (p27) is a cyclin-CDK inhibitor and negative regulator of cell proliferation. p27 also controls other cellular processes including migration and cytoplasmic p27 can act as an oncogene. Furthermore, cytoplasmic p27 promotes invasion and metastasis, in part by promoting epithelial to mesenchymal transition. Herein, we find that p27 promotes cell invasion by binding to and regulating the activity of Cortactin, a critical regulator of invadopodia formation. p27 localizes to invadopodia and limits their number and activity. p27 promotes the interaction of Cortactin with PAK1. In turn, PAK1 promotes invadopodia turnover by phosphorylating Cortactin, and expression of Cortactin mutants for PAK-targeted sites abolishes p27’s effect on invadopodia dynamics. Thus, in absence of p27, cells exhibit increased invadopodia stability due to impaired PAK1-Cortactin interaction, but their invasive capacity is reduced compared to wild-type cells. Overall, we find that p27 directly promotes cell invasion by facilitating invadopodia turnover via the Rac1/PAK1/Cortactin pathway.

DOI:http://dx.doi.org/10.7554/eLife.22207.001

When animals develop from embryos to adults, or try to heal wounds later in life, their cells have to move. Moving means that the cells must invade into their surroundings, a dense network of proteins called the extracellular matrix. The cell first attaches to the extracellular matrix; degrades it; and then moves into the newly opened space. Cells have developed specialized structures called invadosomes to enable all these steps. Invadosomes are never static, they first assemble where cells interact with extracellular matrix, they then release proteins that loosen the matrix, and finally disassemble again to allow cells to move. Invadosomes in cancer cells often become overactive, and can allow the tumor cells to spread throughout the body.

A lot of different proteins are involved in controlling how and when cells move. p27 is a well-known protein usually found in a cell’s nucleus along with the cell’s DNA. Inside the nucleus, p27 suppresses tumor growth by stopping cells from dividing. However, often in cancer cells p27 moves outside of the cell’s nucleus where it contributes to cell movement via an unknown mechanism.

To answer how p27 controls cell invasion, Jeannot et al. used a biochemical technique to uncover which proteins p27 binds to when it is outside of the nucleus. One of its interaction partners was called Cortactin. This protein is known to be an important building block of invadosomes, and is involved in both the assembly and disassembly of these structures. In further experiments, Jeannot studied mouse cells with or without p27 and human cancer cells that can be grown in the laboratory. The experiments revealed that p27 promotes an enzyme called PAK1 to also bind to Cortactin. PAK1 then modified Cortactin, causing whole invadosomes to disassemble, which in turn allowed cells to de-attach from the matrix and move forward. In contrast, cells lacking p27 had more stable invadosomes, attached more strongly to the matrix and were better at degrading it, but could not invade as well as cells with p27.

Overall these experiments showed a new way that p27 promotes cell invasion. The next steps will include finding out exactly how the modification of Cortactin causes the invadosomes to disassemble. Furthermore, it will be important to study whether forcing p27 back into the nucleus can reduce the spread of cancer cells in the body.

DOI:http://dx.doi.org/10.7554/eLife.22207.002

Functional characterization of AMP-activated protein kinase signaling in tumorigenesis

AMP-activated protein kinase (AMPK) is a ubiquitously expressed metabolic sensor among various species. Specifically, cellular AMPK is phosphorylated and activated under certain stressful conditions, such as energy deprivation, in turn to activate diversified downstream substrates to modulate the adaptive changes and maintain metabolic homeostasis. Recently, emerging evidences have implicated the potential roles of AMPK signaling in tumor initiation and progression. Nevertheless, a comprehensive description on such topic is still in scarcity, especially in combination of its biochemical features with mouse modeling results to elucidate the physiological role of AMPK signaling in tumorigenesis. Hence, we performed this thorough review by summarizing the tumorigenic role of each component along the AMPK signaling, comprising of both its upstream and downstream effectors. Moreover, their functional interplay with the AMPK heterotrimer and exclusive efficacies in carcinogenesis were chiefly explained among genetically altered mice models. Importantly, the pharmaceutical investigations of AMPK relevant medications have also been highlighted. In summary, in this review, we not only elucidate the potential functions of AMPK signaling pathway in governing tumorigenesis, but also potentiate the future targeted strategy aiming for better treatment of aberrant metabolism-associated diseases, including cancer.