ABSTRACT
Skeletal myogenesis is precisely regulated by multiple transcription factors. Previously, we demonstrated that enhancer of polycomb 1 (Epc1) induces skeletal muscle differentiation by potentiating serum response factor (SRF)-dependent muscle gene activation. Here, we report that an interacting partner of Epc1, ret finger protein (RFP), blocks skeletal muscle differentiation. Our findings show that RFP was highly expressed in skeletal muscles and was downregulated during myoblast differentiation. Forced expression of RFP delayed myoblast differentiation, whereas knockdown enhanced it. Epc1-induced enhancements of SRF-dependent multinucleation, transactivation of the skeletal α-actin promoter, binding of SRF to the serum response element, and muscle-specific gene induction were blocked by RFP. RFP interfered with the physical interaction between Epc1 and SRF. Muscles from rfp knockout mice (Rfp(-/-)) mice were bigger than those from wild-type mice, and the expression of SRF-dependent muscle-specific genes was upregulated. Myotube formation and myoblast differentiation were enhanced in Rfp(-/-) mice. Taken together, our findings highlight RFP as a novel regulator of muscle differentiation that acts by modulating the expression of SRF-dependent skeletal muscle-specific genes.
Subject(s)
DNA-Binding Proteins/metabolism , Muscle Cells/metabolism , Muscle Development/genetics , Nuclear Proteins/metabolism , Repressor Proteins/metabolism , Serum Response Factor/metabolism , Actins/genetics , Actins/metabolism , Animals , Binding Sites , Cell Differentiation , Cell Line , DNA-Binding Proteins/genetics , Gene Expression Regulation, Developmental , Mice , Mice, Knockout , Muscle Cells/cytology , Muscle Fibers, Skeletal/cytology , Muscle Fibers, Skeletal/metabolism , Myoblasts/cytology , Myoblasts/metabolism , Nuclear Proteins/genetics , Promoter Regions, Genetic , Repressor Proteins/genetics , Serum Response Factor/genetics , Transcription Factors , Transcriptional Activation , Ubiquitin-Protein LigasesABSTRACT
Germline mutations in the RET tyrosine kinase gene are responsible for the development of multiple endocrine neoplasia 2A and 2B (MEN2A and MEN2B). However, knowledge of the fundamental principles that determine the mutant RET-mediated signaling remains elusive. Here, we report increased expression of mitogen-activated protein kinase phosphatase-2 (MKP-2) in carcinomas developed in transgenic mice carrying RET with the MEN2A mutation (RET-MEN2A). The expression of MKP-2 was not only induced by RET-MEN2A or RET-MEN2B mutant proteins but also by the activation of endogenous RET by its ligand, glial cell line-derived neurotrophic factor (GDNF). MKP-2 expression was also evident in the MKK-f cell line, which was established from a mammary tumor developed in a RET-MEN2A transgenic mouse. Inhibition of MKP-2 attenuated the in vitro and in vivo proliferation of MKK-f cells, which was mediated by the suppression of cyclin B1 expression. Furthermore, we found that MKP-2 is highly expressed in medullary thyroid carcinomas derived from MEN2A patients. These findings suggest that the increased expression of MKP-2 may play a crucial role in oncogenic signaling downstream of mutant RET, leading to deregulation of cell cycle.
Subject(s)
Multiple Endocrine Neoplasia Type 2a/genetics , Neoplasms, Experimental/etiology , Protein Tyrosine Phosphatases/physiology , Proto-Oncogene Proteins c-ret/physiology , Animals , Cell Division , Cell Line, Tumor , Cell Proliferation , Cyclin B/antagonists & inhibitors , Cyclin B1 , Extracellular Signal-Regulated MAP Kinases/metabolism , Female , G2 Phase , Mice , Mice, Transgenic , Phosphorylation , Protein Tyrosine Phosphatases/geneticsABSTRACT
A 71-year-old woman was admitted to our hospital because of involuntary movement of the left upper extremity. MR image of the brain 15 days after the onset revealed the low intensity in right posterior limb of internal capsule. The lesion was surrounded by thalamus, subthalamic nucleus, and globus pallidus with enhancement by Gd-DTPA. Surface EMG revealed irregular grouped discharge in short duration and grouped discharge in long duration in the left upper extremity. Those features are compatible with one of choreoathetosis. Choreoathetosis due to cerebral infarction in acute phase is rare. We discussed pathophysiology of this involuntary movement due to lacunar infarction of posterior limb of internal capsule in acute phase.
