Abstract 2264: HIC (MDFIC) is a protein that interacts and colocalizes with the RELT family of TNFRs
Authors: Cusick John K. , Sumida Cara , Checketts Matthew , Reyland Mary E. , Jacobs Aaron T. 
Published: May 2015

Tumor necrosis factor receptors (TNFRs) have been recognized to be critically important for cellular processes such as apoptosis, cell proliferation and inflammatory responses. Aberrations in TNFR signaling have been implicated in a wide range of human diseases such as cancer, autoimmune diseases and developmental abnormalities. Receptor Expressed in Lymphoid Tissues (RELT) is a recently identified human TNFR that has two identified homologous binding partners RELL1 and RELL2. This study sought to further elucidate the function of RELT by identifying novel protein interactions with RELT family members. Human I-mfa domain-containing protein (HIC), also known as MDFIC, was identified in a genetic screen for novel RELL1 binding partners. HIC is a transcription factor that was initially identified to differentially regulate HTLV and HIV gene expression. HIC is now known to regulate many other cellular processes and the hic gene is located proximally to regions of chromosome 7 (7q31.1) frequently lost in Acute Myeloid Leukemia (AML) patients. Our current studies indicate that HIC physically interacts with both RELT and RELL1, as determined by in vitro co-immunoprecipitations. Immunohistochemistry was utilized to determine whether HIC co-localizes with RELT family members using Human Embryonic Kidney (HEK-293) cells. HIC was observed to co-localize with RELL1 at the plasma membrane of HEK-293 cells and appeared to co-localize with RELT in intracellular compartments. A series of deletion mutants of RELT were created that could be used to identify the regions of RELT required to bind to HIC. Site-directed mutagenesis was utilized to create eight (8) deletion mutants of RELT that lacked differing portions of the intracellular domain. Interestingly, mutants that were designed to lack more than 60 intracellular amino acids proximal to the plasma membrane were barely detectable by overexposing Western blots, and this may indicate that the regions of RELT immediately proximal to the plasma membrane are required for protein stability. Current ongoing studies involve using the created deletion mutants of RELT to identify which regions of RELT are required to bind HIC, and to identify the physiological significance of these protein interactions. It is interesting to note that the hematologically expressed RELT was previously identified to interact with PLSCR1, a protein that induces cell cycle arrest, differentiation and apoptosis of AML cells. Therefore the discovery that RELT also binds to HIC, a protein that is highly expressed in leukocytes and is located in a region of chromosome 7 frequently lost in AML patients, is intriguing and warrants further study.

Citation Format: John K. Cusick, Cara Sumida, Matthew Checketts, Mary E. Reyland, Aaron T. Jacobs. HIC (MDFIC) is a protein that interacts and colocalizes with the RELT family of TNFRs. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2264. doi:10.1158/1538-7445.AM2014-2264