PgmNr W4034: Analysis of DLC-1 mediated regulation of the tumor suppressor protein GLD-1.

Authors:
M. Ellenbecker; E. Voronina


Institutes
University of Montana, Missoula, MT.


Keyword: Other ( RNA regulation )

Abstract:

Dynein light chain (DLC-1) was originally characterized as a cargo-binding component of the dynein motor complex that is involved in retrograde transport of mRNA and protein particles.  More recent studies have revealed that DLC-1 interacts with a diversity of cellular proteins and likely also functions as an allosteric regulator in ribonucleoprotein complexes (mRNPs).  Data from the Voronina lab suggests that DLC-1 regulates developmentally important mRNA expression by functioning as a cofactor to RNA binding proteins such as FBF-2 and GLD-1.  GLD-1 is an RNA-binding protein that promotes germ cell differentiation during animal development by binding to and repressing translation of target mRNAs.  This RNA regulatory function is essential for preventing ectopic proliferation in germ cells and gld-1 mutant worms form germline tumors.  Mammalian Quaking proteins are GLD-1 orthologs and function as potent glioblastoma multiforme tumor suppressors regulating the TGFβ signaling network that controls cell growth, proliferation and differentiation.  RNA immunoprecipitation and microarrays or transcriptome wide sequencing experiments have identified hundreds of mRNAs as potential GLD-1 targets, however, the mechanism(s) of GLD-1 regulation of this diverse set of mRNAs is not well understood.  We discovered that mutation in dlc-1 gene predisposes nematode to tumor formation, GLD-1 target mRNAs are enriched in DLC-1 ribonucleoprotein complexes and that DLC-1 regulates translation of the GLD-1 target mRNA mex-3.  Depletion of dlc-1 using RNA interference disrupts the GLD-1-dependent control of germ cell proliferation and differentiation and biochemical assays show a direct DLC-1/GLD-1 binding interaction.  Together, these data support the hypothesis that DLC-1 mediates the RNA regulatory and tumor suppressor functions of GLD-1 through a direct protein interaction.  Some mechanistic possibilities for DLC-1 promoting the function(s) of GLD-1 are: regulating GLD-1 levels in germ cells, enhancing formation of GLD-1 mRNP complexes, cooperating in translational repression of GLD-1 mRNA targets and/or by mediating GLD-1 sub-cellular localization.  We are currently using genetic and molecular biology techniques to determine how DLC-1 contributes to GLD-1 function in vivo and biochemical studies to elucidate the molecular details of the DLC-1/GLD-1 binding interaction.  Since GLD-1 and mammalian Quaking proteins are closely related and their mutation causes cancer, molecular insights into germline tumor formation identified in this study using C. elegans as a model organism will be broadly relevant and significantly advance our understanding of human cancers.