Sub-Nuclear Localization and Tumorigenic Function of the Oncoprotein Dek.

Abstract

The human DEK gene is overexpressed in a number of malignancies, however its potential function in the context of cancer remains unknown. DEK has been implicated in a diverse set of cellular processes, including regulation of transcription, chromatin architecture, mRNA processing, and cell signaling. Regulation of the participation of DEK in these disparate functions is thought to be achieved through differential post-translational modification. We demonstrate that a fraction of nuclear DEK is acetylated in vivo. Acetylation of DEK results in the accumulation of DEK in interchromatin granule clusters, dense sub-nuclear structures enriched in mRNA processing factors. Overexpression of the acetylase p300/CBP-associated factor was sufficient to cause migration of DEK into interchromatin granule clusters. Inhibition of transcription similarly altered the sub-nuclear distribution of DEK, causing accumulation of DEK in both interchromatin granule clusters, as well as other sub-nuclear structures. The significance of DEK overexpression in melanoma was also addressed. Metastatic melanoma lines displayed remarkably increased expression of DEK as compared to normal melanocytes. Inhibition of DEK expression by shRNA interference revealed two oncogenic contributions of DEK. Knockdown of DEK expression resulted in the induction of the cyclin-dependent kinase inhibitor p21CIP1. In some, but not all melanomas, the expression of p21CIP1 was accompanied by the induction of cellular senescence. These findings suggest that overexpression of DEK may represent an event in melanoma development required to evade tumor suppression through cell cycle arrest and senescence. In addition to its anti-senescence function, DEK overexpression in melanoma also conferred remarkable chemoresistance to both the DNA damaging agent doxorubicin and the BH3 mimetic compound TW-37. This effect was independent of p53, as inhibition of DEK expression did not alter p53 accumulation or activity in response to doxorubicin. Instead, knockdown of DEK expression sensitized melanoma through downregulation of a member of the anti-apoptotic Bcl-2 family, Mcl-1. Knockdown of DEK expression resulted in reduced activity of the mcl-1 promoter and consequently reduced mcl-1 mRNA. These results demonstrate a novel transcriptional mechanism of Mcl-1 overexpression in melanoma that confers remarkable chemoresistance. This work establishes DEK as a melanoma oncoprotein with both anti-senescence and anti-apoptotic functions.Ph.D.ImmunologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75982/1/mkhodado_1.pd