Autophagy has recently been implicated in both the prevention and progression of cancer. However, the molecular basis for the relationship between autophagy induction and the initial acquisition of malignancy is currently unknown. Here, we provide the first evidence that autophagy is essential for oncogenic K-Ras (K-RasV12)-induced malignant cell transformation. Retroviral expression of K-RasV12 induced autophagic vacuole formation and malignant transformation in human breast epithelial cells. Interestingly, pharmacological inhibition of autophagy completely blocked K-RasV12-induced, anchorage-independent cell growth on soft agar. Both mRNA and protein levels of ATG5 and ATG7 (autophagy-specific genes 5 and 7, respectively) were increased in cells overexpressing K-RasV12. Targeted suppression of ATG5 or ATG7 expression by short hairpin (sh) RNA inhibited cell growth on soft agar and tumor formation in nude mice. Moreover, inhibition of reactive oxygen species (ROS) with antioxidants clearly attenuated K-RasV12-induced ATG5 and ATG7 induction, autophagy, and malignant cell transformation. MAPK pathway components were activated in cells overexpressing K-RasV12, and inhibition of JNK blunted induction of ATG5 and ATG7 and subsequent autophagy. In addition, pretreatment with antioxidants completely inhibited K-RasV12-induced JNK activation. Our results provide novel evidence that autophagy is critically involved in malignant transformation by oncogenic K-Ras and show that reactive oxygen species-mediated JNK activation plays a causal role in autophagy induction through up-regulation of ATG5 and ATG7.

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To prevent the development of malignancies, mammalian cells activate disposal programs, such as programmed cell death, in response to deregulated oncogene expression. However, the molecular basis for regulation of cellular disposal machinery in response to activated oncogenes is unclear at present. In this study, we show that upregulation of the autophagy-related protein, Atg5, is critically required for the oncogenic H-ras-induced autophagic cell death and that Rac1/mitogen-activated kinase kinase (MKK) 7/c-Jun N-terminal kinase (JNK) signals upregulation of Atg5. Overexpression of H-ras(V12) induced marked autophagic vacuole formation and cell death in normal fibroblasts, which remained unaffected by a caspase inhibitor. Pretreatment with Bafilomycin A1, an autophagy inhibitor, completely attenuated H-ras(V12)-induced cell death as well as autophagic vacuole formation. Selective production of Atg5 was observed in cells overexpressing H-ras(V12), and small interfering RNA (siRNA) targeting of Atg5 clearly inhibited autophagic cell death. Interestingly, inhibition of JNK or c-Jun by specific siRNA suppressed Atg5 upregulation and autophagic cell death. Moreover, inhibition of MKK7, but not MKK4, effectively attenuated H-ras(V12)-induced JNK activation. In addition, ectopic expression of RacN17 or Rac1-siRNA effectively inhibited MKK7-JNK activation, Atg5 upregulation and autophagic cell death. These data support the notion that upregulation of Atg5 is required for the oncogenic H-ras-induced autophagic cell death in normal fibroblasts and that activation of Rac1/MKK7/JNK-signaling pathway leads to upregulation of Atg5 in response to oncogenic H-ras. Our findings suggest that in cells acquiring deregulated oncogene expression, oncogenic stress triggers autophagic cell death, which protects cells against malignant progression.

Background: PTTG1 is an oncogene with its expression levels correlating with tumor development and metastasis. Results: Modulation of PTTG1 expression levels revealed that PTTG1 promotes invasive and migratory properties and expansion of CD44 high CD24 low cell population via AKT activation in breast cancer cells. Conclusion: PTTG1 induces EMT and promotes cancer stem cells via activation of AKT. Significance: PTTG1 represents a potential target for therapeutic intervention against the spread of breast cancer.

Claudins are identified as members of the tetraspanin family of proteins, which are integral to the structure and function of tight junction. Recent studies showed an increase in expression of claudins during tumorigenesis, which is associated with loss of cell-cell contact, dedifferentiation, and invasiveness. However, the molecular basis for the causal relationship between claudin expression and cancer progression is not fully understood yet. In this study, we show that claudin-1 plays a causal role in the acquisition of invasive capacity in human liver cells and that c-Abl-protein kinase C␦ (PKC␦) signaling is critical for Metastasis is the spread of cancer from its primary site to other places in the body, a process that is common in the late stages of cancer (1-4). It is a multistep process that involves migration of cancer cells from the primary tumor site, penetration into the vascular or lymphatic system, dispersal through the circulation, and extravasation and growth of malignant cells in the target organ (2, 3, 5). However, little is known about how malignant cells leave the primary site and begin to grow at distant sites; moreover, how the process of metastatic progression develops in cells is unknown. Thus, understanding the molecular basis for the spread of cancer, especially the development of invasive properties, is one of the most important issues in cancer research.Claudins (CLDs) 2 are a family of integral membrane proteins central to the formation of tight junctions, structures that are critical for the maintenance of cellular polarity, and are involved in paracellular transport and cellular growth and differentiation (6 -8). Recent studies have provided evidence that claudins are aberrantly expressed in diverse types of human cancers, including hepatocellular carcinomas (HCCs) (9 -11), and are associated with the development and progression of cancer. In this context, it has been shown that decreased or abnormal expression of claudin-4 (CLD4) or claudin-7 (CLD7) is correlated with liver metastases (12)(13)(14). Moreover, downregulation of claudin-2 (CLD2) has been implicated in the development and progression of breast carcinomas (4). Other reports, however, have suggested that increased CLD4 expression is associated with poor prognosis and high tumor grade in human breast cancer (15). In addition, overexpression of claudin-1 (CLD1) is associated with advanced stage disease in oral squamous cell carcinomas (16,17) and with angiolymphatic and perineural invasion, consistent with an aggressive tumor phenotype (16 -19). Moreover, CLD2, in combination with the epidermal growth factor receptor, has been shown to participate in tumor colonization in non-small cell lung cancer (20). These results indicate that the expression and functional significance of claudins may be highly specific for tumor cell type and depend on tumor grade.