KAP1 (TRIM28) is a transcriptional regulator in embryonic development that controls stem cell self-renewal, chromatin organization, and the DNA damage response, acting as an essential corepressor for KRAB family zinc finger proteins (KRAB-ZNF). To gain insight into the function of this large gene family, we developed an antibody that recognizes the conserved zinc fingers linker region (ZnFL) in multiple KRAB-ZNF. Here, we report that the expression of many KRAB-ZNF along with active SUMOlyated KAP1 is elevated widely in human breast cancers. KAP1 silencing in breast cancer cells reduced proliferation and inhibited the growth and metastasis of tumor xenografts. Conversely, KAP1 overexpression stimulated cell proliferation and tumor growth. In cells where KAP1 was silenced, we identified multiple downregulated genes linked to tumor progression and metastasis, including EREG/epiregulin, PTGS2/COX2, MMP1, MMP2, and CD44, along with downregulation of multiple KRAB-ZNF proteins. KAP1-dependent stabilization of KRAB-ZNF required direct interactions with KAP1. Together, our results show that KAP1-mediated stimulation of multiple KRAB-ZNF contributes to the growth and metastasis of breast cancer. Cancer Res; 75(2); 1–12. ©2014 AACR.

KAP1 (TRIM28) is a transcriptional regulator in embryonic development that controls stem cell self-renewal, chromatin organization and the DNA damage response, acting as an essential co-repressor for KRAB family zinc finger proteins (KRAB-ZNF). To gain insight into the function of this large gene family, we developed an antibody that recognizes the conserved zinc fingers linker region (ZnFL) in multiple KRAB-ZNF. Here we report that the expression of many KRAB-ZNF along with active SUMOlyated KAP1 is elevated widely in human breast cancers. KAP1 silencing in breast cancer cells reduced proliferation and inhibited the growth and metastasis of tumor xenografts. Conversely, KAP1 overexpression stimulated cell proliferation and tumor growth. In cells where KAP1 was silenced, we identified multiple downregulated genes linked to tumor progression and metastasis, including EREG/epiregulin, PTGS2/COX2, MMP1, MMP2 and CD44, along with downregulation of multiple KRAB-ZNF proteins. KAP1-dependent stabilization of KRAB-ZNF required direct interactions with KAP1. Together, our results show that KAP1-mediated stimulation of multiple KRAB-ZNF contributes to the growth and metastasis of breast cancer.

Vascular tumors are endothelial cell neoplasms whose mechanisms of tumorigenesis are poorly understood. Moreover, current therapies, particularly those for malignant lesions, have little beneficial effect on clinical outcomes. In this study, we show that show that endothelial activation of the Akt1 kinase is sufficient to drive de novo tumor formation. Mechanistic investigations uncovered opposing functions for different Akt isoforms in this regulation, where Akt1 promotes and Akt3 inhibits vascular tumor growth. Akt3 exerted negative effects on tumor endothelial cell growth and migration by inhibiting activation of the translation regulatory kinase S6K through modulation of Rictor expression. S6K in turn acted through a negative feedback loop to restrain Akt3 expression. Conversely, S6K signaling was increased in vascular tumor cells where Akt3 was silenced, and the growth of these tumor cells was inhibied by a novel S6K inhibitor. Overall, our findings offer a preclinical proof of concept for the therapeutic utility of treating vascular tumors such as angiosarcomas with S6K inhibitors.

βIII-tubulin (encoded by TUBB3) expression is associated with therapeutic resistance and aggressive disease in non–small cell lung cancer (NSCLC), but the basis for its pathogenic influence is not understood. Functional and differential proteomics revealed that βIII-tubulin regulates expression of proteins associated with malignant growth and metastases. In particular, the adhesion-associated tumor suppressor maspin was differentially regulated by βIII-tubulin. Functionally, βIII-tubulin suppression altered cell morphology, reduced tumor spheroid outgrowth, and increased sensitivity to anoikis. Mechanistically, the PTEN/AKT signaling axis was defined as a critical pathway regulated by βIII-tubulin in NSCLC cells. βIII-Tubulin blockage in vivo reduced tumor incidence and growth. Overall, our findings revealed how βIII-tubulin influences tumor growth in NSCLC, defining new biologic functions and mechanism of action of βIII-tubulin in tumorigenesis. Cancer Res; 75(2); 1–11. ©2014 AACR.

Beta human papillomaviruses (HPV) have been suspected to be carcinogenic in nonmelanoma skin cancers (NMSC), but the basis for potential viral contributions to these cancers is poorly understood. In particular, it is unresolved how HPV-infected keratinocytes escape cell-cycle control and whether their cross-talk with immune cells is critical for tumorigenesis. In nonviral preclinical models, the angiogenic cytokine VEGF-A has been identified as a critical regulator of NMSC. In this study, we dissected the contribution of epidermal versus myeloid cell–derived VEGF-A in HPV-mediated skin cancer by interbreeding an HPV8 transgenic mouse model with a conditional disruption of VEGF-A restricted to either epidermal or myeloid cells. Although only epidermal-derived VEGF-A was essential for initiation of skin tumor development, both spontaneously and UV-light triggered, both epidermal and myeloid cell–derived VEGF-A contributed to regeneration-induced tumorigenesis upon HPV8 overexpression, partly not only through a paracrine effect on endothelial cells, but also most probably through an additional autocrine effect on epidermal cells. Our findings offer new mechanistic insights into distinct functions of epidermal versus myeloid cell–derived VEGF-A during HPV-mediated tumorigenesis, with possible implications for preventing this disease. Cancer Res; 75(2); 1–14. ©2014 AACR.