Characterization of 1700029J07RIK, a Novel Nuclear Membrane Associated Protein that is Induced During Skeletal Muscle Atrophy

Abstract

Skeletal muscle atrophy is the loss of muscle mass that results from myriad physiological conditions including denervation, corticosteroid exposure, and aging. 1700029J07RIK is a putative novel gene that is induced in skeletal muscle in response to denervation and is differentially regulated in Muscle RING Finger 1 (MuRF1) knockout mice compared to wild‐type mice. A previous microarray analysis of muscle tissue isolated from wild‐type control mice and MuRF1 knockout mice revealed that the expression of the 1700029J07RIK gene is unchanged at 3 days post‐denervation, while expression is significantly induced in wild‐type mice at 14 days post denervation but remains unchanged in the MuRF1‐null animals. It has been well established that muscle cells go through a distinct developmental timeline in which they proliferate as single cell myoblasts and then differentiate and fuse into multinucleated myotubes. Quantitative PCR was used to determine that the 1700029J07RIK gene is expressed in proliferating cells and increases in expression as muscle cells differentiate. In addition, the 1700029J07RIK cDNA was cloned from muscle cells and fused with green fluorescent protein and visualized by confocal fluorescent microscopy revealing an interesting cytoplasmic and nuclear membrane localization of the 1700029J07RIK protein in proliferating muscle cells that is not evident in differentiated muscle cells. Utilizing cellular fractionation, it was determined that 1700029J07RIK is localized to both the cytoplasmic and nuclear fractions in proliferating cells, but then appears to translocate into the nucleus as muscle cells differentiate. Interestingly, the 1700029J07RIK protein appears to undergo dramatic post‐translational modification as relocation to the nuclear compartment progresses. Finally, it was observed that overexpression of 1700029J07RIK resulted in inhibition of muscle cell differentiation and attenuation of the ERK1/2 branch of the MAP Kinase signaling pathway. While there is virtually nothing known about this novel gene in the context of skeletal muscle, the results presented here suggest 1700029J07RIK may play a role in muscle cell differentiation and in the skeletal muscle atrophy pathway.Support or Funding InformationThe work described in this study was supported by UNF Transformational Learning Opportunity grants, Academic Affairs Faculty Enhancement grants, a Dean’s Leadership Council Fellowship Award, a UNF Foundation Board Grant, and research start‐up funds from the University of North Florida.