Search

The p14(ARF) tumor suppressor functions as 'oncogenic checkpoint' that prevents unrestricted cellular proliferation in response to oncogenic signaling. Albeit, the major pathway through which ARF operates is the ARF-Mdm2-p53 axis, ARF directly binds to and inactivates transcription function of a number of DNA-bound activators. In the present study we show that p14(ARF) inhibits transcription activation of HIV-1 LTR promoter activity by Tat protein. Tat protein is a RNA-bound transcriptional activator whose function is strictly required for HIV-1 replication. We determined that p14(ARF) inhibits Tat transactivation of HIV-1 LTR by promoting Tat degradation via an ubiquitin-independent pathway.

In this study, we report that the human p14(ARF) associates in vivo with the N-Myc and inhibits N-Myc mediated transcriptional activation. We have determined that the region (aa 140-300) encompassing the N-Myc BoxIII is required for efficient interaction in vivo. Furthermore, we demonstrate that in the SK-N-BE neuroblastoma cell line p14(ARF) over-expression delocalized N-Myc from the nucleoplasm into nucleoli and that N-Myc regions required for interaction with p14(ARF) are also important for nucleoli co-localization. Finally, we determine that the N-terminal region of the p14(ARF) protein is involved in binding to c-Myc and N-Myc proteins.

Myc is a well known proto-oncogene encoding for a transcription factor whose activity is tightly regulated in the cellular context. Myc was the first oncogene recognized to activate the ARF tumor suppressor gene which suppresses cell proliferation partly through stabilization of the p53 tumor suppressor protein but which also has p53-independent growth-suppressive functions. Recent studies have indicated that mouse p19ARF negatively regulates Myc's transcriptional activity. We here show that the human p14ARF directly associates with Myc and relocates Myc from the nucleoplasm to the nucleolus. We found that p14ARF interacts with the Myc-Max complex and the binding of p14ARF does not interfere with Myc-Max interaction in vitro. Protein interaction assays define the Myc BoxII as a critical domain required for interaction with p14ARF. Moreover, we identify 30 amino acids encompassing Myc BoxII domain required for p14ARF interaction and colocalization in vivo. Finally, we show that p14ARF down regulates Myc activated transcription and that this activity cannot be addressed to an intrinsic p14ARF repressor domain.