Post-Transcriptional Regulation of KLF4 by High-Risk Human Papillomaviruses Is Necessary for the Differentiation-Dependent Viral Life Cycle.

Human papillomaviruses (HPVs) are epithelial tropic viruses that link their productive life cycles to the differentiation of infected host keratinocytes. A subset of the over 200 HPV types, referred to as high-risk, are the causative agents of most anogenital malignancies. HPVs infect cells in the basal layer, but restrict viral genome amplification, late gene expression, and capsid assembly to highly differentiated cells that are active in the cell cycle. In this study, we demonstrate that HPV proteins regulate the expression and activities of a critical cellular transcription factor, KLF4, through post-transcriptional and post-translational mechanisms. Our studies show that KLF4 regulates differentiation as well as cell cycle progression, and binds to sequences in the upstream regulatory region (URR) to regulate viral transcription in cooperation with Blimp1. KLF4 levels are increased in HPV-positive cells through a post-transcriptional mechanism involving E7-mediated suppression of cellular miR-145, as well as at the post-translational level by E6-directed inhibition of its sumoylation and phosphorylation. The alterations in KLF4 levels and functions results in activation and suppression of a subset of KLF4 target genes, including TCHHL1, VIM, ACTN1, and POT1, that is distinct from that seen in normal keratinocytes. Knockdown of KLF4 with shRNAs in cells that maintain HPV episomes blocked genome amplification and abolished late gene expression upon differentiation. While KLF4 is indispensable for the proliferation and differentiation of normal keratinocytes, it is necessary only for differentiation-associated functions of HPV-positive keratinocytes. Increases in KLF4 levels alone do not appear to be sufficient to explain the effects on proliferation and differentiation of HPV-positive cells indicating that additional modifications are important. KLF4 has also been shown to be a critical regulator of lytic Epstein Barr virus (EBV) replication underscoring the importance of this cellular transcription factor in the life cycles of multiple human cancer viruses.

RanGTPase: a candidate for Myc-mediated cancer progression.

BACKGROUND: Ras-related nuclear protein (Ran) is required for cancer cell survival in vitro and human cancer progression, but the molecular mechanisms are largely unknown. METHODS: We investigated the effect of the v-myc myelocytomatosis viral oncogene homolog (Myc) on Ran expression by Western blot, chromatin immunoprecipitation, and luciferase reporter assays and the effects of Myc and Ran expression in cancer cells by soft-agar, cell adhesion, and invasion assays. The correlation between Myc and Ran and the association with patient survival were investigated in 14 independent patient cohorts (n = 2430) and analyzed with Spearman's rank correlation and Kaplan-Meier plots coupled with Wilcoxon-Gehan tests, respectively. All statistical tests were two-sided. RESULTS: Myc binds to the upstream sequence of Ran and transactivates Ran promoter activity. Overexpression of Myc upregulates Ran expression, whereas knockdown of Myc downregulates Ran expression. Myc or Ran overexpression in breast cancer cells is associated with cancer progression and metastasis. Knockdown of Ran reverses the effect induced by Myc overexpression in breast cancer cells. In clinical data, a positive association between Myc and Ran expression was revealed in 288 breast cancer and 102 lung cancer specimens. Moreover, Ran expression levels differentiate better or poorer survival in Myc overexpressing breast (χ2 = 24.1; relative risk [RR] = 9.1, 95% confidence interval [CI] = 3.3 to 24.7, P < .001) and lung (χ2 = 6.04; RR = 2.8, 95% CI = 1.2 to 6.3; P = .01) cancer cohorts. CONCLUSIONS: Our results suggest that Ran is required for and is a potential therapeutic target of Myc-driven cancer progression in both breast and lung cancers.

Osteopontin as a target for cancer therapy.

Osteopontin (OPN) is a glycophosphoprotein cytokine that has multiple functions. OPN is expressed and secreted by various cells, and has a role in cell adhesion, chemotaxis, prevention of apoptosis, invasion, migration and anchorage-independent growth of tumor cells. Extensive research has demonstrated the pivotal participation of OPN in the regulation of cell signaling which controls neoplastic and malignant transformation. The elevated expression of OPN has been observed in a variety of cancers. OPN has been linked with tumor metastasis and signifies a poor prognosis for the patient. This review details the mechanisms by which OPN facilitates these pathological events. It will also show that gaining an understanding of the mechanism of OPN's action at a cellular level has led to the development of a number of therapeutic strategies against the cytokine. These include inhibiting its expression, antagonizing cell surface receptor activation and blocking downstream cell signaling pathways. In addition to the potential of these therapies, serum levels of OPN could be used as a diagnostic and prognostic marker. The authors propose that with further research and development, osteopontin directed treatment could greatly enhance outcomes for cancer patients.