POST-TRANSLATIONAL REGULATION OF INDUCIBLE CAMP EARLY REPRESSOR AND ITS IMPLICATIONS IN CANCER

Project Summary/Abstract Even though Inducible cAMP Early Repressor (ICER) has the functional characteristics of a tumorsuppressor, there is no genetic evidence to demonstrate that ICER is a bona fide tumor suppressor geneproduct. Thus, altered post-translational events might be the cause of the observed abnormalities of ICERprotein expression in cancer cells. On this basis it is hypothesized that in cancer cells, ICER isderegulated by ubiquitination resulting in constitutive proteasomal degradation and/or abnormalsubcellular localization. Finding alternatives to rescue endogenous ICER nuclear expression in malignantcells could lead to the development of novel cancer treatment modalities. Through this project, we will studythe mechanisms and physiological consequences of ICER ubiquitination and subcellular localization. We willuse melanoma as a paradigm for the study. This study will focus on two specific aims.Aim 1. Determine the functional and physiological consequences of ICER ubiquitination bycharacterizing the specific ubiquitination sites on ICER and ubiquitin E3 ligases using biochemistry,chromatin binding, and siRNA techniques.Aim 2. Examine the effect on tumorgenesis upon expression of ubiquitinatable -deficient ICER usingmouse xenograft models and an established zebrafish model for melanoma. The overarching goal of this project is to determine the functional consequences of ICER post-translational modifications in cancer. The experiments described in this proposal will provide the basis for moreextensive analyses of multi-component complexes associated with the regulation of ICER in cancer cells.Subsequent research will: 1) Use the zebrafish melanoma model to further characterize the molecularmechanisms of ICER ubiquitination during melanoma genesis; 2) Establish collaborative efforts to developsmall-molecule compounds and small ICER-related peptides as specifics Ub-ligases inhibitors to test specificapproaches to restore endogenous ICER nuclear expression in cancer cells; and 3) Study the effect of theseUb-ligase inhibitors in animal models for cancer.>